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Basic principle and application of contact angle tester

  • Source: Unknown
  • Date: April 16, 2020
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The contact angle measuring instrument is mainly used to measure the contact angle of liquid to solid, that is, the wettability of liquid to solid. The instrument can measure the contact angle of various liquids to various materials. This instrument plays a very important role in scientific research and production of petroleum, printing and dyeing, medicine, spraying, mineral processing and other industries.
 
Definition of contact angle tester:
 
A professional measuring/measuring instrument specially used to measure the free energy of solid surface. Through platinum plate method, hanging drop method, inserting plate method and other principles, it can measure the contact angle value of one of the free energy expressions of solid surface accurately. At the same time, using software technology, it is possible to measure dynamic contact angle values, such as forward angle/backward angle, tilt angle, rotation angle, etc., as well as contact angle testing that changes with time.
 
Basic principle of contact angle tester
 
Because of different testing techniques, we can usually find many ways to test the contact angle of the contact angle tester. With these contact angle testing technologies, our factory can produce contact angle testers of various principles.
 
1. Image analysis method (goniometry) Contact angle tester:
 
The image analysis method is a simple method to measure or calculate the contact angle between the liquid and the solid surface through the image analysis technology by dropping a drop of liquid with the required volume on the solid surface. As an instrument for image analysis, its basic components are no more than light source, sample table, lens, image acquisition system and sample injection system. The simplest image analysis method can be obtained through the cross correction line in the lens directly tangent to the contact angle observed in the lens without image procurement system.
 
As an application of the dynamic contact angle test system, for example, we test the forward angle θ A and setback angle θ When R, we can control the injection volume, for example, we want to measure the advance angle θ A. We can increase the amount of liquid; If we want to measure the setback angle θ R, we can reduce the amount of liquid. Of course, we can also tilt the sample table to directly measure the tilt angle. At this time, we must use a high-speed camera for image acquisition. The standard image analysis system will adopt CCD camera and image acquisition system, and at the same time, contact angle value will be analyzed through software.
 
Advantages of image analysis contact angle tester
 
The image analysis method contact angle tester can use the environment much higher than the force measurement method, and we can easily measure the contact angle value of various shapes. The contact angle tester of force measurement method has higher requirements for the uniformity and flatness of materials. We can also be used to test the surface tension of samples under high temperature conditions, such as polymer after melting. This is the advantage of the image analysis contact angle tester, but the disadvantage of the image analysis contact angle tester is also obvious.
 
Disadvantages of image analysis contact angle tester
 
(1) The main defect of the image analysis contact angle tester is the large human error.
 
This defect is mainly due to: First, the reproduction ability of contact angle tangent is poor, mainly due to the user's artificial judgment error; Second, it is difficult to confirm the horizontal line, and the results will have large errors if the level of the horizontal line is different.
 
As a remedy for the above defects, the DR series contact angle tester uses software automatic analysis method to calculate the contact angle value. However, this method is also limited by whether there are miscellaneous spots in the test area. At the same time, the DR series contact angle tester uses a high-precision lifting table to control the consistency between the horizontal line of the sample table and the horizontal line of the software, so as to improve the recognition ability of the horizontal line in hardware mode. However, the horizontal line of this hardware correction may be different from the sample, and sometimes the horizontal line may not be observed.
 
(2) The repeatability of the sample injection process of the image analysis contact angle tester is poor during the forward and backward angle test.
 
In the process of droplet transfer, we usually inject more samples this time and less samples this time, and the change of such amount will also lead to the change of contact angle measurement value. Compared with the dynamic contact angle measured by force measurement method, this defect is very obvious.
 
(3) The image analysis contact angle tester cannot correctly test the fiber contact angle and powder contact angle values
 
 
2. Contact angle tester by inserting plate method:
 
It is also called tilting plate contact angle tester. Its principle is that when a solid plate is inserted into a liquid, the liquid level will stretch straight to the junction of three phases without bending until the included angle between the plate surface and the liquid is exactly the contact angle. Otherwise, the liquid level will bend. Therefore, change the insertion angle of the plate until there is no bending around the three-phase junction of the liquid level. At this time, the included angle between the plate surface and the liquid level is the contact angle. The inclined plate method avoids the difficulty of making tangent lines and improves the measurement accuracy, but the prominent disadvantage is that there is a large amount of liquid used. This hinders its application in many cases, and it can only test samples with contact angles less than 90 °. This is the contact angle tester based on this principle.
 
3. Tension contact angle tester:
 
This method is sometimes called Wilhelmy plate method for measuring contact angle. The contact angle tester using this method is mainly the contact angle tester of the contact angle tester testing system. The contact angle test is usually realized through the addition of software system. In the actual instrument purchase, the load cell in the contact angle tester is usually used, and the purpose of measuring the contact angle is realized through software analysis.
 
The specific principle is as follows: when a solid sample plate is immersed in the test liquid, due to the effect of the surface tension of the liquid and the surface free energy of the solid, the weighing sensor will sense a downward force F (Wettingforce). The specific calculation formula is as follows:
 
　　F= γ lgcos θ P。
 
Where: P represents the perimeter of the plate. If we know the measured force at this time, we can see the contact angle θ Value.
 
Of course, above we did not consider the buoyancy of the tested sample.
 
If we increase or decrease the immersion depth of the sample, we can measure the backward angle/forward angle.
 
Advantages of contact angle tester with force measurement method
 
(1) The force measuring contact angle tester can measure the uniform contact angle value of the whole sample through constant lifting plate.
 
(2) The contact angle tester of the force measurement method can measure the contact angle value of the dynamic system, mainly investigating the change with time. Especially, the contact angle hysteresis phenomenon can be better observed.
 
Disadvantages of contact angle tester with force measurement method
 
(1) The contact angle tester of force measurement method must first ensure that there is enough liquid to allow the sampler to be immersed;
 
(2) The contact angle tester sample of force measurement method must be removed, and it is better to know the geometric parameters such as perimeter and height.
 
(3) The force measuring contact angle tester requires that the sample be even, small and light enough. If the range of the sensor is exceeded, the test cannot be completed.
 
(4) The contact angle tester of force measurement method is greatly affected by temperature, and cannot measure the contact angle value under high temperature conditions.
 
4. Contact angle tester for transmission measurement:
 
The contact angle tester is mainly used to measure the contact angle of powder. The basic principle of this contact angle tester is that the gap between solid particles in the tube containing powder is equivalent to a bunch of capillary tubes. Capillary action enables liquid that can wet the surface of solid powder to penetrate into the powder column. Since capillarity depends on the surface tension of the liquid and the contact angle to the solid, measuring the permeability of the liquid with known surface tension in the powder column can provide knowledge of the contact angle of the liquid to the powder. In specific applications, we also divide it into two contact angle testers: the penetration height method (also known as the penetration balance method) contact angle tester and the penetration velocity method contact angle tester.
 
The above is the sharing of Dongyi Seiko on the "basic principle and application of contact angle tester". Shenzhen Dongyi Seiko Equipment Co., Ltd. specializes in the supply of stress testers, glass stress testers, Japanese original stress testers, fsm-6000le surface stress testers and other stress detection equipment, and provides professional laboratory solutions and equipment support services. Consulting hotline: 400-992-8117
 

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