CA2013691A1 - Methods and devices for detemining the contact angle of a drop of liquid placed on a substrate - Google Patents
Methods and devices for detemining the contact angle of a drop of liquid placed on a substrateInfo
- Publication number
- CA2013691A1 CA2013691A1 CA002013691A CA2013691A CA2013691A1 CA 2013691 A1 CA2013691 A1 CA 2013691A1 CA 002013691 A CA002013691 A CA 002013691A CA 2013691 A CA2013691 A CA 2013691A CA 2013691 A1 CA2013691 A1 CA 2013691A1
- Authority
- CA
- Canada
- Prior art keywords
- substrate
- drop
- rays
- diffusing
- receiving surface
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/02—Investigating surface tension of liquids
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/02—Investigating surface tension of liquids
- G01N2013/0208—Investigating surface tension of liquids by measuring contact angle
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N13/02—Investigating surface tension of liquids
- G01N2013/0241—Investigating surface tension of liquids bubble, pendant drop, sessile drop methods
Abstract
ABSTRACT OF THE DISCLOSURE
The invention relates to improvements to methods and devices for determining the contact angle of a drop of liquid placed on a substrate. The device comprises : a support 12 for a substrate 11 which receives a drop of liquid 9; a light source 1; optical means, formed for example by a plate with parallel faces 21 rotatable about its axis 22 and whose inclination with respect to the axis may be modified, with a reflecting prism 5a, for forming a primary beam 6a, advantageously annular, striking the interface 8 between drop and substrate; a receiving surface 13a, 13b formed by a reflection diffusing surface;
a reflecting surface 17; and a camera C.
The invention relates to improvements to methods and devices for determining the contact angle of a drop of liquid placed on a substrate. The device comprises : a support 12 for a substrate 11 which receives a drop of liquid 9; a light source 1; optical means, formed for example by a plate with parallel faces 21 rotatable about its axis 22 and whose inclination with respect to the axis may be modified, with a reflecting prism 5a, for forming a primary beam 6a, advantageously annular, striking the interface 8 between drop and substrate; a receiving surface 13a, 13b formed by a reflection diffusing surface;
a reflecting surface 17; and a camera C.
Description
2~ 3~
Improvements to methods and devices for determin~n~ the contact angle of a drop of liquid placed on a substrate.
The present invention relates to the measurement of 5 the contact angle of a drop of liquid placed on a horizontally disposed solid or liquid substrate .
From the value of the contact angle between a drop of liquid and the horizontal surface of a substrate which carries the drop certain properties of the substrate can lO be derived, particularly its wettability and its surface condition, properties which are useful in fundamental or applied research.
The French patent 2 574 180 of the Centre National de la Recherche Scientifique, which recalls the main 15 applications of contact angle measurement, describes a method and device for determining the contact angle of a drop of liquid placed on a horizontal solid or liquid substrate, in which a primary beam of parallel light is directed 20 perpendicularly to the substrate for illuminating a zone of the assembly formed by the drop of liquid and the horizontal substrate (which zone includes the interface between the periphery of the drop and the substrate) while producing a secondary beam by interaction with the drop 25 and the ~ubstrate, and the extent of the illumination transition presented by the secondary beam in correspondence with the periphery of the drop is measured on a receiving surface intercepting this secondary beam.
However, the method and device of the above patent, which generally yives satisfactory results in the case of v~sual observation of the receiving surface, which is then a frosted surface, do not allow precise measurements to be made for all the drop-substrate pairs in the case of using a camera for displaying the illumination transition, in particular when the contact angle between the drop and the surface of the substrate is relatively high, for example close to 45~, and/or when the substrate is very diffusing.
In fact, although $n the case, illustrated in figure 1, of a low contact angle, it i~ possible with a device of 5 the type described in the above patent 2 574 180, to replace visual examination by a photographic image taken by a camera C, it is no longer the same in the case, illustrated ~n figure 2, of a contact angle close to 45, for the following reason.
Figures 1 and 2 reproduce substantially figure 8 of the above patent, but simplifying it.
