Contact interactions lyophilicity

Equation 1.44 is a reasonably smooth function, which is an indication that dispersion interactions compensate each other to a significant extent, even when there is a large difference in the nature of the contacting phases. For example, if both Aj and A2 are around 10 ° J and differ from each other by, for example, 20%, then A 10 J for a 5% difference. A 2.5 x 10 J, and for a 2% difference between A, and A2, A is lowered to 10 J. We will use these estimates later in the characterization of the contact interactions in lyophilic and lyophobic systems. 

The described experimental method for measuring the contact interactions between solid particles influenced by surfactant adsorption from various electrolyte solutions allows one to observe transition from lyophilicity to lyophobicity and to study the role of the electrolyte in this transition. 

The methods and quantitative characteristics used in the analysis of the contact interactions between the particles can be applied to the processes involving the formation of sediments. This can be verified experimentally in sedimentation experiments with hydrophobic spherical particles (e.g., methylated glass or fluoropolymers) in a medium of a different polarity. The sedimentation of hydrophobic particles in low-polarity media, such as propanol or butanol, is of lyophilic type. The sedimentation of such particles in polar media, such as water or ethylene glycol, follows the lyophobic scheme. Similar to the case of experimental contact interaction studies, one can also observe a gradual transition from one type of sedimentation to the other. One particnlar example is the sedimentation of hydrophobic particles in aqueous solutions of alcohols. As the system becomes more lyophilic with the shift to alcohols with lower polarity or with an increase in the alcohol concentration, a transition from lyophobic sedimentation to lyophilic sedimentation takes place. A gradual decrease in the volume of the sediment is observed. Small additives of surfactants that make the surface of the particles hydrophilic have a similar effect. The concentration of an alcohol... 

TABLE IX. 1. Free energy of interaction (cohesion), lAA, in contacts between moleculary smooth hydrophilic and hydrophobic spherical particles with radii, r of 1-2 mm in different polar and non-polar media ( extreme cases of lyophilicity and lyophobicity) [17, 19,22]... 

In our concluding remarks we can emphasize that depending on the nature of interactions between the components that constitute the medium and the solid, as well as on a combination of external conditions, one may observe the effects of various types and intensity. These include the facilitation of plastic flow of solids, or, alternatively, brittle fracture due to the action of lowered stresses mechanochemical phenomena in the zone of contact mechanically activated corrosion (the stress corrosion) the processes that are close to the spontaneous dispersion (the so-called quasi-spontaneous dispersion), and the true spontaneous dispersion, leading to the formation of thermodynamically stable lyophilic system. A great variety of types of interactions that exist between the stressed solids and the medium in contact with it requires careful and thorough examination of conditions under which... 

Because of the high computing power of modem computers, a molecular dynamic experiment can involve the simultaneous investigation of the motion and interaction of millions of molecules (atoms). In Section 4.2, we will leam in greater detail one of the studies in which the breaking of the contact between two small particles was observed under conditions of complete lyophilicity, allowing for a spontaneous penetration of liquid into the contact zone between the particle and the surface of the same nature. 

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