WO2009158046A1 - Polymer composite formulations from poly(vinylidine fluoride) (pvdf) and cyanoacrylates (ca) and methods for use in large-area applications - Google Patents

Abstract

A polymeric composition including a blend of poly(vinylidine fluoride) and at least one cyanoacrylate (CA), which provides a polymeric composite that exhibits useful characteristics of both materials. Rosin and/or boiled linseed oil may be included in the composition, such as to inhibit polymerization of the cyanoacrylate. Alternatively, the cyanoacrylate may be provided by a solution containing a CA polymer (for example ethyl 2-cyanoacrylate polymer). Several different co-solvents can be used to control the polymerization of CA. In addition, fillers such as micro/nanoparticles or their combinations may be included to allow tuning of the hydrophobicity of the composite and/or other characteristics. Further, the polymeric composition, including a blend of PVDF and at least one CA, may be coated onto a substrate and cured to form a film adhered to the substrate.

Description

POLYMER COMPOSITE FORMULATIONS FROM

POLY(VINYLIDINE FLUORIDE) (PVDF) AND CYANO ACRYLATES (CA) AND METHODS FOR USE IN LARGE- AREA APPLICATIONS

CROSS REFERENCE TO RELATED APPLICATIONS

[01] This international application claims the benefit of U.S. provisional application Serial No. 61/076,328 filed June 27, 2008, and of U.S. provisional application Serial No. 61/096,412 filed September 12, 2008, which are incorporated herein by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

[02] This invention is related to the area of polymer composites including poly(vinylidine fluoride) (PVDF). In particular, it relates to PVDF polymer composites comprising PVDF and cyanoacrylates (CA), plus optionally fillers.

BACKGROUND OF THE INVENTION

[03] Poly(vinylidine fluoride) (PVDF) is a polymer with exceptional chemical resistance, thermal stability and outstanding dielectric and piezoelectric properties, which justify its widespread use in many industries, for example as ultrafiltration and microfϊltration membrane materials, in lithium ion batteries, and in developing organic/inorganic or all- organic electro-mechanical composite materials. PVDF is characterized by having a repeating monomer of the following structure: -[CH₂-CF₂]-

[04] In addition, because it is a biocompatible polymer, PVDF has been used to prepare, for instance, special bioactive surfaces facilitating cellular proliferation and adhesion in human osteogenesis, in soft tissue applications, and as a suture material. However, in applications where surface adhesion is critical, use of PVDF poses a severe challenge due to its inherent hydrophobicity and chemical inertness against functionalization. Furthermore, due to its chemical inertness and poor adhesion characteristics, dispersion of functional fillers, such as nanoparticles, in PVDF is poor. [05] Although polymer blending in solution is an easy and cost-effective technique, insolubility of PVDF in many common solvents hinders its potential use in polymer composites. In order to facilitate practical applications in the coatings industry, the search for other secondary polymer components for enhancing adhesion, pigment dispersion, and morphological and piezoelectric properties of PVDF is ongoing. Blends of PVDF with suitable acrylic resins have been developed, which improve PVDF 's pigment wetting and coating adhesion. For example, polymethylmethacrylate) (PMMA) is miscible with PVDF in solution at any proportion. A two-component (PVDF+PMMA) polymer composite system has been developed and commercialized for outdoor applications. This composite system provides a combination of the excellent resistance of PVDF to extreme environmental conditions, such as ultraviolet light and humidity, and the enhanced adhesion of PMMA. However, PMMA is not an electro-mechanically active polymer. Thus, in applications where electro-mechanical properties of PVDF are critical, the presence of PMMA can be disadvantageous. Further, PMMA is not biocompatible, a notable disadvantage for biological applications.

[06] An alternative for enhancing adhesion of PVDF blends that has been explored is the use of a highly functional and biocompatible class of acrylics, known as cyanoacrylates (CA; i.e., super glue). The cyano (C≡N) group present in a cyanoacrylate monomer is electro-active, having ferroelectric functionality, which makes CAs highly suitable for many applications, such as bone fillers enabling enhanced osteobonding and new bone growth due to polarization of the cyano group. Furthermore, cyanoacrylates display superior adhesion strength compared to other acrylics and they cure rapidly in biomedically favorable moist environments. As a result, CAs are becoming increasingly important materials as tissue adhesives and sealants for various surgical procedures.

[07] One challenge to forming two-component systems of PVDF and CA is the need for a compatible solvent. Dimethyl formamide (DMF) is the most common solvent for PVDF, however, DMF acts as a catalyst for rapid polymerization of CA monomer in solution, thus making DMF unsuitable for blending CA with PVDF. Accordingly, there is a need in the art to develop a formulation that will allow successful blending of PVDF and CA in solution to obtain a polymer composite that exhibits the advantageous characteristics of both materials.

SUMMARY OF THE INVENTION

[08] An embodiment of the invention is a polymeric composition comprising a blend of poly(vinylidine fluoride) and at least one cyanoacrylate (CA). Rosin may be included in the composition to inhibit polymerization of the cyanoacrylate.

[09] Another aspect of the invention is a polymeric composition comprising a blend of poly(vinylidine fluoride) and at least one starting cyanoacrylate monomer. For example, the CA monomer may be an ethyl 2-cyanoacrylate. The monomer can be polymerized in a controlled fashion in solution in the presence of DMF.

[10] A further aspect of the invention is a use of a polymeric composition comprising a blend of poly(vinylidine fluoride) and at least one cyanoacrylate (CA), comprising coating the composition onto a substrate and curing the composition to form a film on the substrate. The substrate may be a rigid or flexible material (metal, plastic, etc.).

[11] Another aspect of the invention is the incorporation of functional filler micro/nanoparticles. Both surface functionalized and non-functionalized fillers can be added to the blends of poly(vinylidine fluoride) and at least one cyanoacrylate (CA) to provide coatings with controllable surface energy (wettability), morphology and other useful properties, such as chemical inertness, enhanced environmental stability, thermal stability, improved electrical characteristics and many others.

[12] These and other embodiments will be apparent to those of skill in the art upon reading the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[13] Fig. l(a) illustrates aluminum foil coated with a CA/rosin dispersion containing zinc oxide particles but no PVDF. [14] Fig. l(b) illustrates aluminum foil coated with a PVD F/C A/rosin dispersion containing zinc oxide particles.

[15] Fig. l(c) is a graph that illustrates the change in elastic modulus and peel strength of nanocomposite coating over a range of PVDF/CA blend weight ratios and with varying amounts of zinc oxide.

[16] Fig. 2(a) is a scanning electron microscope (SEM) micrograph of an uncoated glass fiber.

[17] Fig. 2(b) is a SEM micrograph of a glass fiber covered with ZnO nanopowder-filled PVDF/CA/rosin coating.

[18] Fig. 2(c) is a SEM micrograph of a bundle of glass fibers with a microporous PVDF/CA/rosin coating.

[19] Fig. 3(a) is a graph of water contact angle variation as a function of applied tensile stress on woven fiberglass cloths coated with PVDF/CA/rosin/ZnO, containing unmodified ZnO nanopowder.

[20] Fig. 3(b) is a graph of water contact angle variation as a function of applied tensile stress on woven fiberglass cloths coated with PVDF/CA/rosin/ZnO, containing functionalized ZnO.

[21] Fig. 4(a) is a SEM micrograph of an edge portion of a drop-cast PVDF/polyCA film.

[22] Fig. 4(b) is a SEM micrograph of a portion very near the edge of a drop-cast PVDF/polyCA film.

[23] Fig. 4(c) is a SEM micrograph of a middle portion of a drop-cast PVDF/polyCA film.

