JP2012208075A - Measuring method of contact angle on solid surface and system therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method of a contact angle on a solid surface and a system therefor, in which a droplet of a constant volume is placed on a surface of a subject to be measured, a contact area of the droplet in contact with the surface of the subject to be measured is measured, and an average contact angle of the droplet is calculated based on the volume and the contact area of the droplet.SOLUTION: Even when a droplet has any shape, the contact angle of the droplet can be measured only by measuring the volume and the contact area of the droplet. A contact configuration of the droplet on the surface of the subject to be measured viewed from the top in the vertical direction (plainer view) is recorded, and the contact area thereof is measured; thereby the contact angle can be measured even in an area of high hydrophilia at contact angle of 80° or less with a simple and highly reliable manner.

Description

    The present invention relates to a method for measuring a contact angle of a solid surface and an apparatus therefor, which is used for measuring a contact angle in a range of 0 ° to 90 °, for example, for evaluating the hydrophilicity of a solid surface.

    In order to prevent corrosion, deterioration of function, and contamination due to rainwater, moisture, etc., many articles have their surfaces protected with a coating film or the like. This measure is especially important for automobiles, building outer walls, window glass, etc., which are constantly exposed to harsh environments such as outside air and wind and rain. In recent years, coatings used for such applications have been required to have water repellency that repels water and liquids, or hydrophilic properties that are completely opposite to these. Conventionally, a method for evaluating these properties is generally a method represented by a contact angle between a liquid and an object to be measured (solid).

    Many conventional contact angle measuring devices capture a droplet cross-sectional image as an optical image from a lateral direction of a droplet on a solid surface, and directly measure the contact angle from the cross-sectional image. Recently, a method of calculating the contact angle of a droplet on the sample surface from this value and the value of the droplet volume after the droplet is imaged from above and the diameter of the droplet image is calculated by computer image analysis ( JP-A-5-232009) or a method of measuring the height of a droplet on a sample by a non-contact distance measuring means such as a laser microscope and obtaining a contact angle from a measured value of the droplet diameter by another method (JP-A-8-2008). 5008), a method of obtaining a contact angle by dropping a droplet having a constant volume on a sample and measuring the projected diameter of the droplet with a camera from above the sample (JP-A-1-126523).

    In recent years, by using Rayleigh-type surface acoustic waves, the liquid is excited by exciting the surface acoustic waves, and the frequency and attenuation rate of the free vibration of the liquid droplet after the excitation is stopped are measured. There are also reports on the measurement of the viscosity, surface tension and contact angle.

    Furthermore, recently, the present inventors have invented a method for measuring the contact angle from the free frequency of the droplet on the object to be measured, and have applied for a patent (Japanese Patent Laid-Open No. 2009-36634). Compared with the conventional method of obtaining the contact angle from the liquid droplet cross-sectional image, this method is very stable in the measured value of the contact angle of 80 ° or more indicating water repellency, and can be measured with high accuracy without any human error. In addition, even if the contact surface is not a perfect circle, it is a very excellent measurement method, such as a curved surface, and measurement within a concave surface where conventional measurement is impossible.

JP-A-5-232009 JP-A-8-5008 Japanese Patent Laid-Open No. 1-126523 JP 2009-36634 A

    However, in each of the first three methods described above, the measuring device requires an imaging device, a measured object position adjusting device, an image display device, etc., which are generally expensive and are subject to measurement. There are restrictions on the size of objects, measurement positions, etc. In addition, it is very difficult to accurately identify the state of the solid-liquid interface in the measurement. In particular, the stronger the hydrophilicity (the smaller the contact angle), the droplet shape on the object to be measured is not necessarily a part of a true sphere but a distorted shape such as a part of an elliptical sphere. All of the conventional measurement methods are measurement methods that are established by assuming that the droplet is a part of a true sphere, and thus have the disadvantage that the accuracy and reliability of the measurement values are not always satisfactory.

    Further, in the conventional method using the Rayleigh type surface acoustic wave, the physical property of the liquid on the piezoelectric substrate capable of exciting the surface acoustic wave is measured, and the surface acoustic wave can be excited as an individual. However, there is a limitation that the shape and size that can be measured from the optical structure is limited, and the apparatus becomes large and is not a simple method.

    Further, in the conventional method of the present applicant, in the hydrophilic region where the contact angle is 80 ° or less, the vibration amplitude becomes small and the change in the free frequency with respect to the change in the contact angle becomes minute, so that measurement is difficult. It had the inconvenience of being.