In these figures l and 2, there have been designated:
by 1 a laser emitting a beam 2 of horizontal and 15 parallel rays, by 3 an afocal optical system widening beam 2 into a more extensive beam 4, but also formed of horizontal and parallel rays, this afocal optical system being shown solely in figure 1 which illustrates a plano-concave lens 20 3a and a plano-convex lens 3b, by 5 a reflecting mirror, slanted by 45 with respect to the vertical, which produces the primary beam 6 of parallel light, vertical in direction, which illuminates on the assembly to be observed a zone 7 which includes the interface between the periphery 8 of drop 9 and the horlzontal surface 10 of substrate 11, which is for example solld, carried movably by a sample-holder 12, and by 13 a receiving surface interceptin~ the secondary 30 beam 14 resulting from the interaction of the pr~mary beam wlth the drop 9 and substrate 11.
In figures l and 2 have been shown, specially in the primary ~ and secondary 14 beams, the rays directed to and coming from the perlphery 8 of drop 9, namely from the 35 drop-substrate interface, the angle of these rays 14 of the secondary beam with respect to the vertical, so with 2~ J_ the corresponding rays 6 of the primary beam, being twice (2~) the drop-substrate contact angle referenced~.
Although a camera C may, in the case of figure 1 where the contact angle ~ is relatively small (for example 5 not exceeding 10 to 20), receive a large part of the rays such as 15 from the receiving surface 13 and corresponding to the rays 14 of the secondary beam from the periphery 8 of drop 9, it ls no longer the same $n the case of figure 2, where the contact angle ~' is relatively close to 45, 10 for example about 40 and so the angle 2~' about 80, for then camera C recelves practically no rays 15' from the receiving surface 13 and corresponding to the rays of the secondary beam 14 from the periphery 8 of drop 9.
Consequently, although the illumination transition 15 corresponding to the periphery 8 of drop 9 can be readily detected by camera C in figure 1 which receives numerous rays from surface 13, on the other hand observation of this transition is difficult using camera C of figure 2 which receives very few rays from this surface 13.
In order to observe the illumination transition corresponding to the periphery of the drop under excellent conditions, using a camera, even for a relatively high contact angle which may reach about 45, in accordance wlth ~he invention, the surface receiving the secondary 25 beam i8 formed by a reflection dlffusing surface and a reflecting surface is disposed for reflecting the light from this receiving surface towards the camera, so as to concen~rate on the ob~ective of the latter at least the ma~ority of rays form~ng the secondary beam and 30 corresponding par~icularly to the periphery of the drop.
The object of the lnvention is first of all to provide a method for determining the contact angle of a drop of li~uid placed on a substrate, for any contact angle less than 45~, which consists in directing 35 perpend~cularly to the substrate a primary beam of parallel light for illuminating a zone which contains the 2 a ~
interface between the periphery of the drop and the substrate, determlning the illumination transition zone presented by a secondary beam resulting from the interaction of the primary beam with the drop and the substrate, on at least one receiving surface lntercepting this beam, and is characterized in that said receiving surface is a reflection diffusing surface, in that a reflecting surface is provided disposed inside said diffusing receiving surface for reflecting the light rays from said diffusing receiving surface, and in that the rays reflected by said reflecting surface are collected by a camera.
The invention also has as object a device for implementing the above method, comprising a support for holdin~ a substrate horizontal on which is placed a drop of liquid, a light source associated with optical means for forming from the light source a primary beam of parallel light directed perpendicularly to the substrate, at least one receiving surface surrounding the substrate for intercepting the returning secondary beam producsd by interaction of the primary beam with the drop and the substrate, and is characterized ln that said receiving surface is formed by a reflection diffusing surface, in that a reflecting surface is disposed inside said diffusing receiving surface for reflecting the beam of rays reflected by said diffusing receiving surface and in that lt comprises a camera disposed for collecting the rays reflected by said reflecting surface.
The invention will in any case be well understood from the following complement of descript~on and the accompanying drawings, which complement and drawings are of course given by way of example.
Figures 1 and 2, already described above, illustrate schematically the problems arising from the use of a 3~ dsvice accordin~ to figure ~ of the above mentioned French patent when it is desired to use a camera for observing 2~t3~i3 the surface receiving the secondary beam, respectively in the case of a relatively small contact angle and a relatively high contact angle.
Figure 3 illustrates one embodiment of a device 5 comprising the improvements according to the invention.
Figure 4 is a variant of the embodiment of figure 3.
Figure 5 shows the problems arising from the use of a device according to the above French patent and figures 3 and 4 of the present application when the substrate is 10 made from a diffusing material.
Fi~ure 6 shows schematically how this disadvantage may be avoided using an accessory characteristic of the inventlon.