[24] Fig. 4(d) is a SEM micrograph of the center portion of a drop cast PVDF/polyCA film. [25] Fig. 5 shows a schematic of a drop cast PVDF/polyCA film to illustrate the locations of the film portions shown in the micrographs of Fig 4(a) - Fig. 4(d).

[26] Fig. 6 is an x-ray diffraction plot of PVDF/polyCA films.

[27] Fig. 7(a) is a graph of water droplet contact line diameter versus time for PVDF/polyCA films in the droplet spreading stages.

[28] Fig. 7(b) is a graph of water droplet contact line diameter versus time for PVDF/polyCA films in the droplet receding stages.

[29] Fig. 8(a) is a graph of water droplet contact line diameter versus time for PVDF/polyCA films in the droplet spreading stages.

[30] Fig. 8(b) is a graph of water droplet contact line diameter versus time for PVDF/polyCA films in the droplet receding stages.

[31] Fig. 9 is a graph of the dynamic contact angle of water droplets impacting rigid PVDF/polyCA films.

[32] Fig. 10 is a graph of estimated surface energy of PVDF/polyCA films.

[33] Figs. 11 (a) - l l(d) are SEM micrographs of a ZnO nanoparticle-laden PVDF/polyCA film, at different magnifications.

[34] Figs. 12(a) - 12(d) are SEM micrographs of a ZnO nanoparticle-laden PVDF/polyCA film modified with rosin and layered silicate particles, at different magnifications.

[35] Fig. 13 illustrates a water droplet impact and bounce back on a ZnO-in-PVDF/polyCA nanocomposite surface.

[36] Fig. 14 is a graph of the change in water and water + IPA mixture contact angle with content of ZnO nanoparticles in the coating [37] Fig. 15 is a graph of the change in water and water + IPA mixture contact angle with content of PTFE microparticles in the coating.

[38] Fig. 16 is a graph of the change in water and water + IPA mixture contact angle with content of ZnO microparticles in the coating.

[39] Fig. 17 is a graph of the change in water and water + IPA mixture contact angle with content of PTFE microparticles and ZnO nanoparticles in the coating.

[40] Fig. 18 is a graph of the change in water and water + IPA mixture contact angle with content of ZnO microparticles and ZnO nanoparticles in the coating.

DETAILED DESCRIPTION OF THE INVENTION

[41] As noted above, a potential secondary polymer component that may be employed for enhancing adhesion of PVDF blends is a highly functional and biocompatible class of acrylics, known as cyanoacrylates. For example, the alkyl esters of 2-cyanoacrylic acid (cyanoacrylates, CAs) have been used as instant curing adhesives for various substrates, ranging from metals and plastics, to living tissue. An important alternative is 2-Octyl cyanoacrylate (FDA approved) known as Dermabond, a commonly used wound adhesive. Other higher molecular weight CAs can also be used. These CAs can be obtained by altering the alkoxycarbonyl (-COOR) group of the molecule to obtain CA compounds of different chain lengths. A strong adhesive bond is achieved at room temperature, without use of catalysts or pressure, within a short time period, ranging from several seconds to several minutes. The adhesive action is the result of exothermal anionic polymerization, initiated by adsorbed moisture on the surface. However, many polar and environmentally friendly solvents react with CAs through nucleophilic polymerization. As such, the instant polymerization of CAs hinders their applications in solution-based polymer composites.

[42] Another drawback of CAs is their inability to disperse nanoparticles that are comprised mostly of metal or metal oxide, due to the existence of naturally adsorbed moisture on the surface of these particles. CA pastes containing a number of inorganic fillers were developed particularly for dental applications, and some instant polymerization inhibitors, such as weak acids, have been suggested to enable particle dispersion in such CA compositions. Finally, use of surfactants in CA systems is again nearly impossible due to instant reaction of CAs with various ionic and anionic surfactants in solution.

[43] Combining the superior adhesion properties of CAs with PVDF can open new avenues in PVDF-based polymer composite applications. It has been discovered that polymer composites comprising PVDF and CAs may successfully be prepared and provide the beneficial characteristics of both materials. Aspects of the present invention demonstrate simple solution-based techniques to provide PVDF-CA polymer composites wherein the CA component imparts improved characteristics, such as substrate adhesion, rapid curing at low temperatures and improved pigment dispersion.

[44] Dimethylformamide (DMF) is the solvent almost universally used in processing PVDF. DMF and CA react violently to polymerize CA, though, thus making it impossible to disperse CA in DMF directly. However, several techniques are provided by the present invention to overcome this difficulty. In one aspect, the CA monomer, for instance ethylcyanoacrylate, is polymerized in a controlled manner. Through such slow polymerization, a polymer having a high degree of polymerization (polyCA) is obtained, resulting in lower residual strain and elevated flexibility, in comparison with CA polymers obtained by rapid polymerization. For example, the ethylcyanoacrylate monomer may be partially polymerized in DMF in the presence of an appropriate co- solvent prior to mixing, for instance methyl ethyl ketone (MEK) or acetone, thus blends of PVDF and polymerized CA are made possible, and are referred to herein as "PVDF- polyCA" or "PVDF/polyCA." Suitable co-solvents are ketones and acetates. These are generally used to disperse cyanoacrylates. Ideal PVDF to polyCA weight ratios would be 60:40 or 70:30, much like commercial PVDF/PMMA coating formulations.

[45] In a further aspect of the invention, an alternative co-solvent based technique to control the polymerization reaction of cyanoacrylates (CA) is provided. This technique eliminates the need for cooling, which is typically used to remove the heat generated by exothermic polymerization of CA in the presence of DMF. In such embodiments, boiled linseed oil (BLO), a common drying oil frequently used in woodworking as a water and oil resistant coating, is incorporated in the solvent blend. It is known that the presence of weak carboxylic acids in solution hinders rapid exothermic polymerization of CAs in solution. Linseed oil is a natural fatty acid, with typical fatty acid content by weight as follows: Palmitic acid 6.0; Stearic acid 2.5; Arachidic acid 0.5; Oleic acid 19; Linoleic acid 24.1; Linolenic acid 47.4. For example, a CA monomer solution in either methyl ethyl ketone (MEK) or acetone may be prepared, then drops of BLO are added to the solution and stirred. The solution will become visibly thicker, indicating that the CA is polymerizing. This polyCA solution may then be blended with a solution of PVDF in DMF to form a PVDF-polyCA composite.

[46] In alternate embodiments of the invention, PVDF/CA solution blends may be prepared in the presence of rosin. As noted above, it is known that presence of weak acids in solution can help control or even hinder CA polymerization; however, incorporation of acids in multi-component polymer solutions can cause dispersion instability and unwanted reactions. It was discovered that rosin, a natural resin, which is commercially used in printing ink, varnish, adhesive and soldering flux formulations, inhibits CA polymerization in solution even in the presence of DMF, and is miscible with CA at any proportion in solution. This polymerization inhibition could be due to the fact that abietic acid, which naturally occurs in rosin, is a weak carboxylic acid. To demonstrate the ability of rosin to inhibit the polymerization of CA in DMF, a methyl ethyl ketone (MEK) dispersed CA monomer (2-ethylcyanoacrylate, Sigma-Aldrich, USA) was directly blended with rosin (Sigma-Aldrich, USA) stock solution consisting of a 60 wt. % rosin dispersion in isopropyl alcohol/castor oil (7/1 in wt.) solvent. When the PVDF in DMF solution was added to the mixture, no spontaneous polymerization of CA monomer was observed. Weak acids have been proposed in the past in order to inhibit CA polymerization, however, no prior work has gone on to make use of this fact for blending CA with PVDF, which was one of the primary goals of the current invention.

