WO2015058927A1 - Procédé optique et dispositif optique pour déterminer une propriété d'un objet partiellement transparent sur une surface de support partiellement réfléchissante, et support d'enregistrement lisible par ordinateur - Google Patents

Procédé optique et dispositif optique pour déterminer une propriété d'un objet partiellement transparent sur une surface de support partiellement réfléchissante, et support d'enregistrement lisible par ordinateur Download PDF

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Publication number
WO2015058927A1
WO2015058927A1 PCT/EP2014/070743 EP2014070743W WO2015058927A1 WO 2015058927 A1 WO2015058927 A1 WO 2015058927A1 EP 2014070743 W EP2014070743 W EP 2014070743W WO 2015058927 A1 WO2015058927 A1 WO 2015058927A1
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WO
WIPO (PCT)
Prior art keywords
light
support surface
detected
property
reflected
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Application number
PCT/EP2014/070743
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German (de)
English (en)
Inventor
Manuel Lorenz
Original Assignee
Technische Universität München
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Publication of WO2015058927A1 publication Critical patent/WO2015058927A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/255—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures for measuring radius of curvature
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • 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

Definitions

  • the present invention relates to a method and a device for determining a property of an object such as a drop of liquid, in particular a geometric property, such as a contact angle between the object and a support surface on which the object is arranged.
  • Determining the wettability of surfaces with liquids plays an important role in various technical areas, such as printing technology, materials science or condensation processes in energy technology.
  • the wettability can be determined via the forming contact angle between a drop of liquid and a horizontal level bearing surface.
  • EP 0 919 801 A1 discloses a contact angle measuring device for measuring the contact angle formed by a drop to a surface of a sample body.
  • the measuring device has a camera, which images the transition region between the drop and the surface of the sample body in a side view.
  • Disadvantage of such methods is that they are difficult to automate and allow only the detection of individual drops.
  • the optical detection of the baseline ie the laterally projected support surface, associated with a relatively large inaccuracy.
  • EP 2 093 557 A2 discloses a method for determining the contact angle between a sample surface, a gaseous environment and a drop arranged on the sample surface.
  • an object is imaged based on the reflection properties of the surface of the drop, the position of the object being to the optical axis of an optical measuring system and the position of the object to the sample surface are known.
  • the symmetry axis of the drop is located in or near the optical axis.
  • only one drop can be measured simultaneously.
  • the radius of curvature or the contact angle can be determined with the method, but not further geometric information, such as the drop volume. Rather, the drop volume must be known by other methods, for example by an accurate dosage during the application, in order to be able to determine the contact angle at all.
  • the invention provides a method in which at least one object, such as a drop, is arranged on an at least partially reflecting support surface and light is irradiated onto the support surface and the at least one object arranged thereon. A first light component of the incident light is reflected on a curved surface of the at least one object and subsequently detected.
  • a second light portion of the incident light is refracted when penetrating the object at the curved surface, is then reflected at an interface between the object and the support surface, refracted upon exiting the object at the curved surface, and is subsequently detected. At least one property of the object is determined based on the detected first light portion and the detected second light portion.
  • the method thus makes it possible to determine a property of the object, such as, for example, a contact angle between the object and the support surface or of the object volume in a single measurement process.
  • the courses of two light components are detected: a first light component is reflected directly on the curved surface of the object and detected, for example, with an optical sensor.
  • a second portion of light initially enters the object, wherein the second portion of light is refracted upon entering the object due to the different refractive indices of the object and the surrounding medium when entering the object.
  • the second portion of light then strikes the interface between the object and the support surface, where it is reflected back into the object.
  • the second light component again passes through the curved surface of the object, where it is refracted again.
  • the second light component is then detected, for example, with the same sensor.
  • the image picked up by the optical sensor includes a bright surface having a position and a shape.
  • the term form does not only include qualitative typing such as e.g. circular or angular, but also quantitative parameters, such as a radius of a circular in the image light component.
  • the at least one property of the object is determined. For example, the positions at which the first light share and the second portion of light on the sensor surface of the camera meet determined to determine the radius of curvature or the contact angle of the object. In particular, the distance of the positions at which the first light component and the second light component strike the sensor surface of the camera can be determined for this purpose.
