Adsorption characteristics of poly(acrylic acid) and poly(vinyl pyrrolidone) on titanium dioxide modified with quaternary ammonium groups

Abstract

Adsorption of poly(acrylic acid) and poly(vinyl pyrrolidone) on titanium dioxide modified with quaternary ammonium groups (XNm, m is the carbon number of the alkyl chain, 8 and 16) has been studied at pH 5.2 and 10.2 by measuring amount adsorbed, ζ potential and dispersion stability. The conformation of the adsorbed polymer is also estimated using spin-labeled polymers. In the case of poly(acrylic acid), the amount adsorbed is greater for XN8 than those for both XN16 and untreated TiO2 at pH 5.2, while at pH 10.2 it is very small for the three samples. On the other hand, adsorption of poly(vinyl pyrrolidone) increases in the following order: untreated TiO2>XN8>XN16 at both pH where the amount adsorbed is greater at pH 5.2 than that at pH 10.2. Adsorption of poly(acrylic acid) is mainly attributed to electrostatic forces, while that of poly(vinyl pyrrolidone) is facilitated by hydrogen-bonding for untreated TiO2 and by hydrophobic interactions for both XN8 and XN16. The ESR measurements indicate that poly(acrylic acid) and poly(vinyl pyrrolidone) adsorb on XN8 and XN16 mainly as train segments in a whole concentration region at both pH, while poly(acrylic acid) at pH 10.2 and poly(vinyl pyrrolidone) at both pH take tails or loops segments on untreated TiO2.