PREFERENTIAL ADSORPTION ON POROUS-GLASS NEAR THE LIQUID LIQUID COEXISTENCE CURVE OF A BINARY-LIQUID MIXTURE/

A differential refractometric method is used to study the temperature and composition dependence of preferential adsorption of water on the surface of pore-controlled glass out of 2-butoxyethanol (abbreviated C (4)E(1))/water mixtures. The experiments are carried out close to the liquid/liquid coexistence curve in the vicinity of the lower critical point of the system. When the temperature of phase separation T-p of t he mixture is approached at (almost) constant bulk composition from te mperatures below T-p the amount of substance of adsorbed water (n) ove r tilde(w)(s) per unit mass of adsorbent extrapolated to T-p increases along the liquid/liquid coexistence curve with increasing values of x degrees (x degrees, mole fraction of C(4)E(1) of the mixtures before adding the absorbent). In experiments with mixtures of composition x d egrees>x(c), the quantity (n) over tilde(w)(s) is about 10 times large r than that found in experiments with mixtures of compositions x degre es<x(c) (x(c), critical composition). The data are interpreted by pres uming that the extent of the preferential adsorption of water and its temperature and composition dependence is primarily caused by the pres ence of -SiOH and -SiO- groups at the hydrophilic surface of the adsor bent [and H+(aq) counter ions] in combination with concentration fluct uations occurring in a wide range of temperatures and compositions alo ng the binodal curve. (C) 1996 American Institute of Physics.