APPARENT NEGATIVE ADSORPTION OF SODIUM CH ONDROITIN-6-SULFATE AND SODIUM CARBOXYLATOMETHYL-CELLULOSE BY AMORPHOUS SILICA IN THE PRESENCE OFPOLY(N-VINYLPYRROLIDONE) OWING TO THE WATER THAT PENETRATES INTO THE SURFACE PORE AND INTERPARTICLE VOID SPACE

Adsorption amounts, obtained from the differences between initial and equilibrium concentrations, of sodium chondroitin-6-sulfate and sodium carboxylatomethylcellulose by silica Micon FN from an aqueous solutio n of 0.9% NaCl exhibited negative values in the presence of poly(N-vin ylpyrrolidone). Surface pore and interparticle void space due to the a ggregation of Micon FN were responsible for the negative adsorption. W ater molecule could penetrate into them while polymer molecule could n ot owing to its large size, resulting in concentrating the polymer in the bulk phase during the adsorption. Three methods to estimate the vo id volume were theoretically and experimentally developed: (1) 2-steps dilution methods, by determining the polymer concentration in the sup ernatants before and after dilution with a known amount of the solvent ; (2) graphic method, through determining the negative slope of an iso therm of apparent/negative adsorption; and (3) Na+-activity method, by measuring the Na+-activity in the presence of known amounts of a poly mer and Micon FN. The void volumes (V-p), estimated through these 3 me thods, conincided each other (V-p=2-6 ml/g of Micon FN). The true amou nts of adsorption became positive after the correction by using V-p.