Adhesion in Solutions of Surface-Active Substances

Variations of adhesion in liquid media in the presence of organic acids and alcohols and surface-active substances (SAS) possessing detergent properties were studied in [8, 59, 76]. 

The results of some experiments [8] into the adhesion of quartz particles in solutions of various organic acids are presented in Fig. IV.16. For weakly concentrated solutions (concentration up to 1 mole/liter) the maximum adhesion occurs in solutions of formic acid. On increasing the velocity of electrophoresis (and hence the f potential) adhesion is reduced. Thus, the minimum adhesion of quartz particles occurs in a solution of propionic acid, the velocity of electrophoresis being greatest for this. 

The adhesion of particles falls with increasing density and thickness of the diffusion and adsorbed layers of the acid solutions, and this in turn depends on the position of the saturated acids in the homologous series. 

For a concentration higher than 7 mole/liter, the situation is the opposite to that shown in Fig. IV.16. Adhesion reaches its maximum value in the solution of propionic acid. 

Adhesion in aqueous solutions of alcohols is also determined by the position of the alcohol in the homologous series. 

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The addition of such electrolytes as KCl and BaCl2 in quantities not exceeding 0.1 mole/liter to solutions of propyl, ethyl, and methyl alcohols leads to an increased adhesion. We noted something rather similar (Fig. IV.18) when studying adhesion in solutions of surface-active substances (commercial products containing small quantities of electrolytes). The fact that the adhesive forces in solutions of T Duomin, NT Armak, and sodium oleate exceed the expected values may clearly be attributed to the presence of such electrolytes. 

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