MULTILAYER ADSORPTION WITH VARIABLE THICKNESS AT SOLID-LIQUID INTERFACES

The multilayer adsorption on the solid/liquid interface in binary mixt ures was studied by adsorption space filling with constant and variabl e layer thickness. Adsorption from benzene/n-heptane mixtures was exam ined on hydrophilic and hydrophobic surfaces. The free enthalpy of ads orption, Delta(21)G=f(x(1)), was calculated from the adsorption excess isotherm by integration of the Gibbs equation. Supposing that the fre e enthalpy is mainly due to adsorption in the first layer, the composi tion of this layer can be calculated from the Delta(21)G=f(x(1)) funct ion. It was established that the adsorption layer thickness in benzene /heptane mixtures increases significantly with increasing benzene cont ent. This statement was supported by X-ray diffraction on hydrophobic clay minerals.