Figure 7, finally, illustrates the application of 15 the characteristic of figure 6 to a device of the invention, figure 7 being a variant of figure 3.
According to the invention and more particularly according to that one of its modes of application, as well as those of the embodiments of its different parts to 20 which it seems preference should be given, wishing for example to improve the methods and devices for determining the contact angle of a drop of liquid placed on a substrate, the following or similar is the procedure to follow.
A first embodiment of a device according to the invention is illustrated in figure 3.
In figure 3, we find again a laser 1 emittlng a beam 2 of horizontal and parallel rays which is ~idened, by an afocal optical system 3, into a more ex~ensive beam 4 hut 30 also formed of horizontal and parallel rays.
A prism 5a, with a reflecting surface 5b slanted by 45 with respect to the vertical, reflects the horizontal beam 4 into a primary ~eam 6 of parallel light, vertical in direction, which illuminates a zone 7 including the 35 interface between the periphery 8 of drop 9 and the horizontal ~urface 10 of substrate 11 carried movably by a 2a-~ 3~
support or sample holder 12.
According to a first characteristic of the invention, the rays 14 of the secondary beam from the interface between drop 9 and substrate 11, which form an angle equal to 2~' with the vertical, namely with rays 6, reach a receiving element 13 made from a reflection diffusing material with a reflecting face 13b. In particular, element 13a may be formed by an aluminium sheet or foil painted white on its face 13b.
Element 13a advantageously ha~ a truncated cone shape, the angle at the apex of the cone corresponding to the angular field of camera C.
With this reflectin~ surface 13b, the rays 14 of the secondary beam are reflected as rays 16. The conical 15 surface 13a is pierced with an orifice 13c for the passage of beam 4.
According to a second characteristic of the invention, a mirror 17 is provided forming a reflecting surface for rays 16 which are reflected as rays 18, a 20 great part of which reach camera C, particularly when the angle at the apex of the cone formed by element 13a corresponds to the field of the camera, when the periphery of the small base of the truncated cone surrounds camera C
and when the periphery of the large base thereof surrounds 25 the reflecting surface formed by mirror 17.
It can be seen that, because of the structure of the devlce of figure 13 comprising the reflection diffusing surface 13b of the conical element 13a, on the one hand, and mirror 17 on the other, camera C receives a large part 30 of the secondary beam of rays 14 after two reflections.
So that the rays 4 and 1~ may pass without difficulty, the reflecting prism 5a is carried by a tripod 1~ .
Instead of the assembly farmed by laser 1, the 35 afocal optical Rystem 3 and the reflecting prlsm Sa of figure 3, in a variant illustrated in figure 4, a laser rA ~ ~
diode la may be simply provided (with collimation means not shown) of a small diameter, fixed directly to the tripod 10 formed by three metal rods. In this case, the diffusing conical element 13a does not need to be pierced.
Apart from these modifications, the embodiment of figure 4 is identical to that of figure 3 and the same reference numbers have been used, from reference 6, in figure 4 and in figure 3.
In the embodiment of figure 4, as in that of figure 10 3, camera C receives, as rays 18, a large part of the rays 14 ~f the secondary beam after reflection from the reflecting surface 13b of element 13a and from mirror 17.
Another problem which arises in the use of the method and device according to the French patent 2 574 180 15 mentioned above comes from the diffusion which occurs on the upper horizontal surface 10 of sample 11 when the latter is very diffusing, the extent of the illumination transition presented by the secondary beam in correspondence with the periphery of the drop being then 20 very difficult to observe.
This phenomenon is illustrated in figure 5 in which has been ~hown the primary beam 6 of parallel and vertical rays which reach zone 7 including the periphery 8 of drop 9 and the flat upper horizontal surface 10 of substrate 11. In this figure, a ray 14 of the secondary beam has also been shown.
The phenomenon of diffusion at the surface 10 of substrate 11 ls illustrated by parasite rays 20a and 20b resulting from the reflection of rays 6 of the primary 30 beam from surface 10, not only rays 6 striking this surface 10 directly but al~o rays 6 passing through drop 9, whence respectively the parasite rays 20a and 20b.
According to a complementary characteristic of the invention, thls drawback which occurs when the substrate is very diffusing is overcome by illuminating the periphery 8 of drop 9 by an annular beam, which limits the parasite diffusion.