[47] In embodiments of the invention, solvent-processed fabrication of coatings comprising PVDF and CA blends form a polymer matrix with tunable microstructure and hydrophobicity. Application-specific variations in surface wettability and microstructure are achieved by adding functional micro and nano-structured fillers into the polymer blend. The PVDF-CA and PVDF-polyCA blends can be filled with various microfϊllers and/or nanofillers, for example and without limitation, particles of ZnO, TiO₂, Indium Tin Oxide (ITO), SiO₂, single or multi-walled carbon nanotubes (SWCNT or MWCNT), carbon black (CB), hydroxyapatite, clay or various other polymer powder fillers, such as Teflon or polyetheretherketone (PEEK) or polyethylene (PE), for additional functionality (e.g., tuning the surface energy of films from partially hydrophilic to super hydrophobic) and enhanced high temperature resistance. For instance, a coating of a PVDF/CA or PVDF/polyCA blend comprising fillers may exhibit superhydrophobicity. The characteristic "superhydrophobic" may be applied to a material having a static water contact angle greater than 150°. The polymeric composite coatings described herein achieve such high static water contact angles by the presence of a hierarchical roughness structure spanning from micro to nano-scale sizes, along with the presence of the hydrophobic polymer PVDF. Superhydrophobic surfaces over which water contact angles exceed 150° are also considered self-cleaning. Surfaces over which water contact angles are as high as 120° (Teflon, for example) are considered hydrophobic.

[48] It is believed that such novel PVDF-CA and PVDF-polyCA composites can be used as functional and biocompatible coatings in numerous industries, for example and without limitation in microelectronics, fluid power, construction, and medical technology applications. The polymer composites according to embodiments of the invention may be applied as a coating to a substrate in an open-air well ventilated environment, for example, by low-cost methods, such as drop casting, spin coating and spray casting. Any suitable casting equipment may be employed to coat the composite onto a substrate, for example an industrial grade internal mix airbrush atomizer (ANEST IWATA, USA Inc., Westchester, OH). Further, any substrate that is sufficiently clean to allow good adhesion of the coating may be used.

[49] A notable advantage of this coating technique is that it may be performed by a regular spraying process, which is uniquely suited to large area coating applications. In general, this is one of the primary limitations in commercializing technologies for making superhydrophobic surfaces for large area applications. Previously, plasma processing appeared to be the only technique of superhydrophobic surface preparation with potential for large area applications. However, plasma processing is limited by the size of the plasma reactor. Although recently some works have demonstrated the use of scalable spray techniques for making superhydrophobic surfaces, our technique remains unique because the drying stage in our methods occurs at moderate temperatures (i.e., below 130 ⁰C), with drying times on the order of minutes. Even temperatures below 100⁰C can be used when the drying times are extended. Also most of our superhydrophobic coatings are prepared from biocompatible components, which make them uniquely suited for biological applications. These characteristics make the processes very attractive for wide range of industrial applications.

[50] A further significant advantage of the polymeric composites of the present invention is that they are robust. In particular, coatings formed from the composites can withstand mechanical stress and still remain adhered to a substrate and maintain their hydrophobic or superhydrophobic characteristics. In addition, the materials involved in the coatings described herein are fairly inexpensive, making the process scalable and economically feasible. Therefore, these techniques can be developed into versatile, industrially feasible, low cost methods to produce coatings with different surface energies for a broad range of applications.

[51] The following examples are illustrative of embodiments of the present invention, as described above, and are not meant to limit the invention in any way.

EXAMPLES

Example 1

[52] In embodiments of the invention, PVDF/CA solution blends may be prepared in the presence of rosin. For example, CA monomer (2-ethylcyanoacrylate, Sigma-Aldrich, USA) dissolved in MEK was directly blended with rosin (Sigma-Aldrich, USA) stock solution consisting of a 60 wt. % rosin dispersion in isopropyl alcohol/castor oil (7/1 wt.) solvent. When the PVDF solution in DMF was added to the mixture, no spontaneous polymerization of CA monomer was observed. The blends were adjusted such that a PVD F/C A/rosin wt. ratio of 6/3/1 was maintained in solution to ascertain hydrophobic coatings. MEK was added to further dilute the multi-component polymer dispersion and make it suitable for spray coating.

[53] The polymer mixtures prepared in this manner were used to obtain different filler dispersions by adding either dry zinc oxide (ZnO) microparticles (~ 5 μm in diameter, Sigma-Aldrich, USA) or dry (ZnO) nano-powder (~ 70 nm in diameter, Alfa Aesar, Ward Hill, MA) or a commercial surface functionalized ZnO nano-dispersion (NanoTek 50 wt. %, 70 nm, Alfa Aesar, Ward Hill, MA). Surface functionalization of ZnO was achieved by encapsulating the particles with hydrophilic polyhydroxylated macromolecules (i.e., long-chain glycols).

[54] Coatings were spray cast onto substrates using an industrial grade internal mix airbrush atomizer (ANEST IWATA, USA Inc., Westchester, OH). Polished aluminum foil and a highly hydrophilic 2-D yarn fiberglass cloth (BGF Industries, Greensboro, NC) were used as substrates. As discussed further below, the surface functionality of the nanoparticles prior to blending had a profound effect on the wettability and adhesion strength of the resulting coatings.

[55] Referring to Figs. l(a) to l(c), a piece of aluminum foil coated with a film containing 7 wt. % functionalized ZnO nanoparticles dispersed in a CA/rosin (3/1 wt.) solution and without any PVDF is shown in Fig. l(a). The coating was cured at a temperature of ~ 85 ⁰C in open air for 30 minutes, and the coating caused the initially flat foil to coil up. The contraction of the film is believed to be caused by rapid cross-linking of the CA monomer upon thermosetting. The cohesive cross-linking strength of acrylic matrices upon curing can reach ~10 MPa, which may cause the aluminum foil to coil up. CA polymerization cohesive strength is even higher, i.e., ~ 25 MPa, thus causing the film to be stiff and brittle.

[56] For a coating containing PVDF (PVDF/CA/rosin, 5/4/1 wt.), the rollup of the substrate can be largely reduced, as shown in Fig. l(b). The linear PVDF polymer chains can interfere with the CA cross-linking, thus modifying the elastic modulus of the composite. In addition, cross-linking of CA with the PVDF matrix should reduce the PVDF crystallite sizes and increase the inter-crystallite entanglements, causing formation of a rubbery state within the composite. This change in elasticity of the nanocomposite films was studied with the help of measurements presented in Fig. l(c). The change in modulus of elasticity was measured as a function of PVDF/CA blend weight ratio, while the rosin content was ~ 12 wt. % in all cases. An Instron 5540 tensile tester (Instron, Norwood, MA) was used with 400 μm thick cast film specimens. Curves (1), (2), (3) in Fig. l(c) show the elastic modulus of the nanocomposite coatings to increase with concentration of functionalized ZnO nanoparticles in the range 2 to 8 wt. %. Pure CA/ZnO composites (0% PVDF/CA ratio) were very stiff; as PVDF was added and its concentration increased, the modulus of elasticity of the coatings declined by more than 50%. This suggested more flexible composites in the presence of PVDF.