  • the shapes of the lights in the captured image can be detected. In particular, with light components which at least partially follow a circular line in the recorded image, the radii of the light components in the recorded image can be detected.
  • the light can be radiated from above and also the observation from above, the objects are not disturbed in their training and their behavior by the measurement. For example, objects can be examined in ongoing condensation experiments without the tests being disturbed by the measuring method. Moreover, the method according to the invention also provides reliable and accurate results even at contact angles between object and contact surface of 90 ° and more.
  • the object may be liquid, solid or gaseous or contain two or more liquid, solid and / or gaseous components.
  • the object may be, for example, a drop, in particular a drop of liquid.
  • the object can be formed from a solid, for example from a solidified liquid.
  • the object may be gaseous or comprise a gas.
  • the object may be, for example, a bubble in a surrounding solid or a surrounding liquid.
  • the method can also be used for objects that consists of a mixture of several liquids, gases and / or solids. It is only necessary in this context for the screened surface of the object to define an interface between media having different refractive indices, such as between the object and the surrounding media surrounding the object.
  • the object at the curved surface may be adjacent to a surrounding medium having a different index of refraction than the object or a portion of the object adjacent to the curved surface.
  • the surrounding medium may be a gas, such as air.
  • the surrounding medium may be a liquid or a solid.
  • the surrounding medium may have the same or a different state of aggregation than the object.
  • the light can be radiated in a fixed angle relative to the support surface. In this way, all parts of the light are irradiated at an equal angle relative to the support surface.
  • the support surface and the at least one object may alternatively or additionally be arranged such that the first light component after the reflection on the at least one object runs approximately parallel and that the second light component after the refraction when leaving the object runs approximately parallel.
  • the at least one object is transparent at least at one wavelength or in at least one wavelength range of the incident light.
  • the second light portion of the irradiated light can thus at least partially penetrate into the object.
  • the irradiated light may include, for example, light in the visible wavelength range.
  • light having a wavelength or a wavelength range tuned to the at least one object may be used.
  • a wide range of object properties can be determined with the method according to the invention.
  • any property which has an influence on the reflection at the curved surface of the object, the refraction on the curved surface and / or the reflection at the interface between object and bearing surface can be determined.
  • a refractive index of the object can be determined.
  • the object geometry is unknown.
  • the inventive method can be used to determine the object geometry.
  • the at least one property of the object is a geometric property of the object, in particular a radius of curvature, a contact angle to the support surface or an object volume.
  • the ob- jektvolumen be determined, for example, to evaluate a metering device for the objects, such as drops, and possibly to adjust.
  • the light is radiated by a light source, which extends in an annular manner about an axis or has a plurality of light-emitting regions arranged around an axis, in particular equidistant from the axis.
  • the annular light source may in particular be defined by a circular line which runs concentrically around the axis.
  • the axis may in some cases be an axis of symmetry of the light source. Alternatively or additionally, the axis can run perpendicular to a plane defined by the light source and / or run through a geometric center of the light source.
  • the axis is aligned perpendicular to the support surface.
  • the shapes of the detected light components in the recorded image essentially have a similar shape to that of the light source.
  • the distribution of the first and second light components in the case of a symmetrical object shape is likewise approximately annular.
  • the distribution of the light components corresponds to the shape of the light source even more, if in addition the axis of the light source is aligned perpendicular to the support surface.
  • the radii of the detected first and second light components, for example, in an image recorded by an optical sensor can be easily determined in order to determine therefrom the at least one property of the object, as will be described in detail below. In this way, the automated determination of the object property, in particular when examining a large number of objects, is simplified.
  • the first and second light components are detected in a region around the optical axis of the light source.
  • the first and second light components can be detected with an optical sensor which detects light coming from the contact surface along the axis of the light source.
  • the optical sensor can be aligned along the axis of the light source.
  • the axis of the light source can run, for example, through a sensor surface of the optical sensor.
  • it can be provided between the support surface and the optical sensor, an optics along the axis of the support surface coming light directed to a sensor surface of the optical sensor.
  • At least the first and the second light component are irradiated in an approximately constant angle within an observation area of the support surface onto the support surface with the at least one object arranged thereon.
  • An angle can be considered, for example, as approximately constant when the angular deviation of the beam paths of the light components is less than 4 °.