    An object of the present invention is to eliminate these disadvantages.

    In order to solve the above problems, the inventors have conducted intensive research. Then, paying attention to the adhesion shape and adhesion area of the droplet and the surface of the object to be measured, the relationship between the area of the droplet contacting the solid interface and the contact angle is clarified. A solid surface contact angle measuring method and apparatus capable of measuring a contact angle between materials have been devised.

    In the contact angle measurement method for a solid surface according to the present invention (invention 1), a droplet having a constant volume is placed on the surface of the object to be measured, and the contact area of the contact surface of the droplet with the surface of the object to be measured is determined. An average contact angle of the droplet is calculated from the volume of the droplet and the contact area.

    In this case, the contact area can be obtained by converting the contact area into an area of a circle equal to the area (claim 2).

    Further, in this case, the average contact angle is converted into the area of a circle with the maximum diameter inscribed in the shape of the contact surface, the contact angle based on the contact area determined and the minimum circumscribed in the shape of the contact surface. It can also be expressed as being sandwiched between contact angles based on the contact area determined by converting to the area of a circle of diameter.

    Further, in these cases, the droplets can be colored (claim 4).

    Further, in the solid surface contact angle measuring device according to the present invention (invention 5), the droplet placing means on the surface of the object to be measured, and the contact area measuring means of the droplet on the surface of the object to be measured; And a contact angle calculating means for calculating an average contact angle of the droplet from the volume of the droplet and the contact area.

    In this case, it is possible to provide contact angle measuring means (invention of Japanese Patent Application Laid-Open No. 2009-36634) for measuring the contact angle by the free frequency of the droplet on the object to be measured.

    Since the method for measuring the contact angle of the solid surface according to the present invention (invention 1) is configured as described above, that is, a droplet having a constant volume is placed on the surface of the object to be measured, and the measurement of the droplet is performed. The contact area of the contact surface with the object surface was measured, and the average contact angle of the droplet was calculated from the volume of the droplet and the contact area. The contact angle of the droplet can be measured only by measuring the volume and the contact area.

    Therefore, if this measurement method is used, the adhesion shape (planar state) of the droplet on the surface of the object to be measured is recorded from above and the contact area is measured, so that the hydrophilicity with a contact angle of 80 ° or less is obtained. Even in a strong region, the contact angle can be measured by a simple and reliable method.

    In this case, as shown in claim 2, if the contact area is converted into an area of a circle equal to the area, the contact area can be easily measured, and can be measured more easily. .

    According to a third aspect of the present invention, the average contact angle is converted into an area of a circle with the maximum diameter inscribed in the shape of the contact surface. If it is expressed as being sandwiched between the contact angle based on the contact area obtained by converting to the area of the circle with the smallest diameter circumscribing the shape, the contact surface shape, which was conventionally difficult to measure, is a perfect circle. The effect which provides the effective means which represents the contact angle of what is not can be show | played.

    Further, in these cases, as shown in claim 4, when the droplet is colored, when the contact area of the droplet is measured, the object to be measured and the droplet are clearly identified in the image of the digital microscope. It is easy to measure.

    In addition, since the solid surface contact angle measuring device according to the present invention (invention 5) is configured as described above, that is, the droplet placing means on the surface of the object to be measured and the surface of the object to be measured. The droplet contact area measuring means and the contact angle calculating means for calculating an average contact angle of the droplet from the volume of the droplet and the contact area are provided. Can be implemented.

    In this case, as shown in claim 6, if a contact angle measuring means for measuring the contact angle by the free frequency of the droplet on the object to be measured is provided, the above method (claim) is provided. In 1 to 4), it is possible to measure a contact angle of 90 ° or more, which is difficult to measure, and the use value is expanded.

    Further, the effects of the present invention will be described in detail with reference to FIGS.

    Each of these figures shows an example of a droplet adhesion shape on the solid surface observed from above the surface of the object to be measured. FIG. 7 shows an observation image of the plastic surface using water droplets having a liquid volume of about 6 μl. And the contact angle is in the vicinity of 90 °. At first glance, the contact surface looks like a perfect circle, but it can be seen that the shape measurement is not a perfect circle. FIG. 8 is an observation image of the surface of a metal material that has been rolled and polished using a water droplet having a liquid volume of about 6 μl. The contact angle was observed to be around 60 degrees.