[57] Ultra-high molecular weight polyethylene (UHMWPE), which is widely used as a load- bearing orthopedic implant, has a modulus of elasticity of - 1000 MPa. The PVDF/CA based composites produced here appear to match or exceed the elastic properties of UHMWPE, in addition to being easily solution processable. Figure l(c) also shows the estimated peel strengths of the composite coatings on a polished smooth aluminum surface in curves (V), (T) and (3'). Two separate regions of peel strength are apparent, namely a regime of low sensitivity to PVDF concentration (up to 60 wt. %), and above 60 wt. % a regime of higher sensitivity. Estimated peel strength values of the present composites with less than 60 wt. % PVDF match or exceed commercial aluminum composite panels containing modified polyester/PVDF blends (~ 400 N/m) or PVDF surfaces modified by plasma enhanced graft co-polymerization techniques.

Example 2

[58] Mesh-like fiberglass-based materials have been recently applied as scaffolds for hard- soft interface regeneration in tissue engineering. Surface morphology, mechanical properties and adhesion characteristics of such scaffolds are critical to maintain continuous hard-soft interface regeneration in tissue engineering. The present biocompatible coatings can also be applied onto such scaffolds to induce additional interface functionality, such as porosity control, anti-microbial activity and adhesion strength manipulation. Figure 2(a) shows a SEM image of an uncoated glass fiber having a diameter of about ~10 μm diameter, separated from a hydrophilic fiberglass cloth. The inset in Fig. 2(a) shows a coated fiberglass cloth sample. The SEM image in Fig. 2(b) shows the morphology of the dry ZnO nanopowder-filled PVDF/C A/rosin (wt. ratio of 6/3/1) coating on a glass fiber separated from the yarn. The coating was spray cast on the fiberglass textile and cured at 100 ⁰C for 30 minutes. As illustrated, the coating introduced both micro and nano-scale roughness on the fiberglass substrate, thus rendering the fiber hydrophobic. The detail of the roughness is magnified in the inset of Fig. 2(b).

[59] Morphology of the coating was manipulated by adjusting the weight fraction of the unmodified ZnO nanopowder used. For instance, at ZnO powder concentrations above ~ 9 wt. %, surfaces were superhydrophobic, due to increased surface roughness of the hydrophobic coatings; however, adhesion to the fiberglass cloth decreased considerably. The term "superhydrophobic" as noted above, refers to a material having a static water contact angle of greater than 150°. To increase the porosity of the scaffold, micron sized ZnO (~ 5μm in diameter, Sigma- Aldrich, USA) fillers were used. In Figure 2(c), a SEM image of a microporous PVDF/CA/rosin coating (wt. ratio of 6/3/1) applied over a bundle of glass fibers is shown. A moderate decrease in the hydrophobicity of the coating was observed in this case where micron-sized ZnO fillers were used.

Example 3

[60] To assess the dependence of bonding strength and wettability of the composite coatings to the fiberglass cloth surface under mechanical strain, a horizontal tensile tester (Tinius Olsen Inc., Horsham, PA) was used. The horizontal placement of the cloth into the test section allowed simultaneous sessile water droplet contact angle monitoring on the test surface while the latter was strained. Figure 3 (a) shows the sessile water contact angle change with applied stress for the coatings on fiberglass using unmodified ZnO nanoparticle fillers (ZnO concentrations up to 10 wt. %). The wt. ratio PVDF/CA/rosin was held at 6/3/1 for all coatings in Fig. 3 containing all three of these components. The contact angles appear to stay nearly constant for applied stresses up to 3 kN/m² for all samples. The amount of stress experienced by joints in a human body during normal movement is approximately 1 kN/m², whereas athletes may apply up to about 3 kN/m² of stress on their joints. Consequently, the polymeric composite coatings containing ZnO filler particles remain hydrophobic even under substantial mechanical stress.

[61] Wettability of the coating without PVDF degraded at the lowest threshold stress because this coating was stiff and brittle; this was marked by subsequent precipitous reduction in contact angle. The coatings containing PVDF showed higher contact angles at the lowest stress (practically same as the stress free condition) for the same concentration of ZnO, due to the hydrophobic nature of PVDF, as illustrated by the two curves for coatings containing 6 wt. % ZnO in Fig. 3a. The highest contact angle measured for these coatings was 158°. The coatings containing PVDF showed good durability up to 5 kN/m² even at 10 wt. % ZnO nanopowder concentration. However, due to poor dispersion of ZnO nanoparticles, particularly above 7 wt. % ZnO, the coatings showed signs of flaking and deterioration of contact angle at high stresses.

[62] Figure 3(b) shows the results for fiberglass cloths coated with PVDF/CA/rosin (wt. ratio of 6/3/1) composite containing functionalized ZnO nanoparticles. Wetting of the coated surfaces remained nearly unchanged for stress values up to 15 kN/m² even for 10 wt. % particle loading. This indicates that the coatings withstood higher stress rates without peeling off from the substrate. It is possible that better dispersion of the functionalized nanoparticles within the polymer matrix, as compared to unmodified ZnO, enables efficient polymer chain mobility, hence improving strain resistance. In addition, efficient nanoparticle dispersion within the polymer matrix can transform large PVDF spherulites into thin fiber-like crystallites, thus causing better energy dissipation within the polymer matrix. Better dispersed functionalized nanoparticles decreased coating hydrophobicity, as evidenced by the contact angles in Fig. 3b when compared to those in Fig. 3a, possibly by diminishing hierarchical surface roughness.

Example 4

[63] In a glass flask equipped with a water cooling jacket, CA (ethyl 2-cyanoacrylate (CA) monomer (Sigma- Aldrich, St. Louis, MO) was dispersed in reagent grade MEK (Sigma- Aldrich, St. Louis, MO) such that a 33 wt. % CA in solution was obtained. Using a syringe pump, equal volumes of reagent grade DMF (Sigma- Aldrich, St. Louis, MO) and MEK were slowly introduced into the CA dispersion while stirring continuously such that the final concentration of CA in the multi component solvent system was 8 wt. %. During this process, heating and thickening of the mixture were observed. The final mixture was stored at overnight at room temperature. As noted above, DMF acts as a catalyst in rapid anionic polymerization of CA, however, in a co- solvent system in which the relative amount of DMF in solution is adjusted, the anionic polymerization reaction of CA progresses more slowly. Through such slow polymerization, a polymer having a high degree of polymerization (polyCA) is obtained, resulting in lower residual strain and elevated flexibility in comparison with polymers obtained by rapid polymerization.

[64] Various concentrations of PVDF in DMF solutions were obtained by dissolving PVDF pellets (M_w ~ 530,000 Da) (Sigma-Aldrich, St. Louis, MO) in DMF at 60 ⁰C. The PVDF and polyCA solutions were miscible at any proportion and could be diluted with common solvents such as acetone, MEK, and acetates. The blending of the two polymer solutions was performed at room temperature with slow mixing. The final composition of the blends depended on initial polymer weight concentrations in the solutions and extent of dilution and is reported in the following as a blend ratio (by weight) of PVDF to polyCA. To prepare the dispersion of nanoparticle fillers in the PVDF-polyCA polymer solution, the fillers were added directly and stirred using a vortex mixer without using additional dispersants or surfactants. The resulting dispersions were very stable for the time scale of subsequent coating/casting experiments.

Example 5

[65] Composite polymer films were obtained by drop casting on glass slides and curing at 100 ⁰C. The morphologies of the films were investigated by scanning electron microscopy (SEM). These films were used for subsequent droplet impact tests to evaluate their surface energy. The droplet impact measurements were performed with a set-up described in detail in the following publication: Bayer, LS. and CM. Megaridis, "Contact angle dynamics in droplets impacting on flat surfaces with different wetting characteristics," Journal of Fluid Mechanics, 558: p. 415-449, 2006. [66] In Figs. 4(a)-(d) the change in morphology is shown for a PVDF/polyCA film with a weight blend ratio of 0.25:1 PVDF:polyCA as a function of distance from the edge (i.e., contact line) of the film. Similar variations in the morphology were found for other concentrations as well. The pictures shown in Fig. 4 are SEM images. The image at the film center, Fig. 4(d), reveals a membrane with pore sizes of 2-5 μm in diameter. The micro-porosity of the film decreases from its center to the edge, and ultimately vanishes at the film edge, as shown in Fig. 4(a). Without wishing to be bound by theory, it is believed that this morphological change is related to the change in the film thickness from center to edge, and can be explained using the schematic shown in Fig. 5, as follows.