  • the light portions reflected within an observation area of the support surface are detected, wherein the observation area has a diameter, and wherein a distance between the light source and the support surface is at least five times, in particular at least ten times larger than the diameter of the observation area.
  • a distance between an optical sensor which detects the first and the second light component, or an objective arranged in the optical path in front of the optical sensor and the support surface is at least five times, in particular at least ten times, larger than the diameter of the observation region.
  • the irradiated light components approximately within the observation area at an equal angle to the support surface so that, for example, a plurality of objects can be examined simultaneously under approximately the same angular conditions.
  • the observation area describes the entire bearing surface or a subarea thereof, including the at least one object arranged thereon.
  • the diameter of the observation area may be, for example, 5 cm when raindrops are to be examined on a disk, wherein the distance between the light source and the support surface and the distance between the lens and support surface may be about 1 m.
  • the light is radiated at an angle between 5 ° and 60 °, in particular between 10 ° and 30 ° and preferably between 15 ° and 25 ° relative to the axis.
  • angles of incidence it is achieved in the case of many object materials that a first light component is reflected at the curved surface of the object and a second light component is refracted.
  • too low or too steep angles of incidence would have the disadvantage that, depending on the object geometry, the first or second light component can no longer be detected since the reflection and refraction conditions of a beam path from the light source to the sensor are no longer met.
  • a shutter is provided in the beam path between the support surface and the optical sensor.
  • stray light and other light which does not correspond to the light components to be detected, can be prevented from reaching the optical sensor. It is preferred that the rays strike the optical sensor or the lens almost perpendicularly and / or with almost the same angle.
  • a diaphragm is used which determines which sensor angles of incidence can still be detected.
  • Light source causes a wide-open aperture the image of the light source as two relatively wide circular lines.
  • a closed aperture there are two sharp thin circle lines.
  • a closed diaphragm is preferred because in this case there are fewer possible beam paths from the light source to the optical sensor and a higher measurement accuracy can be achieved. Irrespective of the diaphragm, the choice of the correct distance from the light source or optical sensor or objective from the support surface or the choice of a smaller observation region makes it possible for the angular proportions of the light components to be similar for the entire observation region.
  • a third light component of the irradiated light is reflected outside the at least one object on the support surface, reflected on the curved surface of the object and subsequently detected, wherein the property of the object is further determined based on the detected third light component.
  • a further information about the properties such as a geometric shape of the object is determined.
  • various calculation methods can be used, each based on one or two of these three lights, and the results can then be compared.
  • an average of the values calculated for the geometric property by means of the different calculation methods can be determined. In this way, the measurement accuracy for the geometric property is further improved.
  • the positions or shapes of the three lights can be captured and evaluated to more than one property 0743
  • the radius of curvature, object volume and contact angle can be determined simultaneously.
  • a plurality of objects are arranged on the support surface, wherein the first and second light portions reflected at the plurality of objects are detected simultaneously, and the at least one property for each of the plurality of objects based on the detected first and second objects second light components is determined.
  • This embodiment enables the rapid determination of one or more properties of a plurality of objects in a single measurement operation. In this way, for example, a statistical distribution of the property (s) can be efficiently determined, which would require a large number of successively performed measurement processes in conventional measuring methods for determining the contact angle.
  • This is particularly advantageous in embodiments in which the geometric property is determined at different points in time, as will be explained below.
  • the plurality of objects may for example comprise at least 5, in particular at least 100 and preferably at least 1000 objects.
  • the first and the second light component are each detected at at least two times, and the property of the object at the at least two times is determined based on the detected first light component and the detected second light component.
  • the temporal evolution of the object property can be determined.
  • the third light component can be detected at the same points in time as the first and the second light component. It can further be provided that, based on the object properties determined for the at least two times, a change of the at least one object, a type of the at least one object and / or an environmental condition is ascertained.
  • the first and the second light component are respectively detected periodically and the property of the object is determined at the times based on the periodically detected first light component and the periodically detected second light component.
  • the times may have a constant time interval, the for example less than five minutes, in particular less than one minute and preferably about 10 s.
  • the method is not limited to a specific time interval.
  • the light components can be recorded in very short time intervals and evaluated either in real time or with a time offset or only after completion of the measurement in order to determine the at least one property.
  • the method further comprises placing the at least one object on the support surface by spraying.
  • the at least one object can be arranged by condensation on the support surface.