    As described above, the shape of the droplet on the solid surface is not necessarily a part of a true sphere, but greatly depends on the state of the solid surface. Therefore, although the conventional method (JP-A-5-0232009) for measuring a contact angle by observing a droplet from the lateral direction exhibits such a shape, the contact angle measurement includes many errors. Similarly, in the method of obtaining the contact angle by calculation from the value of the diameter of the droplet image when a droplet of a certain volume is observed from vertically above the solid surface (JP-A-5-232009), Since it is handled as a part of the sphere, the contact angle of the liquid droplet deviated from the true sphere includes a large error or cannot be measured.

    As described above, in the conventional measurement method, when the droplet cannot be regarded as a part of the true sphere on the surface to be measured, the measurement becomes difficult. However, in the present invention, such a droplet shape deviates from the true sphere. In this case, the contact shape of the droplet is recorded, and the average contact angle is expressed by assuming an average circle from the contact area of the contact shape, or photographed using the method according to claim 3. Regions that would have been impossible to measure or represent in the past if the contact angle was expressed by sandwiching it between two contact angles calculated from the area of the inscribed circle and circumscribed circle in the actual image representing the adhesion shape of the droplet It is possible to evaluate the surface properties of the object to be measured with respect to the required liquid.

    The solid surface contact angle measuring method and apparatus according to the present invention have the following main features when implemented.

    When a fixed volume droplet is placed on the surface of the object to be measured, it is performed by a micro syringe, a micro pipette, or a droplet dropping device (droplet placing means). In this case, the volume of the droplet is about 1 to 7 μl, and when it is colored, a complementary color of the surface color of the object to be measured is suitable, but it is sufficient if the contrast between the surface to be measured and the droplet can be obtained.

    When measuring the contact area of the contact surface of the liquid droplet to the surface of the object to be measured, observe and record the adhesion shape (planar view state) of the liquid droplet on the surface of the object to be measured from above using a digital microscope. Then, the contact area is measured from the plan view (contact area measuring means). The contact area is measured on a personal computer. Specifically, it is calculated from the ratio of the number of pixels occupied by the droplet contact area to the number of pixels occupied by the entire visual field area with a constant magnification of the digital microscope. To do. In addition, the value of this contact area can also be converted into the area of a circle equal to the area.

    When measuring the average contact angle of the droplet, it is calculated on a personal computer from the volume of the droplet and the contact area (contact angle calculation means).

    The basis of the theory for calculating the average contact angle of the droplet from the volume of the droplet and the contact area by the contact angle calculation means will be described.

    The inventor of the present invention clearly understands that if the volume of the droplet is known, the contact angle of the droplet contacting the solid surface can calculate the contact surface area with the solid assuming that the droplet shape is part of a sphere. did. In addition, it is easily predicted that the droplet does not become a part of the true sphere, particularly in a region where the contact angle is small, but in such a case, if the contact state of the droplet becomes clear, the droplet contacts the droplet. We have found that useful data for contact angles between objects, average contact angles based on contact shapes can be provided.

As for the relationship between the droplet adhesion area on the solid surface and the average contact angle, as shown in FIG. 3, the contact angle of the adhered droplet is a part of a true sphere with 90 ° or less (θ <90 °). Assuming that the contact angle Θ in this condition is given by the following equation from the droplet volume and the solid surface adhesion area of the droplet.

    Here, S is the solid surface adhesion area of the droplet, V is the droplet volume, and θ is the contact angle. FIG. 4 shows the relationship between the average contact angle and the value obtained by standardizing the cube of the droplet adhesion area on the solid surface by the square of the volume based on the formula (1). From this figure, as the contact angle becomes smaller, the contact area increases exponentially, that is, the smaller the θ is, the more sensitive measurement is possible. In FIG. 3, ρ is the contact surface radius of the droplet, h is the height of the droplet, θ is the contact angle, and r is the radius when the droplet is assumed to be a true sphere.

    In addition, this measuring apparatus is provided with contact angle measuring means for measuring the contact angle by the free frequency of the droplet on the object to be measured, and the above method (Claims 1 to 5) can be performed with one apparatus (shared with a personal computer). Then, it is possible to measure a contact angle of 90 ° or more, which is difficult to measure.

    Embodiments of the present invention will be described below with reference to the drawings.