This is illustrated in figure 6 in which the annular primary beam is illustrated by the endmost rays ~a which arrive at the level of periphery 8 of drop 9 placed on 5 surface 10 of substrate 11. We find again a ray 14 of the secondary beam.
On the other hand, diffused rays of type 20a and 20b of figure 5 have not been shown since they are practically inexistent in the case of figure 6 when an annular primary 10 beam 6a is used.
In figure 7, one embodiment of the invention has been illustrated comprising not only the improvements of figure 3, but also the arrangement of figure 6.
In this embodiment, a laser l emits a beam 2 of 15 horizontal and parallel rays of coherent light, as in the embodiments of figures 1, 2 and 3.
On the other hand, the device of figure 7 does not have an afocal optical system (of the type bearing the reference 3 in figures 1, 2 and 3), b~t a thick plate 21 20 with parallel faces which is rotated (by means not shown) about its axis of rotation 22 while being slanted with respect to this axis. During rotation about axis 22 plate 21 produces, from beam 2, an annular beam 4a (in f~gure 7 the rays existing effectively at a given moment have been 25 shown with continuous lines and with broken lines the rays generated at another time during rotation of plate 3a).
The mean ray of the annular beam 4a is given by the formula R . e.cos r.(n-1)/n 30 r ~eing the angle of inclination of the plate, e the thickness there~f and n the index of the glass fo~m~n~ the plate which may for example be equal to 1.5. By modifying the inclination of plate 21 with respect to its axis of rotation 22, it is therefore possible to ad~ust R so as to 35 adapt it to the size of the liquid drop 9.
The annular beam 4a which has a horizontal axis, 3 ~ ~ ~
after passing through the opening 13c formed in the conical element 13a, is reflected by the surface 5b of a prism 5a, slanted by 45 with respect to the vertical, so as to form a primary annular beam 6a with vertical axis which strikes the contact zone of drop 9 and substrate 11, figure 16 in fact illustrating on a larger scale the portion of figure 7 in which the rays 6a arrive at the per~phery of drop 9.
As in the embodiment of figure 3, rays 6a are reflected as rays 14 then sent back by the reflecting surface 13b as rays 16, and finally by mirror 17 as rays 18 which are collected by camera C.
It is clear that with the embodiment of figure 7, a universal device is obtained for determining the contact angle of a drop of liquid placed on a horizontal substrate, which is solid or liquid, because it gives satisfactory results, even for a high contact angle close to 45, and even with a diffusing substrate, because camera C receives a large part of the rays such as 18 from the assembly of useful rays 14 of the secondary beam, even for a high contact angle, but receives practically no parasite rays (of type 20a, 20b of figure 5) which might be produced by diffusion when the ~ubstrate is very diffusing.
As is evident, the invention ls in no wise limited to the modes of application and embodiments which have been more especially envisaged; it embraces, on the contrary, all variants thereof.
Improvements to methods and devices for determin~n~ the contact angle of a drop of liquid placed on a substrate.
The present invention relates to the measurement of 5 the contact angle of a drop of liquid placed on a horizontally disposed solid or liquid substrate .
From the value of the contact angle between a drop of liquid and the horizontal surface of a substrate which carries the drop certain properties of the substrate can lO be derived, particularly its wettability and its surface condition, properties which are useful in fundamental or applied research.
The French patent 2 574 180 of the Centre National de la Recherche Scientifique, which recalls the main 15 applications of contact angle measurement, describes a method and device for determining the contact angle of a drop of liquid placed on a horizontal solid or liquid substrate, in which a primary beam of parallel light is directed 20 perpendicularly to the substrate for illuminating a zone of the assembly formed by the drop of liquid and the horizontal substrate (which zone includes the interface between the periphery of the drop and the substrate) while producing a secondary beam by interaction with the drop 25 and the ~ubstrate, and the extent of the illumination transition presented by the secondary beam in correspondence with the periphery of the drop is measured on a receiving surface intercepting this secondary beam.
However, the method and device of the above patent, which generally yives satisfactory results in the case of v~sual observation of the receiving surface, which is then a frosted surface, do not allow precise measurements to be made for all the drop-substrate pairs in the case of using a camera for displaying the illumination transition, in particular when the contact angle between the drop and the surface of the substrate is relatively high, for example close to 45~, and/or when the substrate is very diffusing.