  • the at least one object is arranged with a tool, such as a needle on the support surface.
  • the invention provides an apparatus.
  • the device comprises a receptacle which is set up to receive a support element with an at least partially reflective support surface on which at least one object is arranged or can be arranged, and a light source which is configured to directly or indirectly light it to illuminate an observation area of the support surface.
  • the apparatus further comprises an optical sensor arranged to take an image of the observation area, the image comprising a first portion of the incident light reflected at a curved surface of the at least one object and a second portion of the incident light which is refracted when penetrating the object at the curved surface, reflected at an interface between the object and the support surface, and refracted upon exiting the object at the curved surface.
  • the device comprises an evaluation circuit coupled to the optical sensor, which is designed to detect a position or shape of the first light component and a position or shape of the second light component in the recorded image, and at least one property of the object based on the detected one Determine positions or shapes.
  • the optical sensor may comprise, for example, an image sensor, in particular a camera, for example a CCD camera or a CMOS camera.
  • the optical sensor can record the image, for example, after the interaction of the light components coming from the observation area with an optical system, for example a lens.
  • the observation area corresponds to the subarea of the bearing surface, which is shown in the image taken by the optical sensor.
  • the evaluation circuit includes an output for outputting the at least one characteristic.
  • the Von-direction may further comprise a memory coupled to the evaluation circuit to store therein the at least one certain property.
  • the device may comprise a display device coupled to the evaluation circuit in order to indicate the specific property.
  • the at least one property of the object is a geometric property of the object, in particular a radius of curvature, a contact angle to the support surface or an object volume.
  • the light source extends in an annular manner about an axis or has a plurality of light-emitting regions arranged around an axis, in particular equidistant from the axis.
  • the light emitting areas can be spatially separated from each other. It is particularly preferred that the light source surrounds the optical sensor or a detection axis of the optical sensor.
  • the detection axis of the optical sensor can be parallel to the axis of the light source and in particular be identical to this.
  • the optical sensor is arranged such that it detects light components coming from the observation area along the axis of the light source.
  • the optical sensor can be arranged, for example, along the axis of the light source.
  • a sensor surface can intersect the axis and be arranged, for example, perpendicular to the axis.
  • an optical system is provided between the support surface and the optical sensor, which directs light components coming from the observation region along the axis of the light source to the optical sensor and / or images it, such as an objective.
  • the axis of the light source is oriented substantially perpendicular to the support surface.
  • a detection axis of the optical sensor which is possibly provided by an optical system, be aligned substantially perpendicular to the support surface.
  • An axis is substantially perpendicular to the support surface when it includes an area normal of the support surface an angle of less than 10 °, in particular less than 5 ° and preferably less than 1 °.
  • a lens is arranged in the beam path in front of the optical sensor.
  • the objective may, for example, be convex in order to achieve a strong magnification of the recorded image of the observation area.
  • the lens may be a long-distance lens that allows a large working distance to the object with a focal length in the range of several centimeters, for example 8 to 50 cm.
  • the magnifications are then in the range of 0.1 to 10 and can, for example, the adaptation of the observation area on the size of the camera chip, which is only a few square millimeters large serve.
  • Harsh Environment Conditions such as Harsh Environment Conditions.
  • a transparent screen such as a protective glass
  • the optical sensor, the support surface, the light source and the at least one object are further arranged such that the captured image moreover a third portion of the incident light reflected outside the at least one object on the support surface and on the curved surface of the object is reflected, captured.
  • the evaluation circuit is further configured to detect a position or shape of the third light portion in the captured image and to further determine the property of the object based on the detected position or shape of the third light portion.
  • a distance between the light source and the support surface is at least ten times larger than a diameter of the observation region and a distance between the optical sensor or a lens arranged in front of the optical path and the support surface is at least five times, in particular at least ten times larger than a diameter of the observation area.
  • the optical sensor is adapted to record images of the observation area at at least two successive time intervals
  • the evaluation circuit is further configured to detect the positions or shapes of at least the first and second light components in the at least two recorded images and the Property of the object at the at least two times based on the detected positions or shapes to determine.
  • the evaluation circuit may be configured to store the properties of the object or of the plurality of objects determined at the different time intervals in the memory.
  • the evaluation circuit can also be set up to determine a temporal change of the object, a type of the object and / or an environmental condition based on the object properties determined at the at least two points in time.