    1 is a schematic diagram of an embodiment of a solid surface contact angle measuring apparatus according to the present invention, FIG. 2 is a schematic diagram of another embodiment, and FIG. 3 is a liquid on a solid surface when the contact angle θ <90 °. FIG. 4 is a schematic diagram showing a droplet, FIG. 4 is a graph showing the relationship between a value obtained by standardizing a droplet adhesion area on a solid surface by its volume, and an average contact angle, and FIG. 5 shows this average contact angle from an actual image of a droplet. FIG. 6 is a schematic diagram showing a method for calculating, FIG. 6 is a schematic diagram showing a method for determining the existence range of the contact angle of the droplet from the actual image of the droplet, and FIG. 7 is an example of the droplet adhesion shape image on the solid surface. FIG. 8 is a photograph showing another example.

Examples and the like will be described below, and the embodiments of the present invention will be described in more detail. FIG. 1 shows an embodiment of the invention of claims 1 to 5, wherein 4 is an object to be measured (for example, a metal surface), and 3 is a fixed amount (about 1 to 7 μl) of droplets dropped on the surface. is there. When it is difficult to clearly distinguish the object 1 and the droplet 3 from each other, the droplet 3 is colored by a complementary color of the surface of the object to be measured or by a color having a strong contrast with the surface of the object to be measured. Alternatively, it is dropped by a droplet dropping device. Reference numeral 1 denotes a digital microscope (contact area measuring means), which is arranged above the object to be measured 4. The digital microscope 1 captures the droplet 3 at a required magnification (for example, 50 times) from vertically above, and displays and records this image on the screen of a personal computer (PC) (contact area measuring means) 2 through the USB connection 5. To do. The area of the adhesion shape image of the recorded droplet 3 on the surface of the object 4 to be measured is calculated by software written in advance on a PC (contact angle calculation means) 2, and the contact angle θ is applied to the solid surface shown in FIG. The droplet contact area is obtained from the relationship between the value (vertical axis) normalized by the volume and the average contact angle (horizontal axis). The colorant for coloring the droplet 3 is provided for clearly identifying the object to be measured 1 and the droplet 3 in the image of the digital microscope 2. It shall not affect the surface tension value.
A specific example (see FIG. 8) will be described. Uncolored, 6 μl of water droplets 3 were dropped on the surface of the plastic 4 which had been surface-treated by the dropping device. The droplet 3 is captured at a required magnification (approximately 50 times) from above by the digital microscope 1, and this image is displayed and recorded on the screen of a personal computer (PC) (contact area measuring means) 2 by the USB connection 5. PC (contact angle calculation means) 2 calculated that the area was 6.9 mm ² from the ratio of the number of pixels occupied by the droplet contact area to the number of pixels occupied by the entire visual field area. Based on this area, the contact angle was measured to be 85 ° from the graph of FIG.

    The obtained average contact angle is displayed on the PC2 screen together with the adhesion shape image, so that the adhesion situation of the solid surface to the droplet and the average contact angle can be shown.

    The digital microscope 1 has a function of taking a snapshot of necessary images, a video function of continuously shooting, and an interval function of shooting at a constant time interval, and this function is properly used according to the purpose. For example, when the liquid is absorbed by the material 4 to be measured over time, the time series change of the droplet 3 can be observed and measured by using the video function or the interval function.

FIG. 5 is a view for explaining the invention of claim 2. 8 is a real image representing the adhesion shape of the droplet 3 photographed by the digital microscope 1, and 9 is a circle having the same area. In the invention of claim 1, as shown in FIG. 5, the method for calculating the average contact angle of the droplet 3 is the method of calculating the volume of the droplet 3 and the droplet 3 in contact with the individual surface photographed by the digital microscope 1. The average contact angle obtained by converting the image into an area of a circle equal to the area is displayed on the PC 2 screen together with the image of the droplet 3. In the conventional method, the contact angle varies depending on the observation direction, but in this method, the average contact angle is expressed.
In the case of the specific example, it is converted into a circle with a radius of 1.48 mm.