[67] In the schematic of Fig. 5, the respective locations for the SEM images (a) through (d) in Fig. 4 are indicated with respect to the size of the drop cast film. This schematic can help in understanding the changing morphological structure of the film with distance from the edge. CA has strong affinity for moisture. Therefore, traces of moisture on the substrate surface should trigger immediate cross-linking of polyCA chains, as denoted by reference number 2 in the schematic in Figure 5, and cause improved adhesion of the film. The polyCA should also cross-link at the upper surface of the film, where it is exposed to the ambient moisture. This will cause formation of a dense polyCA network in the exposed parts of the film. This network will surround the remaining PVDF and hinder the growth of porous structure there.

[68] The situation is very different toward the thick center of the film. Here, the cross- linking of the polyCA will be restricted to the surface of the film and rapid evaporation of the solvents during curing will increase the concentrations of the polyCA and PVDF. . Gradually, the evaporation of the solvents would cause a phase separation of solid polymer out of the polymer solutions and thus formation of strands of PVDF, in a manner similar to a phase inversion mechanism. Interconnected strands of PVDF are indicated by reference number 4 in Fig. 5, while PVDF spherulites are indicated by reference number 6 in the same figure.

[69] The slow removal of DMF, which has a higher boiling point than MEK, allows enough time for the crystallization of PVDF in the strands, as demonstrated by the XRD results presented in Fig. 6 for the 0.25:1 PVDF/polyCA blend. The XRD plots in that figure show a clear peak at about 20° for the center of the film, marked by reference number 11, which indicates the presence of α-phase PVDF. Line 13 is the result for a location before the center, while line 15 is the result for a location before the edge and line 17 is the result for a location at the edge. Closer to the edge of the film, the peak diminishes in size and a flatter profile indicates a gradual loss of crystalline character. The presence of significant reading at other angles in the neighborhood indicates presence of amorphous polyCA almost throughout the film.

Example 6

[70] Referring to Figs. 7 and 8, the results of water droplet impact on the PVDF/polyCA drop cast composite films are presented. The impact Weber numbers, ("We"), were 11 and 14, respectively. The two values of the We are in the range that should produce droplet spreading/receding on the partially wettable to non-wettable surfaces that are considered here. The drop impact for each Weber number was performed on three different films with different blend ratios of PVDF to polyCA (0.25:1 by wt., represented by stars, 0.5:1 by wt., represented by circles, and 1 :1 by wt., represented by triangles, in Figs. 7 and 8).

[71] The scales chosen for dimensionless quantities were as follows: The initial droplet diameter was used for normalizing the values of contact line diameter (D), while the time to reach maximum lateral spread was used to normalize time (t). Figures 7(a) and 8(a) show the spreading stage, whereas Figs. 7(b) and 8(b) show the receding stages of the droplet impact events. The spreading regimes in Figs. 7(a) and 8(a) are dominated by inertia forces and result in spreading of the droplets to a maximum diameter that is primarily a function of We and surface wettability. The receding phases of Figs. 7(b) and 8(b) seem to have abrupt jumps in the contact line diameters, especially on the film with 0.5:1 wt. ratio. A careful examination of this stepped variation indicates that it resembled "stick-slip" motion of the droplet contact line. This is a very common phenomenon observed in droplet impact studies on heterogeneous surfaces and can be understood as follows: In the receding phase the kinetic energy of the droplet is lower than during initial spreading, and the surface tension effects become pronounced. The droplet impact tests of this example were performed away from the edge of the films, where the film consists of a heterogeneous mixture of PVDF and polyCA, as corroborated by the XRD measurements of Fig. 6. Thus, the resulting stick-slip motion during the receding stage of contact line motion is not surprising. It is most pronounced for the blend with an intermediate wt. % of the two polymers involved, which possibly resulted in a film surface with high heterogeneity.

Example 7

[72] In Fig. 9 the temporal change in apparent dynamic contact angle for water droplet impact on the PVDF/polyCA films is presented. Only impacts with We ~ 11 on each of two films (blend wt. ratios 0.25:1, represented by stars, and 0.5:1, represented by squares) are shown; the measurements for other We were similar due to close We values. The equilibrium contact angles of 60° and 70° for the two tests in Fig. 9 suggest that these films are partially wettable in nature. The dynamic contact angle variation shown in Fig. 9 is typical of partially wettable surfaces except in the receding phase of the contact line motion for t ~ 1 to 5. The receding phase is marked by more rapid changes in the dynamic contact angle, which reflects a competition between the capillary forces and contact line friction, which is enhanced by the surface heterogeneity, especially for the second film, which has a blend wt. ratio of 0.5:1 PVDF to polyCA.

Example 8

[73] Figure 10 presents the change in surface energy of the PVDF/polyCA composite films as function of the blend ratio of the two polymers. The surface energy was estimated using the acid-base method, as described in connection with different polymeric surfaces in the following publication: Bayer, I. S., CM. Megarids, J. Zhang, D. Gamota, and A. Biswas, "Analysis and surface energy estimation of various model polymeric surfaces using contact angle hysteresis," Journal of Adhesion Science and Technology, 21(15): p. 1439-1467, 2007. The surface energy of a surface is a measure of its adhesion, and the higher the surface energy, the better is its adhesion quality. As is evident from Fig. 10, the surface energy of the PVDF/polyCA films decreases with increasing concentration of the PVDF in the blends.

Example 9

[74] The effects on physical properties of PVDF/polyCA composites of adding fillers were tested. Organic/inorganic hybrid nanocomposites based on the PVDF/polyCA polymer blend matrix were fabricated by dispersing clay (kaolinite), ZnO nanoparticles, and/or TiO₂ nanoparticles in the PVDF/polyCA solution. Two different procedures were followed in introducing ZnO nanoparticles to the polymer matrix. The first was mechanical dispersion of ZnO dry nano-powder (Alfa Aesar, Ward Hill, MA) with a 60 nm average particle size in the polymer solution with a vortex stirrer. The second technique involved blending a commercial ZnO acetate-based colloidal dispersion (Alfa Aesar, Ward Hill, MA) with the PVDF/polyCA polymer solution. The multi- component slurries were then spray coated on aluminum substrates. In order to improve substrate adhesion of the PVDF/PolyCA composites, a tackifying resin (i.e., gum rosin) was introduced as a powder to the polymer blends in solution. In coatings containing both clay and ZnO fillers, the best dispersion was achieved when rosin was also present.

[75] TiO₂ particles were introduced from a separate colloidal dispersion prepared according to the method disclosed in the following publication: Conley, R.F., Practical dispersion, New York: Wiley- VCH, p.201, 1996. The dispersion formulation was adjusted with the help of surfactants and plasticizers in such a way that it could form high-solid content conformal coatings. Table I shows the compositional details of the solvent-based TiO₂ suspension. Table I: Compositional details of the solvent-based TiO₂ suspension.

