.iDSORPTIOK FRORl LIQT’ID JIISTT‘TtES *IT SOTAIDST’RFACES * T:R \ V I )
.J. .J. I < I E L I ~ I ( ~
Department of Chenustry, l‘he linzv Received liay 6 , I969
There are a t least four major factors which appear to be important in considering adsorption from the liqiiid phase onto solids: ( a ) the thickness of the adsorbed film, ( b ) the orientation of the adsorbed molecules, ( c ) the polarit1 of the solid surfaces, ( d ) the interaction between the liquid components These factors probably are relevant in the choice of solntes drsigned to stabilize dispersions Adsorption by charcoal from mixtures of benzene with each of the lower aliphatic alcohols is considered in the light of these four factors. Adsorption can be interpreted as being confined to a monolayer, the alcohol molecules being adsorbed with the major axis parallel to the solid surface. The competitive adsorption is affected both by interaction between the liquid components and by strong interaction between the alcohol molecules and oxide complexes on the adsorbing surface.
Introduction The ctabilizing of dispersions of solids in liquid media is usually dependent on the adsorption of a solute from the liquid a t the interface. The adsorbed material frequently may be ionic in character, but a number of cases of non-ionized substances ( e . g . , polyvinyl pyrrolidone, alkylated aromatic hydrocarbons1) and of substances with only a small ionic contribution (e.g., gum arabic) are important. Although the adsorption of high molecular weight and especially of polymeric substances may iiirolve factors not present in the adsorption of simpler compounds,2me believe the fundamental informa tiori which can be obtained from a study of simple systems to be relevant to the question. Bartell and Murray hare pointed out the close connection between preferential adsorption from binary mixtures of simple compounds and stability of suspeii40ns.3 Consideration of published work on adsorption hy solids from binary mixtures of simple non-electrolytes suggests that the following points are important : (1) whether the adsorbed film is one or several niolecules thick; ( 2 ) the orientation of the adsorbed material at the interface; ( 3 ) the polarity of the solid surface; (4) the interaction between the two liquid components; in the case of limited miscibility. the nature of the “solvent.” As yet, the amount of fundamental information of this kind on the more complex systems of practical importance is very small. Increasing attention is heing paid, however, to relatively simple systems and it may lie hoped that this will provide a basis for understanding the type of adsorption which is important in rolloidal and rheological fields. We therefore present results which have been obtained with t n o-component systems. the two substances k i n g miacible over the entire concentration range. I3enzene was u