In fact, although $n the case, illustrated in figure 1, of a low contact angle, it i~ possible with a device of 5 the type described in the above patent 2 574 180, to replace visual examination by a photographic image taken by a camera C, it is no longer the same in the case, illustrated ~n figure 2, of a contact angle close to 45, for the following reason.
Figures 1 and 2 reproduce substantially figure 8 of the above patent, but simplifying it.
In these figures l and 2, there have been designated:
by 1 a laser emitting a beam 2 of horizontal and 15 parallel rays, by 3 an afocal optical system widening beam 2 into a more extensive beam 4, but also formed of horizontal and parallel rays, this afocal optical system being shown solely in figure 1 which illustrates a plano-concave lens 20 3a and a plano-convex lens 3b, by 5 a reflecting mirror, slanted by 45 with respect to the vertical, which produces the primary beam 6 of parallel light, vertical in direction, which illuminates on the assembly to be observed a zone 7 which includes the interface between the periphery 8 of drop 9 and the horlzontal surface 10 of substrate 11, which is for example solld, carried movably by a sample-holder 12, and by 13 a receiving surface interceptin~ the secondary 30 beam 14 resulting from the interaction of the pr~mary beam wlth the drop 9 and substrate 11.
In figures l and 2 have been shown, specially in the primary ~ and secondary 14 beams, the rays directed to and coming from the perlphery 8 of drop 9, namely from the 35 drop-substrate interface, the angle of these rays 14 of the secondary beam with respect to the vertical, so with 2~ J_ the corresponding rays 6 of the primary beam, being twice (2~) the drop-substrate contact angle referenced~.
Although a camera C may, in the case of figure 1 where the contact angle ~ is relatively small (for example 5 not exceeding 10 to 20), receive a large part of the rays such as 15 from the receiving surface 13 and corresponding to the rays 14 of the secondary beam from the periphery 8 of drop 9, it ls no longer the same $n the case of figure 2, where the contact angle ~' is relatively close to 45, 10 for example about 40 and so the angle 2~' about 80, for then camera C recelves practically no rays 15' from the receiving surface 13 and corresponding to the rays of the secondary beam 14 from the periphery 8 of drop 9.
Consequently, although the illumination transition 15 corresponding to the periphery 8 of drop 9 can be readily detected by camera C in figure 1 which receives numerous rays from surface 13, on the other hand observation of this transition is difficult using camera C of figure 2 which receives very few rays from this surface 13.
In order to observe the illumination transition corresponding to the periphery of the drop under excellent conditions, using a camera, even for a relatively high contact angle which may reach about 45, in accordance wlth ~he invention, the surface receiving the secondary 25 beam i8 formed by a reflection dlffusing surface and a reflecting surface is disposed for reflecting the light from this receiving surface towards the camera, so as to concen~rate on the ob~ective of the latter at least the ma~ority of rays form~ng the secondary beam and 30 corresponding par~icularly to the periphery of the drop.
The object of the lnvention is first of all to provide a method for determining the contact angle of a drop of li~uid placed on a substrate, for any contact angle less than 45~, which consists in directing 35 perpend~cularly to the substrate a primary beam of parallel light for illuminating a zone which contains the 2 a ~
interface between the periphery of the drop and the substrate, determlning the illumination transition zone presented by a secondary beam resulting from the interaction of the primary beam with the drop and the substrate, on at least one receiving surface lntercepting this beam, and is characterized in that said receiving surface is a reflection diffusing surface, in that a reflecting surface is provided disposed inside said diffusing receiving surface for reflecting the light rays from said diffusing receiving surface, and in that the rays reflected by said reflecting surface are collected by a camera.
The invention also has as object a device for implementing the above method, comprising a support for holdin~ a substrate horizontal on which is placed a drop of liquid, a light source associated with optical means for forming from the light source a primary beam of parallel light directed perpendicularly to the substrate, at least one receiving surface surrounding the substrate for intercepting the returning secondary beam producsd by interaction of the primary beam with the drop and the substrate, and is characterized ln that said receiving surface is formed by a reflection diffusing surface, in that a reflecting surface is disposed inside said diffusing receiving surface for reflecting the beam of rays reflected by said diffusing receiving surface and in that lt comprises a camera disposed for collecting the rays reflected by said reflecting surface.
The invention will in any case be well understood from the following complement of descript~on and the accompanying drawings, which complement and drawings are of course given by way of example.