  • a plurality of objects are arranged on the support surface and the evaluation circuit is adapted to the positions or shapes of the first and second reflected on the plurality of objects
  • the device further comprises a support member received in the receptacle with an at least partially reflective support surface for at least one object.
  • the support surface may be formed, for example, hydrophobic or hydrophilic.
  • the support surface may have a recess for receiving the at least one object.
  • a computer-readable medium for use with a device.
  • the device comprises a receptacle which is adapted to provide a support element with an at least partially reflective support. surface, on which at least one object is arranged or can be arranged, and a light source which is configured to directly or indirectly irradiate light into an observation area of the support surface.
  • the apparatus further comprises an optical sensor arranged to capture an image of the observation area, the image comprising a first portion of the incident light reflected at a curved surface of the at least one object and a second portion of the incident light is refracted when penetrating the object at the curved surface, is reflected at an interface between the object and the support surface, and is refracted upon exiting the object at the curved surface.
  • the device may in particular be a device of the type described above.
  • the computer-readable medium has instructions stored thereon which, when executed by a processor, cause the processor to receive an image captured by the optical sensor and a position or shape of the first portion of light and a position or shape of the second portion of light capture the captured image, and determine at least one property of the object based on the detected positions or shapes.
  • the computer-readable medium may include, for example, a semiconductor memory such as a dynamic random access memory (DRAM), a static random access memory (SRAM), an EPROM, or an EEPROM.
  • the computer-readable medium may include a magnetic and / or optical storage medium such as a hard disk, a memory card, a CD-ROM, a DVD, a USB memory, or the like.
  • the stored instructions when executed by the processor, further cause the processor to evaluate the image captured by the optical sensor by the processor determining a position or shape of a third portion of light reflected from the light source in the observation area which is reflected outside the at least one object on the support surface and reflected by the surface of the object, detects the captured image and further determines the at least one property of the object based on the detected position or shape of the third light component.
  • the optical sensor of the device is configured to display images of the observation area on at least two successive points in time 0743
  • the stored instructions when executed by the processor, further cause the processor to detect the positions or shapes of at least the first and second light portions in the at least two captured images and the property of the object at the at least two time points based on the determined positions or shapes.
  • the stored instructions when executed by the processor, cause the processor to further determine, for each object of a plurality of objects disposed on the support surface within the viewing area, the positions or shapes of the first and second portions of light capture the captured image and determine, for each object of the plurality of objects, the at least one property based on the positions or shapes of the detected first and second lights.
  • FIG. 1 is a schematic representation of the device according to an embodiment in a cross-sectional view
  • FIG. 3 shows the relationship between the contact angle of an object and the ratio of the radii of the ring-shaped detected light components in a captured image according to one embodiment.
  • FIG. The marked end points of the curve indicate the detectable measuring range dependent on the angle of incidence of the light source.
  • FIG. 4 shows images on which the positions and shapes of the first, second and third detected light components are visible, and cross-sectional views of the droplet at different times, wherein the droplet is arranged on a polycarbonate surface
  • Fig. 5 shows the contact angle to the images of Fig. 4 as a function of time
  • FIG. 6 shows images on which the positions and shapes of the first, second and third detected light components are visible, as well as cross-sectional views of the droplet. at different times, the drop being arranged on a hydrophobic surface,
  • Fig. 7 shows the contact angle to the images of FIG. 6 as a function of time
  • FIG. 8 shows images in which the positions and shapes of the first, second and third detected light components are visible, and cross-sectional views of the droplet at different times, wherein the droplet is arranged on a hydrophilic surface
  • Fig. 9 shows the contact angle to the images of Fig. 8 as a function of time, with the
  • FIG. 10 shows images on which the positions and shapes of the first, second and third detected light components are visible, and cross-sectional views of the droplet at different times, wherein the droplet was arranged on a hydrophobic surface.
  • the drop in this experiment had a size in which the influence of gravity was pronounced.
  • FIG. 10 shows the contact angle to the images of FIG. 10 as a function of the time measured by the method according to an embodiment with consideration of the influence of gravity and the method known from the prior art, FIG.