Ingredient wt. % Function Origin

Hexamethyldisiloxane 32 Solvent/dispersant Sigma- Aldrich, St. Louis, MO

Terpene 16 Solvent (Cyclosolv™, T2 Laboratories Inc., Jacksonville, FL)

Poly(isobutyl methacrylate) 7 Film forming agen

Dibutyl phthalate 2 Plasticizer Sigma- Aldrich, St. Louis, MO

TiO₂ 42 Filler (Ti-Pure^® R-902+ rutile, DuPont, Edge Moor, DE)

Sodium dioctyl

1 (Octowet 70 MS, Tiarco

Surfactant sulfosuccinate Chemical, Dalton, GA)

[76] The colloidal dispersion was miscible with the PVDF/polyCA solution at any proportion. The level of hydrophobicity of the surfaces of the resulting film coated and cured on a substrate as a function of nano-particle inclusion was characterized by means of static contact angle measurements, and the morphologies of these coatings were investigated by SEM.

[77] Referring to Fig. 11, SEM images are provided of spray coatings of PVDF/polyCA blends containing ZnO nanoparticle filler. The coatings possesses the hierarchical roughness structure that changes from micro-roughness to nano-roughness, as is evident from the images in Fig. 11, which were taken at increasingly higher magnifications from 11 (a) to l l(d). The two-polymer blend on its own (i.e., in the absence of any filler) has a tendency to nucleate collectively with the evaporation of the solvents and form a micro-scale morphological structure seen in the SEM images of Fig. 4. However, the presence of nanoparticle fillers at high concentration, such as about ~ 9 wt. %, provides nucleation sites for the polymer phases coming out of the solution due to solvent removal. This nucleation phenomenon results in the formation of a nanocomposite, as illustrated by Fig. l l(d). The static contact angle of a sessile water droplet on this coating was measured to be about 155°. This superhydrophobicity of the sprayed coating can be explained by the presence of a hierarchical roughness structure spanning from micro to nano-scales, along with the presence of the hydrophobic polymer PVDF. The presence of polyCA improves the adhesion property of these coatings.

[78] Figure 12 shows surface morphology of clay- and ZnO-fϊlled PVDF/PolyCA nano- porous composite surfaces including the gum rosin tackifier. ZnO in the composite was introduced from a commercial colloidal dispersion. Similar to Fig. 11, the SEM images of Figs. 12(a) to 12(d) were taken at increasingly higher magnifications. Fig. 12 shows that both clay and ZnO fillers are well dispersed within the multi-component polymer matrix. The arrows denoted by reference numbers 21, in Fig. 12(c), and 23, in Fig. 12(d), point out kao unite (clay) platelets.

Example 10

[79] Figure 13 shows a time sequence of images depicting a bouncing water droplet upon impact on a superhydrophobic nanocomposite surface. This particular water-repellent nanocomposite substrate is the ZnO-filled PVDF/polyCA composite prepared by direct mixing of ZnO nanopowder and shown in the SEM images of Fig. 11. It was found that the degree of water-repellency was dependent on the amount of ZnO added to the blend. Specifically, Fig. 14 shows the change of apparent static water contact angle as a function of weight percent of added ZnO nanopowder. These apparent contact angle measurements were performed a few days after the preparation/curing of the coatings. It was discovered that for any specific ZnO nanofiller concentration, a slight decrease in apparent water contact angle (~ 10°) was observed a few days following curing, as compared to the value obtained immediately after the curing process. After this small initial decrease, the water sessile contact angle was found to remain practically unchanged for a few weeks. In spite of such minor changes in apparent contact angles, at or above ~ 8 wt. % ZnO, the nanocomposite surfaces remained highly water- repellent.

[80] In contrast, nanocomposite surfaces fabricated using the pre-dispersed ZnO suspension were not highly water repellent (not shown). Apparently, the degree of dispersion of the nanoparticles has a direct influence on surface morphology. For the given PVDF/polyCA polymer system, formation of hierarchical hydrophobic surface morphology, a necessary condition for water repellency, was obtained by introducing ZnO nanoparticles directly rather than in pre-dispersed form. However, a uniform surface porosity was formed more readily when ZnO was added from a solution-based colloidal dispersion. Therefore, by appropriately choosing the type of nanofillers and their concentrations, the coating properties may be tailored towards specific industrial applications.

Example 11

[81] As noted above, an alternative co-solvent based technique to control the polymerization reaction of cyanoacrylates (CA) was developed. This technique eliminates the need for cooling, which is typically used to remove the heat generated by exothermic polymerization of CA in the presence of DMF. In such embodiments, boiled linseed oil (BLO), a common drying oil frequently used in woodworking as a water and oil resistant coating, is incorporated in the solvent blend.

[82] The following steps were used to prepare the polymerized CA solution, which could then be used for preparing nanocomposite coatings: Three grams of CA monomer was added to 20 ml methyl ethyl ketone (MEK) and stirred. Next, 3 ml BLO was added drop wise to the monomer solution, and stirred. This led to a visible thickening of the solution, indicating CA polymerization. Two ml DMF was then added slowly to the obtained thick solution in order to catalyze the polymerization reaction to full completion. A slight temperature increase during the polymerization process was observed, of about 5-10 ⁰C, however, it was negligible compared to temperature increases during direct catalytic polymerization of CA monomer with DMF which can be up to 70 ⁰C. Accordingly, no external cooling was required. The obtained solution was allowed to cool down to room temperature, a process that never took more than 15 minutes. The polymerized CA solution was then diluted with MEK and mixed with PVDF in DMF solution to form PVDF/polyCA polymer blends.

[83] Functional filler particles could also be dispersed in the polymer blend for obtaining coatings with tunable hydrophobicity and adhesion strength. The prepared multi- component mixtures were spray cast on various substrates and cured at 130 ⁰C for 30 minutes to form nanocomposite coatings. These coatings displayed superior substrate adhesion compared to coatings obtained using direct DMF catalyzed CA/PVDF blends. This technique may be employed with fillers such as microparticles or nanoparticles of ZnO, TiO₂, Indium Tin Oxide (ITO), SiO₂, single or multi-walled carbon nanotubes (SWCNT or MWCNT), carbon black (CB), hydroxyapatite, clay or various other polymer powder fillers, such as Teflon or polyetheretherketone (PEEK) or polyethylene (PE).

Example 12

[84] The effect on coating surface wettability of various fillers was investigated by preparing coatings comprising solution blended PVDF and polymerized ethyl cyanoacrylate (PECA) blends and containing fillers of different sizes and blends. All PECA solutions for these experiments were prepared using the method of Example 4. The fillers were added directly into the blends of the two polymer solutions. Individual polymer solutions were prepared separately to obtain 20 wt. % PVDF dissolved in DMF, and 8 wt. % PECA dissolved in a mixture of DMF and acetone. The coatings were prepared by spray casting a dispersion of filler particles in polymer blends; the dispersion was further diluted with acetone to achieve sprayability on high strength grade aluminum foil. The spraying was performed using a Paasche VL siphon feed airbrush (Paasche Airbrush Company, Chicago, IL). The coated foils were heated at 125°C for 45 minutes to cure the coatings and remove any solvents. All dispersions comprised PVDF and PECA in 60:40 weight ratio to ensure proper particle dispersion and good adhesion of the resulting coatings. To study the effect of fillers on coating wettability, the concentrations of the polymers were kept constant. Typically 18 grams of polymer/filler/solvents mixture (dispersion) was used to spray a 10-inch x 10-inch square of aluminum foil; the relative weight of the different components in the standard dispersion is shown in Table 2 below. Table 2: Composition of the standard dispersion used to make coatings

Amount present in 18 g

Ingredient wt. % dispersions (g)

