INTERACTIONS OF POLYMERS AND CATIONIC SURFACTANTS WITH THIOCYANATE AS COUNTERIONS

The interactions of deodecylammonium ions with nonionic polymers such as polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyvinylalcohol-acetate copolymer (PVA-Ac) were strengthened by changing the counterion from chloride to thioeyanate. For example, whereas the specific viscosity of a PVP solution underwent little change by addition of dodecylammonium chloride, addition of dodecylammonium thiocyanate (DASCN) decreased it at low concentrations and raised it remarkably at high concentrations. Such a viscosity change by DASCN is of a different type from that by sodium dodecylsulfate (NaDS) and may be attributed to a concurrent binding of the dodecylammonium ion with SCN- to the hydrophobic parts of the polymers. Therefore, the mechanism of binding of DASCN to the polymers is different from that of NaDS, whose dodecylsulfate ion is itself bound directly to many nonionie polymers. The binding of DASCN to the polymers was also exhibited by the higher solubilization power of the mixed solutions of DASCN wih the polymers than that of the DASCN solution alone for an oil-soluble dye Yellow OB. The binding of the dodecylammonium cation to PVP with the aid of the inorganic counterion was in the order of SCN- > I- > Br- > CI-, and as for small organic anions such as ethylsulfate, butyrate, and caproate the effect was very poor or insignificant. Dodeeylpyridinium thiocyanate did not show an interaction with PVP and PEO, but interacted strongly with hydrophobie PVA-Ac. The polymer-cationic interaction in the presence of thiocyanate ion thus depends specifically on the polymer and cationic head group of the surfactant. © 1997 Elsevier Science Ltd. All rights reserved.