Determining Forces of Interaction Between Macroscopic Bodies

The adhesion of microscopic particles may be judged from the character of the interaction between macroscopic particles and from the dependence of this on air humidity, particle size, surface properties, temperature, pressure, and other factors. Thus, the methods considered may be used for modeling the adhesion of microscopic particles. Attempts to use these methods for determining the adhesive forces of microscopic particles directly have not so far 5delded the desired results. The advantage of such methods lies in the fact that they may be employed for determining adhesive forces in so-called pure conditions (in air, in vacuum, etc.), and hence offer the possibility of obtaining reproducible results. 

In experiments intended to determine the forces of interaction between macroscopic particles one uses either two spherical particles of a diameter of the order of a few millimeters, or one such particle and a plane, or the fused ends of glass, quartz, or metal filaments (Fig. 11.12). The form of the ends may be rounded (a), spherical (b), or plane (c). 

The literature [43, 48, 79-84] contains descriptions of a number of pieces of apparatus in which the forces of interaction between spherical (or spherical and plane) surfaces coming into contact with one another are determined. Despite differences in structural formulation, all forms of apparatus contain the following principal units a spring or balance to which one of the bodies coming into contact is fixed, an arrangement for fixing the other body, and a reading device. 

These systems are usually quite small and are frequently placed in a special hermetically sealed space in which the temperature, humidity, and pressure may be varied. There are two types of apparatus, differing in the manner of detaching the particles. In systems of the first type [48, 79, 81, 82] a vertical plate (or sphere) is brought up to a freely hanging sphere or the fused end of a filament imtil contact occurs (Fig. 11.13). Then the plate is moved in a direction perpendicular to the area of contact. The deviation (angle a) of the suspended sphere from the vertical due to the action of the adhesive forces serves as a measure of the adhesion  

The angle a is either measured directly [48, 81, 82] or calculated from the deviation (measured with a micrometer) of the filament with the fused end from the original position (Fig, 11,14), This method is quite accurate, since the error of the method is determined by the accuracy of measuring the angle a. 

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Methods of Determining Forces of Interaction Between Macroscopic Bodies... 

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