20% PVDF by wt. dissolved in DMF 1.5 8.3

8% PECA by wt. dissolved in DMF/acetone 2 .5 13.9 mixture

Filler particles 0.36 - 3.6 2 - 20

Acetone 13.64 - 10.4 75. 8 - 57. 8

[85] Three different types of particle fillers were used to demonstrate the versatility of the PVDF/PECA blends in dispersing functional filler particles of different sizes (micro/nano) and surface energy (hydrophilic to hydrophobic). The fillers were poly(tetrafluoroethylene) (PTFE) microparticles (~ 1 μm in diameter) and ZnO microparticles (~ 5 μm in diameter) obtained from Sigma-Aldrich, USA, and ZnO nanoparticles (~ 40-100 nm in diameter) obtained from Alfa-Aesar, USA. PTFE particles are hydrophobic, whereas both micro and nano-size ZnO particles should be hydrophilic, as they were not functionalized in any way. The wettability of the coatings was tested using sessile droplet contact angle measurements for water and also water + isopropyl alcohol (IPA, 2-Propanol) mixtures in a 90:10 weight ratio. This latter mixture should have a surface tension of 40.42 mN/m and serves as a measure to determine the alcohol repellency of the present coatings. The requirement of water repellency is of great importance for large area coating of medical fabrics, for instance. In addition, repellency of such a low surface tension liquid is a more severe test for the surface energy of coatings and, in general, very challenging to achieve for large area coating applications. It should be mentioned here that these coatings consist of biocompatible components, which combined with their alcohol repellency could be especially well suited for medical applications.

[86] The addition of particles is expected to influence the wettability of the resulting coatings by two different mechanisms. On one hand, it should influence the surface roughness of the coatings, which can change the contact angle of liquid drops present on the surface (the Wenzel effect), and on the other hand, it can influence surface energy of the coating depending on the surface energy of the particles (i.e., hydrophilic or hydrophobic). For each type of filler particles used here, particle amounts were added ranging from the low to the maximum possible limit to obtain the entire range of wettability obtainable by adding these fillers to PVDF/PECA blends.

[87] In Figs. 14 through 18, the water contact angle is marked as "WCA" and the contact angle for water + IPA mixture droplet is marked as "WICA". It was observed that at sufficiently high content of each type of filler particles, the WCA for the coatings approached or exceeded 150 degrees, which is considered a threshold value for a coating to be superhydrophobic. Contact angle by itself, however, is not a sufficient measure of the superhydrophobicity of a surface. Contact angle hysteresis, or roll-over angle of a liquid droplet on a coated surface, is an additional quantity necessary to quantify the level of superhydrophobicity. Roll-over angle can be measured by letting a liquid droplet roll over a pre-inclined coated surface or by increasingly inclining a coated surface with a sessile droplet sitting on top of it. The measurements described herein were performed with the latter technique. The coated aluminum foil pieces were cut and pasted on a tilt stage, having angle measure accuracy (graduation) of 1 degree. After a sessile droplet was gently placed on the coated foil, the stage was inclined steadily until the droplet rolled over. These roll-over angles are reported as water sliding angle ("WSA") and water + IPA sliding angle ("WISA") in Tables 3-6. The entry "stick" in the Tables indicates that a droplet did not slide at all.

Table 3: Sliding angles for liquid droplets on coatings containing PTFE filler particles. Two sliding angle measurements were performed for each liquid. The error column represents the error originating from angular graduation on the tilt stage used in this study.

PTFE WSAl WSA2 Avg. Err. WISAl WISA2 Avg. Err.

Content (%) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.)

2 Stick Stick - ±1 Stick Stick - ±1

4 40 30 35 ±1 Stick Stick - ±1

6 7 11 9 ±1 Stick Stick - ±1

8 6 8 7 ±1 Stick Stick - ±1

10 4 2 3 ±1 58 80 69 ±1

12 2 2 2 ±1 24 22 23 ±1

14 2 2 2 ±1 16 10 13 ±1

16 2 2 2 ±1 16 12 14 ±1

20 2 2 2 ±1 12 8 10 ±1

Table 4: Sliding angles for liquid droplets on coatings containing ZnO filler microparticles. Two sliding angle measurements were performed for each liquid. The error column represents the error originating from angular graduation on the tilt stage used in this study. μ ZnO WSAl WSA2 Avg. Err. WISAl WISA2 Avg. Err.

Content (%) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.)

2 Stick Stick - ±1 Stick Stick - ±1

4 Stick Stick - ±1 Stick Stick - ±1

6 10 24 17 ±1 Stick Stick - ±1

8 10 12 11 ±1 Stick Stick - ±1

10 Stick Stick - ±1 Stick Stick - ±1 Table 5: Sliding angles for initially sessile liquid droplets on coatings containing PTFE micro particles and ZnO nanoparticles as fillers. The two types of particles were added in 50:50 wt. ratio and their combined weight was used to calculate the percentage of filler content listed in the first column. Two sliding angle measurements were performed for each liquid. The error column represents the error originating from angular graduation on the tilt stage used in this study.

(PTFE + WSAl WSA2 Avg. Err. WISAl WISA2 Avg. Err. nano ZnO) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) Content (%)

2 Stick Stick - ±1 Stick Stick - ±1

4 Stick Stick - ±1 Stick Stick - ±1

6 6 6 6 ±1 Stick Stick - ±1

8 6 4 5 ±1 Stick Stick - ±1

10 12 10 11 ±1 Stick Stick - ±1

12 6 8 7 ±1 Stick Stick - ±1

14 6 10 8 ±1 Stick Stick - ±1

16 2 4 3 ±1 Stick Stick - ±1

Table 6: Sliding angles for liquid droplets on coatings containing both micro and nanoparticles of ZnO as fillers. The two types of particles were added in 50:50 wt. ratio and their combined weight was used to calculate the percentage of filler content listed in the first column. Two sliding angle measurements were performed for each liquid. The error column represents the error originating from angular graduation on the tilt stage used in this study.

(Micro + WSAl WSA2 Avg. Err. WISAl WISA2 Avg. Err. nano) ZnO (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) (deg.) Content (%)

2 Stick Stick - ±1 Stick Stick ±1

4 Stick Stick - ±1 Stick Stick ±1

6 Stick Stick - ±1 Stick Stick ±1

8 Stick Stick - ±1 Stick Stick ±1

10 86 40 63 ±1 Stick Stick ±1

12 10 8 9 ±1 Stick Stick ±1

[88] Referring to Fig. 15, the WCA and WICA variation with respect to content of hydrophobic PTFE microparticles (~ 1 μm in diameter) are shown. Addition of PTFE particles should increase the surface roughness of the coatings and also lower the overall surface energy of the coating, making it difficult to wet. This results in gradual increase in contact angle of both water and water + IPA mixture droplets reaching a maximum of 164 and 150 degrees, respectively, at 20% PTFE content. The sliding angle variation for these coatings, presented in Table 3 above, also shows a gradual reduction and reaches minimum values of 2 and 10 degrees, for water and water + IPA, respectively. Note that water + IPA mixture drops require much higher content of PTFE for sliding due to the much lower surface tension 40.42 mN/m of this liquid mixture.

[89] Figure 16 shows the WCA and WICA variation with addition of hydrophilic ZnO microparticles (~ 5 μm in diameter). Addition of hydrophilic microparticles should increase the surface roughness of the coatings, but increase the overall surface energy of the coating. These two effects are in competition with each other. Therefore, although there is a rise in contact angle for both liquids with addition of ZnO microparticles, the rise in contact angle slows down from 6% and higher particle concentrations (see, especially WICA variation in Fig. 16). The competing effects of increase in coating surface energy and increasing surface roughness due to increasing ZnO microparticle content is more apparent from Table 4, which shows sliding angle for water and water + IPA drops on these coatings. The water + IPA drops never slide no matter what the particle content. The water droplets do slide for intermediate ZnO microparticle content because the surface roughness effects dominate over surface energy, however, they remain stuck at 10% particle content where the surface energy effect starts to dominate.