Figures 1 and 2, already described above, illustrate schematically the problems arising from the use of a 3~ dsvice accordin~ to figure ~ of the above mentioned French patent when it is desired to use a camera for observing 2~t3~i3 the surface receiving the secondary beam, respectively in the case of a relatively small contact angle and a relatively high contact angle.
Figure 3 illustrates one embodiment of a device 5 comprising the improvements according to the invention.
Figure 4 is a variant of the embodiment of figure 3.
Figure 5 shows the problems arising from the use of a device according to the above French patent and figures 3 and 4 of the present application when the substrate is 10 made from a diffusing material.
Fi~ure 6 shows schematically how this disadvantage may be avoided using an accessory characteristic of the inventlon.
Figure 7, finally, illustrates the application of 15 the characteristic of figure 6 to a device of the invention, figure 7 being a variant of figure 3.
According to the invention and more particularly according to that one of its modes of application, as well as those of the embodiments of its different parts to 20 which it seems preference should be given, wishing for example to improve the methods and devices for determining the contact angle of a drop of liquid placed on a substrate, the following or similar is the procedure to follow.
A first embodiment of a device according to the invention is illustrated in figure 3.
In figure 3, we find again a laser 1 emittlng a beam 2 of horizontal and parallel rays which is ~idened, by an afocal optical system 3, into a more ex~ensive beam 4 hut 30 also formed of horizontal and parallel rays.
A prism 5a, with a reflecting surface 5b slanted by 45 with respect to the vertical, reflects the horizontal beam 4 into a primary ~eam 6 of parallel light, vertical in direction, which illuminates a zone 7 including the 35 interface between the periphery 8 of drop 9 and the horizontal ~urface 10 of substrate 11 carried movably by a 2a-~ 3~
support or sample holder 12.
According to a first characteristic of the invention, the rays 14 of the secondary beam from the interface between drop 9 and substrate 11, which form an angle equal to 2~' with the vertical, namely with rays 6, reach a receiving element 13 made from a reflection diffusing material with a reflecting face 13b. In particular, element 13a may be formed by an aluminium sheet or foil painted white on its face 13b.
Element 13a advantageously ha~ a truncated cone shape, the angle at the apex of the cone corresponding to the angular field of camera C.
With this reflectin~ surface 13b, the rays 14 of the secondary beam are reflected as rays 16. The conical 15 surface 13a is pierced with an orifice 13c for the passage of beam 4.
According to a second characteristic of the invention, a mirror 17 is provided forming a reflecting surface for rays 16 which are reflected as rays 18, a 20 great part of which reach camera C, particularly when the angle at the apex of the cone formed by element 13a corresponds to the field of the camera, when the periphery of the small base of the truncated cone surrounds camera C
and when the periphery of the large base thereof surrounds 25 the reflecting surface formed by mirror 17.
It can be seen that, because of the structure of the devlce of figure 13 comprising the reflection diffusing surface 13b of the conical element 13a, on the one hand, and mirror 17 on the other, camera C receives a large part 30 of the secondary beam of rays 14 after two reflections.
So that the rays 4 and 1~ may pass without difficulty, the reflecting prism 5a is carried by a tripod 1~ .
Instead of the assembly farmed by laser 1, the 35 afocal optical Rystem 3 and the reflecting prlsm Sa of figure 3, in a variant illustrated in figure 4, a laser rA ~ ~
diode la may be simply provided (with collimation means not shown) of a small diameter, fixed directly to the tripod 10 formed by three metal rods. In this case, the diffusing conical element 13a does not need to be pierced.
Apart from these modifications, the embodiment of figure 4 is identical to that of figure 3 and the same reference numbers have been used, from reference 6, in figure 4 and in figure 3.
In the embodiment of figure 4, as in that of figure 10 3, camera C receives, as rays 18, a large part of the rays 14 ~f the secondary beam after reflection from the reflecting surface 13b of element 13a and from mirror 17.
Another problem which arises in the use of the method and device according to the French patent 2 574 180 15 mentioned above comes from the diffusion which occurs on the upper horizontal surface 10 of sample 11 when the latter is very diffusing, the extent of the illumination transition presented by the secondary beam in correspondence with the periphery of the drop being then 20 very difficult to observe.
This phenomenon is illustrated in figure 5 in which has been ~hown the primary beam 6 of parallel and vertical rays which reach zone 7 including the periphery 8 of drop 9 and the flat upper horizontal surface 10 of substrate 11. In this figure, a ray 14 of the secondary beam has also been shown.