  • Fig. 12 is a diagram on which the positions and shapes of the first and second at a
  • FIG. 13 shows a bar chart of the statistical distribution of the contact angle measured with a method according to an embodiment in a condensation test on a polycarbonate surface with subsequent defrosting and
  • Fig. 14 which is determined by the experienced according to an embodiment and normalized
  • the method according to the invention makes it possible to determine one or more properties, in particular geometric properties, of one or more objects. For example, the contact angle and / or the volume of a large number of objects be determined at the same time low metrological effort when using the method according to the invention.
  • Fig. 1 shows a schematic representation of the device according to the invention according to an embodiment in a cross-sectional view.
  • an objective 2 is installed vertically above one or more objects 6 which are arranged on an at least partially reflecting support surface 7.
  • an annular light source 3 Coaxial with the axis 4 of the objective 2 is an annular light source 3 with a defined diameter D and distance A to the support surface 7 is installed.
  • the light source 3 irradiates light 5 on an observation area of the support surface 7 with objects 6 arranged thereon.
  • the observation area is indicated schematically in FIG. 1 by the reference numeral 8 has a diameter B.
  • the light 5 is reflected at the curved surface of the objects 6 or after refraction on the curved surface on the support surface 7, and then extends substantially along the axis 4 to the lens 2.
  • an optical sensor 1 is arranged which detects the light coming from the observation area and takes a picture of the observation area.
  • FIG. 2 shows a cross-sectional view of an object, for example one of the objects 6 in the observation area 8 of FIG. 1, with illustrative beam paths of the light incident into the objective with the beam angles ⁇ 1 ⁇ , ⁇ 2 ⁇ and ⁇ 3tl .
  • an object a drop is shown in FIG.
  • the properties of other objects can also be determined by the method according to the invention.
  • the distance A and the distance of the objective from the observation area be large in relation to the diameter B of the observation area.
  • the light from the annular light source then arrives at each point of the observation area approximately at the constant angle of incidence a a ⁇ 2 a, 3 a ⁇ atan (-0.5 -D / A) and also leaves the observation area in the direction of objective 2 and optical sensor 1 Approximately constant angle ⁇ " ⁇ ⁇ 1 ⁇ , 2 ⁇ , 3 ⁇ ⁇ 0.
  • an evaluation circuit (not shown) is coupled to the optical sensor 1.
  • the evaluation circuit may be, for example, a processor that is operated with a calculation software for determining one or more object properties.
  • the image taken by the optical sensor 1 can first be stored in a memory and then evaluated, for example, on a computer.
  • Fig. 2 is for better clarity, only one possible beam path per reflection, ie per detected light component of the incident light, and not the mirrored at the axis 4 beam path.
  • the always observable reflection C 1 is formed by direct reflection of the light beam at the curved object surface 61 and corresponds to a first light component 51 of the light irradiated by the light source 3.
  • the reflection C 2 is formed by entry and refraction of the light beam at the object surface 61, reflection of the beam at the support surface 7 and exit from the object 6 with renewed refraction at the object surface 61.
  • the reflection C 2 thus corresponds to a second light component 52.
  • a third reflection C 3 may still be observable, which is produced by reflection of the light beam at the support surface 7 outside the object 6 and subsequent reflection at the object surface 61.
  • the third reflection C 3 corresponds to a third light component 53.
  • the optical sensor 1 in FIG. 1 is arranged such that the image taken by it captures the first, second and third light portions 51, 52, 53. From reflection and refraction law as well as from the contact angle and volume-dependent shape of the object 6, geometric relationships between the occurring reflection points or circles, ie the observable positions or shapes of the light components 51, 52, 53 in the image of the optical sensor, and derive the properties of the object 6. This means that from the observable and measured radii of Q and C 2, for example, the contact angle and the volume of the object 6 can be calculated. With the help of reflection C 3 as an additional measure, the result could even be validated at large contact angles.
  • the general geometric shape of an axisymmetric object 6 under the influence of gravity can be described by the Young-Laplace differential equation extended by the gravitational term:
  • ⁇ [N m “2 ] is the surface tension
  • Rj and R 2 [m] are the principal radii of curvature of the object surface 61
  • ⁇ [kg m “ 3 ] is the density difference between gas and liquid phases
  • z [m] is the vertical coordinate from the highest Point of the object
  • g [N kg "1 ] the acceleration of gravity
  • Ro [m] the radius of the radius at the highest point of the object
  • the equation can be simplified for axisymmetric objects and converted into a 1st order differential equation system.