[90] Referring again to Fig. 14, the change in WCA and WICA with addition of hydrophilic ZnO nanoparticles (~ 40-100 nm in diameter) is shown. Addition of nanoparticles will increase the fine surface roughness of the coatings, but the surface roughness increase should be lower than that for the same content of microparticles. However, the change in overall surface energy of the coating is expected to be similar. This is apparent from the leveling off of WCA in Fig. 14. The WICA shows initial increase followed by a clear decrease in the contact angle. This indicates that in the beginning the increase in surface effect dominates, but then it gives in to the increase in coating surface energy due to addition of hydrophilic ZnO nanoparticles. The sliding angle measurements showed both types of droplets remaining stuck on the plate for all different ZnO nanoparticle content shown in Fig. 14 and therefore the corresponding table is not shown for the sake of brevity.

[91] Referring to Figs. 17-18, the results showing the effect of adding both micro and nanoparticles are presented. This should result in hierarchical micro/nanoscale surface roughness morphology, which is essential to obtain superhydrophobic surfaces. In Fig. 17, the change in WCA and WICA with addition of PTFE micro (~ 1 μm in diameter) and ZnO nanoparticles (~ 40-100 nm in diameter) is shown. The two types of particles are used in 50:50 wt. ratio with respect to each other and their overall content in dispersion is plotted along the abscissa of Fig. 17. Note that for 2% PTFE + nano ZnO content the WCA is 134 degrees, whereas the corresponding WCA for 2% pure nano ZnO is 99 degrees (see Fig 14) and for pure PTFE microparticles 95 degrees (see Fig. 15). This suggests the importance of hierarchical surface morphology resulting from addition of both micro and nanoparticles. At low ZnO content (e.g., 2%), the well- dispersed nanoparticles would get almost entirely buried in the polymer matrix of the coatings and thus the effect of particle functionality (hydrophilicity) is not as clear at such low particle content, and consequently surface roughness effects dominate. This can help in understanding the slightly higher WCA value for pure ZnO nanoparticles compared to pure PTFE microparticles for 2% particle content, although the former are hydrophilic. The effect of the presence of hydrophilic ZnO nanoparticles in these coatings, however, becomes much clearer through the sliding angle measurements shown in Table 5. Here, it is shown that water + IPA mixture drops (low surface tension) never slide. On the other hand, water droplets slide at 6% and higher particle content.

[92] Figure 18 shows the contact angle variation for coatings containing both micro (~ 5 μm in diameter) and nanoparticles (~ 40-100 nm in diameter) of ZnO. The trends appear to be very similar to those of Fig. 14. Here as well, a key difference appears in sliding angle measurements shown in Table 6. Water drops do slide at high particle contents (10 and 12%), whereas the water + IPA drops never slide. Note that for these fillers 12% was the highest particle amount that could be dispersed in PVDF/PECA blends prepared here.

Example 13

[93] The coatings disclosed herein may be used in combination with other materials to provide multiple benefits, such as by providing one layer of a multilayer coating. For instance, to seal an aluminum reservoir containing acetonitrile, a coating comprising PVDF, PECA and nanoparticles was applied over a layer of a thermoplastic polymer (i.e., polyethylene) adhered to the aluminum. The application of the PVDF-based coating can be performed with any suitable method, such as a capillary bridge based printing method, and any number of thin films of the coating may be applied to provide a total PVDF-based coating thickness between about 20 microns and several hundred microns. Next, the PVDF-based nanocomposite coating was allowed to dry at 50 ⁰C for one hour.

[94] Following 24 hours at room temperature, the acetonitrile solvent remained enclosed in the reservoir. Thus, the polyethylene exhibited good adhesion to the aluminum substrate and containment of the acetonitrile. The PVDF-based nanocomposite coating provides a durable, chemically-inert and mechanically strong exterior surface to protect the polyethylene and acetonitrile from environmental and weather conditions such as UV radiation, rain, wind, abrasion, etc. For instance, the two-layer coating exhibits a negligible water vapor transmittance due to the superhydrophobic nature of the PVDF- based coating. Consequently, the PVDF-based coating may be used as part of a multilayer coating in contact with liquids and effective to seal liquids within containers.

[95] While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. Variations and modifications of the foregoing are within the scope of the present invention. It is also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.

Claims

WE CLAIM:

1. A polymeric composition comprising a blend of poly(vinylidine fluoride) (PVDF) and at least one cyanoacrylate (CA).

2. The composition of claim 1, further comprising rosin.

3. The composition of claim 1, wherein at least one CA is provided by a solution comprising a CA polymer.

4. The composition of claim 3, wherein the CA polymer is an ethyl 2-cyanoacrylate polymer and the solution comprises a co-solvent blend comprising methyl ethyl ketone (MEK) or acetone and dimethylformamide (DMF).

5. The composition of claim 1, further comprising a filler comprising at least one nanoparticle, at least one microparticle, or combinations thereof.

6. The composition of claim 5, wherein the filler comprises at least one non-functionalized particle, at least one surface-functionalized particle, or combinations thereof.

7. The composition of claim 5, wherein the filler is selected from the group consisting of at least one particle of layered silicate, zinc oxide, titanium oxide, indium tin oxide, silica, single or multi-walled carbon nanotubes, carbon black, teflon, polyetheretherketone (PEEK), polyethylene (PE) or combinations thereof.

8. The composition of claim 5, wherein the filler has an average diameter in the range of 1 nanometer to 100 microns.

9. The composition of claim 1, further comprising boiled linseed oil.

10. The composition of claim 1, wherein the composition is a film having a hierarchical surface roughness comprising both a microscale structure and a nanoscale structure.

11. The composition of claim 1 , wherein the weight ratio of the PVDF to the at least one CA is in the range of 60:40 to 70:30.

12. A method for making a polymeric film comprising:

a. providing a composition comprising poly(vinylidine fluoride) (PVDF) and at least one cyanoacrylate (CA);

b. coating the composition onto a substrate; and

c. curing the composition to form the polymeric film on the substrate.

13. The method according to claim 12, wherein the substrate comprises a rigid or flexible material

14. The method according to claim 12, wherein the composition is coated onto the substrate in ambient air.

15. The method according to claim 12, wherein the curing comprises heating the composition coated on the substrate at a temperature of at least 50 degrees Celsius for at least 30 minutes.

16. The method according to claim 12, wherein the composition is coated onto the substrate using a method selected from the group consisting of spray casting, drop casting, dip coating and spin coating.

17. The method according to claim 12, wherein the film has a surface energy of less than 32.5 mJ/m².

18. The method according to claim 12, wherein the CA polymer is an ethyl 2-cyanoacrylate polymer prepared by adding a ethyl 2-cyanoacrylate monomer to a co-solvent blend comprising methyl ethyl ketone (MEK) or acetone and dimethylformamide (DMF).

19. The method according to claim 12, wherein the composition further comprises rosin.

20. The method according to claim 12, wherein the composition further comprises boiled linseed oil.

21. The method according to claim 12, wherein the composition further comprises a filler comprising at least one nanoparticle, at least one microparticle, or combinations thereof

22. The method according to claim 12, wherein the film has a water sessile droplet contact angle of at least 80°.

23. The method according to claim 21, wherein the film has a water sessile droplet contact angle of at least 150°.