FIG. 6 shows an embodiment of the third aspect of the present invention. 8 is an actual image representing the adhesion shape of the droplet 3 photographed by the digital microscope 1, 10 is a maximum inscribed circle inscribed in the actual image, and 11 is a minimum inscribed circle circumscribed in the actual image. In the first aspect of the invention, the way of expressing the contact angle is calculated from the area of the inscribed circle 10 and the circumscribed circle 11 in the real image representing the adhesion shape of the photographed droplet 3 as shown in FIG. The contact angle is calculated and expressed in a form sandwiched between two contact angles.
In the case of the above specific example, the contact angle of the area of the inscribed circle (radius 1.47 mm)
It is expressed as a state (84.7 ° ≦ θ ≦ 85.9 °) sandwiched between 85.9 ° and a contact angle of 84.7 ° in the area of a circumscribed circle (radius 1.49 mm).

    FIG. 2 shows an embodiment of the invention of claim 6. 1 is a digital microscope, 2 is a PC, 3 is a droplet, 4 is an object to be measured, 5 is a USB connection of the digital microscope, 6 is a droplet vibration contact angle measuring device detector, and 7 is a droplet vibration contact angle measurement The apparatus detection part output signal transmission medium is represented. In the invention of claim 5, by combining these inventions with a droplet vibration type contact angle measuring device, the contact angle measurement which is a weak point of the inventions of claims 1 to 5 is a droplet vibration type. By using the contact angle measuring device (invention of JP 2009-36634 A), the invention of claim 5 is limited to the measurement with a contact angle of 90 ° or less, thereby expanding the measurement area and sharing the PC 2. The contact angle measuring device has a simple configuration.

The solid surface contact angle measuring method and apparatus according to the present invention measure the contact angle of a liquid droplet only by measuring the volume of the liquid droplet and the contact area, regardless of the shape of the liquid droplet. Therefore, even in a highly hydrophilic region having a contact angle of 80 ° or less, the contact angle can be measured by a simple and reliable method. Therefore, industrial applicability is high, for example, when the property of the solid surface is evaluated by the contact angle.

FIG. 1 is a schematic view of an embodiment of a solid surface contact angle measuring apparatus according to the present invention. FIG. 2 is a schematic diagram of another embodiment. FIG. 3 is a schematic diagram showing droplets on the solid surface when the contact angle θ <90 °. FIG. 4 is a graph showing the relationship between the average contact angle and the value obtained by standardizing the droplet adhesion area on the solid surface by its volume. FIG. 5 is a schematic diagram showing a method for calculating the average contact angle from the actual image of the droplet. FIG. 6 is a schematic diagram showing a method for determining the existence range of the contact angle of the droplet from the actual image of the droplet. FIG. 7 is a photograph showing an example of a droplet adhesion shape image on a solid surface. FIG. 8 is a photograph showing another example of the droplet adhesion shape image on the solid surface.

1 ... Digital microscope (contact area measuring means)
2 ... Personal computer (contact area measuring means) (contact angle calculating means)
DESCRIPTION OF SYMBOLS 3 ... Droplet 4 ... To-be-measured object 5 ... USB connection 6 ... Droplet vibration type contact angle measuring device detection part 7 ... Droplet vibration type contact angle measuring device detection part Output signal transmission medium 8 ... Schematic diagram of a droplet adhesion image 9 ... Circle equal to the adhesion area of the droplet 10 ... Inscribed circle of the droplet adhesion image 11 ... circumscribed circle of the droplet adhesion image

Claims (6)

A droplet having a constant volume is placed on the surface of the object to be measured, and the contact area of the contact surface of the droplet with the surface of the object to be measured is measured. A method for measuring a contact angle of a solid surface, wherein the angle is calculated. 2. The method for measuring a contact angle of a solid surface according to claim 1, wherein the contact area is obtained by converting into an area of a circle equal to the area. The contact angle based on the contact area obtained by converting the average contact angle into the area of a circle with the maximum diameter inscribed in the shape of the contact surface, and the area of the circle with the minimum diameter circumscribed in the shape of the contact surface The contact angle measurement method for a solid surface according to claim 1, wherein the contact angle is expressed as being sandwiched between contact angles based on contact areas obtained by conversion into 4. The method for measuring a contact angle of a solid surface according to claim 1, wherein the droplet is colored. Means for placing the droplet on the surface of the object to be measured, means for measuring the contact area of the droplet to the surface of the object to be measured, and the volume and the contact area of the droplet, and calculating the average contact angle of the droplet A solid surface contact angle measuring device comprising a contact angle calculating means. 6. The apparatus for measuring a contact angle of a solid surface according to claim 5, further comprising contact angle measuring means for measuring a contact angle based on a free frequency of the droplet on the object to be measured.

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