EFFECT OF SURFACE GEOMETRY ON ADSORPTION AND DESORPTION OF POLYMER-CHAINS

Adsorption and desorption of polystyrenes (PS) at three different porous silica surfaces in cyclohexane have been performed in order to examine the effect of surface geometry on the adsorption and desorption phenomena of polymer chains as a function of the size ratio of the average pore diameter to twice the radius gyration of a PS chain. Dioxane was used as the displacer molecule. The adsorption isotherms for the porous silica surfaces are almost the same as for the nonporous silica in their shape. However, the plateau adsorbed amount increases with an increase in the size ratio. A similar surface geometry effect is also observed for the desorption of polystyrenes by dioxane. These phenomena can be interpreted in the terms of the surface fractal when the whole polymer chain is regarded as the yardsticks. The critical concentrations of the displacer molecule at which all PS chains can just be desorbed is almost independent of the pore size and the molecular weight of PS.