The phenomenon of diffusion at the surface 10 of substrate 11 ls illustrated by parasite rays 20a and 20b resulting from the reflection of rays 6 of the primary 30 beam from surface 10, not only rays 6 striking this surface 10 directly but al~o rays 6 passing through drop 9, whence respectively the parasite rays 20a and 20b.
According to a complementary characteristic of the invention, thls drawback which occurs when the substrate is very diffusing is overcome by illuminating the periphery 8 of drop 9 by an annular beam, which limits the parasite diffusion.
This is illustrated in figure 6 in which the annular primary beam is illustrated by the endmost rays ~a which arrive at the level of periphery 8 of drop 9 placed on 5 surface 10 of substrate 11. We find again a ray 14 of the secondary beam.
On the other hand, diffused rays of type 20a and 20b of figure 5 have not been shown since they are practically inexistent in the case of figure 6 when an annular primary 10 beam 6a is used.
In figure 7, one embodiment of the invention has been illustrated comprising not only the improvements of figure 3, but also the arrangement of figure 6.
In this embodiment, a laser l emits a beam 2 of 15 horizontal and parallel rays of coherent light, as in the embodiments of figures 1, 2 and 3.
On the other hand, the device of figure 7 does not have an afocal optical system (of the type bearing the reference 3 in figures 1, 2 and 3), b~t a thick plate 21 20 with parallel faces which is rotated (by means not shown) about its axis of rotation 22 while being slanted with respect to this axis. During rotation about axis 22 plate 21 produces, from beam 2, an annular beam 4a (in f~gure 7 the rays existing effectively at a given moment have been 25 shown with continuous lines and with broken lines the rays generated at another time during rotation of plate 3a).
The mean ray of the annular beam 4a is given by the formula R . e.cos r.(n-1)/n 30 r ~eing the angle of inclination of the plate, e the thickness there~f and n the index of the glass fo~m~n~ the plate which may for example be equal to 1.5. By modifying the inclination of plate 21 with respect to its axis of rotation 22, it is therefore possible to ad~ust R so as to 35 adapt it to the size of the liquid drop 9.
The annular beam 4a which has a horizontal axis, 3 ~ ~ ~
after passing through the opening 13c formed in the conical element 13a, is reflected by the surface 5b of a prism 5a, slanted by 45 with respect to the vertical, so as to form a primary annular beam 6a with vertical axis which strikes the contact zone of drop 9 and substrate 11, figure 16 in fact illustrating on a larger scale the portion of figure 7 in which the rays 6a arrive at the per~phery of drop 9.
As in the embodiment of figure 3, rays 6a are reflected as rays 14 then sent back by the reflecting surface 13b as rays 16, and finally by mirror 17 as rays 18 which are collected by camera C.
It is clear that with the embodiment of figure 7, a universal device is obtained for determining the contact angle of a drop of liquid placed on a horizontal substrate, which is solid or liquid, because it gives satisfactory results, even for a high contact angle close to 45, and even with a diffusing substrate, because camera C receives a large part of the rays such as 18 from the assembly of useful rays 14 of the secondary beam, even for a high contact angle, but receives practically no parasite rays (of type 20a, 20b of figure 5) which might be produced by diffusion when the ~ubstrate is very diffusing.
As is evident, the invention ls in no wise limited to the modes of application and embodiments which have been more especially envisaged; it embraces, on the contrary, all variants thereof.
Claims (7)
1. Method for determining the contact angle of a drop of liquid placed on a substrate, for any contact angle less than 45°, which consists in directing per-pendicularly to the substrate a primary beam of paralell light for illuminating a zone which contains the inter-face between the periphery of the drop and the substra-te, determining the illumination transition zone presen-ted by a secondary beam resulting from the interaction of the primary beam with the drop and the substrate, on at least one receiving surface intercepting this beam, and is characterized in that said receiving surface is a reflection diffusing surface, in that a reflecting sur-face is provided disposed inside said diffusing recei-ving surface for reflecting the light rays from said diffusing receiving surface, and in that the rays re-flected by said reflecting surface are collected by a camera.