  • the object profile is described by the coordinates x, z and ⁇ (see FIG. 2) as a function of the path length s [m] on the object surface and for a specific RQ:
  • the shape of the object 6 can be determined as a function of Ro. Only for a given R 0 and a certain height Ii of the object are the two measured reflection and refraction conditions fulfilled.
  • the profile of the object 6 can be determined from the size of the reflection or from its distance from the object axis. From the profile of the object and the height, the volume find of the contact angle of the object can then be calculated.
  • the dimensionless bond number Bo [-] describes the ratio of gravitational force to surface force and is usually formed with RQ as the characteristic length measure:
  • V ⁇ 2 R - (14)
  • the radii of the reflections Ci and C 2 can be determined by an automated image analysis from the images taken by the optical sensor.
  • the theoretically evaluable range of contact angles and object shapes is shown in FIG. 3 and depends on the angle of incidence a . Outside this range, the reflection C 2 is not observable.
  • the maximum deviation of the two measuring methods is about 1 °. This is within the scope of the estimated measurement accuracy of the conventional method. It should be noted, however, that even the conventional measurement of the contact angle is associated with a certain measurement error, resulting on the one hand by the manual evaluation of each image and on the other hand that the self-adjusting contact angle along the circumference, for example the inhomogeneous contact angle hysteresis is not necessarily constant. Due to the lateral projection of the 14,070,743
  • the contact angle for the conventional method can only be determined for two points. Since the curve of the method according to the invention has less fluctuations, with the method according to the invention, possibly even a higher measuring accuracy can be achieved than with the conventional method.
  • the accuracy of the method according to the invention is limited only by the inaccuracies in the geometric arrangement of the beam path, the simplification of the ideal shape of the object and the resolution accuracy of the microscope or the camera.
  • Fig. 4 shows images of a drop on a polycarbonate surface.
  • images of the droplet taken by the optical sensor 1 of FIG. 1 are shown, in which the reflections Cj and C 2 and partly also C 3 can be seen, ie the positions and shapes of the first, second and third detected light components
  • images of the droplet can be seen from the side, which were used to determine the contact angle according to the method known from the prior art.
  • the distance between the light source and the support surface and the distance between the support surface and the objective were 80 mm in FIG. 4 as well as in the following FIGS. 6, 8, 10 and 12.
  • FIG. 6 shows images similar to FIG. 4, on which the positions and shapes of the first, second and third detected light components are visible, as well as cross-sectional views of the droplet at different times, wherein the droplet is arranged on a hydrophobic surface.
  • FIG. 7 shows the contact angle with the images of FIG. 6 as a function of time, which were measured by the method according to one embodiment and the measuring method known from the prior art.
  • Fig. 7 shows that the invention also Verfaliren contact angle ⁇ > 90 ° can be applied, as long as the condition for the beam path of the reflection is fulfilled C 2, and this can be observed.
  • the measurement series for a drop on a hydrophilic surface shown in FIG. 9 likewise shows a very good agreement for small contact angles.
  • the automatic evaluation is only up to a contact angle of about 30 ° possible. To determine even smaller contact angles, the angle of incidence of the light source a a would have to be increased.
  • FIG. 10 shows images of a droplet under pronounced gravitational influence on a hydrophobic surface.
  • images of the droplet taken by the optical sensor 1 of FIG. 1 are shown, in which the reflections Ci ; C 2 and C 3 are visible, ie the positions and shapes of the first, second and third detected light components.
  • pictures of the drop can be seen from the side.
  • the course of the contact angle in the case of the droplet of FIG. 10 is shown comparatively for both methods, taking into account the influence of gravity during the evaluation on the hydrophobic surface.
  • the fiction, contemporary measurement method is suitable for determining the contact angle of a single object.
  • it has the advantage that objects can be measured even if they are located on concave supports, in depressions or in closed apparatus with a small optical access.
  • Another advantage of the method is that a large number of individual objects that are located in the observation area can be detected simultaneously by a numerical evaluation.
  • the object size distribution and the geometry of all present in the observation area and thus located in the captured image objects can be determined.
  • the specific condensation rate per area or the specific interface liquid-gas and liquid-solid can be determined in a condensation experiment.
