Contact interactions lyophobicity

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... 

For typically lyophobic systems (e.g. aqueous dispersions of solid hydrocarbons) with a characteristic value of A 5x 10 20 J at r 10 8 m and h0 2x1 O 10 m the interaction energy between particles in a contact, in agreement with eq. (VII. 15), is not less than... 

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]... 

The results obtained by Mukerjee and Handa substantiate the fundamental difference between liquid-air and liquid-liquid interfaces. The surface tension of a surfactant solution depends mainly on interactions with the solvent and adsorption at the liquid-air interface. Interactions with air or vapor are weak. In contrast, a surfactant at a liquid-liquid interface interacts with two liquid phases. The lyophobic part of a surfactant oriented away from one of the liquid phases interacts with the second liquid phase in contact. The interaction between the lyophobic film and the second liquid phase is much more significant than the interaction with air or a vapor. 

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