2. Method according to claim 1, characterized in that the primary beam is annular.
3. Device for implementing a method for determi-ning the contact angle of a drop of liquid placed on a substrate, for any contact angle less than 45°, said method consisting in directing perpendicularly to the substrate a primary beam of parallel light for illumina-ting a zone which contains the interface between the periphery of the drop and the substrate, determining the illumination transition zone presented by a secondary beam resulting from the interaction of the primary beam with the drop and the substrate, on at least one recei-ving surface intercepting this beam, said device compri-sing a support (12) adapted for holding a substrate (11) horizontal on which is placed a drop of liquid (9), a light source (1, 1a) associated with optical means (3, 5a, 5b; 1, 21, 5a, 5b) for forming from the light source a primary beam (6; 6a) of parallel light directed perpendicularly to the substrate, at least one receiving surface (13a, 13b) surrounding the substrate for inter-cepting the returning secondary beam (14) produced by interaction of the primary beam with the drop and the substrate, and is characterized in that said receiving surface (13a, 13b) is formed by a reflection diffusing surface, in that a reflecting surface (17) is disposed inside said diffusing receiving surface for reflecting the beam of rays (16) reflected by said diffusing re-ceiving surface and in that it comprises a camera (C) disposed for collecting the rays (18) reflected by said reflecting surface.
4. Device according to claim 3, characterized in that the diffusing receiving surface (13a, 13b) has the form of a hollow truncated cone whose small base peri-phery surrounds the camera (C) and whose large base pe-riphery surrounds said reflecting surface (17), the angle at the apex of the cone corresponding to the angu-lar field of the camera.
5. Device according to claim 3 for implementing the method according to claim 2, characterized in that it comprises means (21) for transforming the light beam emitted by the light source (1) into an annular beam which will become the primary beam (6a) also annular.
6. Device according to claim 5, characterized in that said means for transforming said light beam emitted by the light source into an annular beam comprise a pla-te with parallel faces (21) whose inclination with res-pect to an axis of rotation (22) may be modified, this axis being parallel to the direction of the rays of the light beam (2) which the plate with parallel faces receives from the light source (1), and means for rotating the plate with parallel faces about it axis of rotation.
7. Device according to claim 3, characterized in that the diffusing receiving surface (13a, 13b) is made from aluminium painted white.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR8904530 | 1989-04-06 | ||
FR8904530A FR2645645B1 (en) | 1989-04-06 | 1989-04-06 | IMPROVEMENTS IN METHODS AND DEVICES FOR DETERMINING THE ANGLE OF CONTACT OF A DROP OF LIQUID PLACED ON A SUBSTRATE |
Publications (1)
Publication Number | Publication Date |
---|---|
CA2013691A1 true CA2013691A1 (en) | 1990-10-06 |
Family
ID=9380448
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002013691A Abandoned CA2013691A1 (en) | 1989-04-06 | 1990-04-03 | Methods and devices for detemining the contact angle of a drop of liquid placed on a substrate |
Country Status (6)
Country | Link |
---|---|
US (1) | US5115677A (en) |
EP (1) | EP0391801B1 (en) |
JP (1) | JPH02287236A (en) |
CA (1) | CA2013691A1 (en) |
DE (1) | DE69000920T2 (en) |
FR (1) | FR2645645B1 (en) |
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JPS5776439A (en) * | 1980-10-30 | 1982-05-13 | Dainippon Printing Co Ltd | Method for measurement of contact angle |
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-
1989
- 1989-04-06 FR FR8904530A patent/FR2645645B1/en not_active Expired - Fee Related
-
1990
- 1990-04-03 CA CA002013691A patent/CA2013691A1/en not_active Abandoned
- 1990-04-04 EP EP90400927A patent/EP0391801B1/en not_active Expired - Lifetime
- 1990-04-04 DE DE9090400927T patent/DE69000920T2/en not_active Expired - Fee Related
- 1990-04-05 US US07/504,799 patent/US5115677A/en not_active Expired - Fee Related
- 1990-04-06 JP JP2090476A patent/JPH02287236A/en active Pending
Also Published As
Publication number | Publication date |
---|---|
EP0391801A1 (en) | 1990-10-10 |
FR2645645A1 (en) | 1990-10-12 |
EP0391801B1 (en) | 1993-02-17 |
US5115677A (en) | 1992-05-26 |
FR2645645B1 (en) | 1991-07-12 |
DE69000920T2 (en) | 1993-06-03 |
JPH02287236A (en) | 1990-11-27 |
DE69000920D1 (en) | 1993-03-25 |
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