  • An exemplary condensation test took place on a 2 mm thick disk of 50 ⁇ 50 mm polycarbonate, which was cooled at the bottom by an ethanol / water mixture at a temperature of -5 °.
  • the disc was overflowed with conditioned air (20 ° C, 40% rh) at a flow rate of 0.4 m / s in a small flow channel with a cross section of 60 x 50 mm.
  • the cooling water was turned off and the air velocity was increased to 15 m / s to defrost the disc.
  • the reflections Q and C 2 ie the first and second light portions 51, 52 were detected in the test evaluation by an automatic image recognition algorithm based on the software Matlab ® .
  • Each drop was assigned the inner reflection Ci and the outer reflection C 2 , ie the first and second light portions reflected or refracted at each drop were detected.
  • the bright ring-shaped or horseshoe-shaped Flexions correspond to the positions and shapes of the first and second light portions 51, 52 in the captured image.
  • the horseshoe shape is created by a partial occlusion of the annular illumination source and allows a good automation of the algorithm.
  • the reflection C ⁇ C compared to the reflection mirror 2, which is understandable based on the beam path in Fig. 2. This fact allows a distinction between the reflections and facilitates the correct assignment of the detected light components.
  • FIG. 13 shows a bar chart of the statistical distribution of the contact angle determined by the method according to the invention in the case of the above-described condensation test with a subsequent defrosting process on a polycarbonate surface.
  • the method according to the invention Since with the method according to the invention an at least as good measuring accuracy as with conventional methods can be achieved and the measuring error can be further reduced by multiple parallel measurements and averaging, a large part of the contact angle measurements made in the field of science and development could work with the method according to the invention. Since a lower technical complexity is required for the measuring method in comparison to conventional measuring methods, the method according to the invention also offers further technical advantages.
  • the vertical view of the one or more objects also creates new and simpler forms of application. This includes the quantitative analysis of the droplet condensation as shown in Fig. 14, which may play an important role especially in the observation of condensation processes in power plant technology. There can be achieved by drop condensation in contrast to the film condensation, a much higher efficiency of the capacitor. Furthermore, the fogging behavior of discs and other surfaces can be examined very closely. This is relevant, for example, in the examination of surfaces for refrigerated showcases, spectacles, or in the automotive industry, where the fogging of the disks is undesirable. reference numeral

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Abstract

L'invention concerne un procédé dans lequel au moins un objet est placé sur une surface de support au moins partiellement réfléchissante et une lumière est incidente à la surface de support et à l'au moins un objet placé sur celle-ci. Une première composante de la lumière incidente est réfléchie par une surface incurvée de l'au moins un objet et est puis détectée. Une seconde composante de la lumière incidente est réfractée par la surface incurvée lors de la pénétration dans l'objet, réfléchie par la surface limite entre l'objet et la surface de support, à nouveau réfractée par la surface incurvée lors la sortie de l'objet puis détectée. Une propriété de l'objet, comme par exemple un angle de contact entre l'objet et la surface de support, est déterminée à partir de la première composante de lumière détectée et de la seconde composante de lumière détectée. L'objet peut être par exemple une goutte ou une bulle. L'invention concerne également un dispositif et un support lisible par ordinateur.
PCT/EP2014/070743 2013-10-25 2014-09-29 Procédé optique et dispositif optique pour déterminer une propriété d'un objet partiellement transparent sur une surface de support partiellement réfléchissante, et support d'enregistrement lisible par ordinateur WO2015058927A1 (fr)

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CN106092828A (zh) * 2016-06-08 2016-11-09 清华大学 基于显微镜聚焦的接触角光学测量方法
US20210356372A1 (en) * 2020-05-14 2021-11-18 Krüss GmbH, Wissenschaftliche Laborgeräte Method and device for analyzing the interaction between a surface of a sample and a liquid
CN115248175A (zh) * 2021-04-28 2022-10-28 财团法人工业技术研究院 固体表面湿润性检测方法
US20220364854A1 (en) * 2021-05-11 2022-11-17 Xiamen University Of Technology Contact angle measuring device

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CN115248175A (zh) * 2021-04-28 2022-10-28 财团法人工业技术研究院 固体表面湿润性检测方法
US20220364854A1 (en) * 2021-05-11 2022-11-17 Xiamen University Of Technology Contact angle measuring device
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