INTERACTIONS BETWEEN COVALENTLY CROSS-LINKED ETHYL(HYDROXYETHYL)CELLULOSE AND SDS

The equilibrium swelling of chemically crosslinked gels based on ethyl (hydroxyethyl) cellulose (EHEC) in aqueous solutions of sodium dodecyl sulphate (SDS) was studied as a function of the SDS concentration at various temperatures and salt concentrations. Comparisons were made wi th gels based on poly-N-isopropylacrylamide (p-NIPA). Both polymers ar e known to form complexes with SDS above a critical association concen tration (cac) of the surfactant, and both display a lower critical sol ution temperature (LCST) in water. For both types of gels, an increase in the equilibrium gel volume was seen with increasing SDS concentrat ion above the cac, up to a maximum value when the SDS concentration in the external solution reached the critical micelle concentration (cmc ). Above the cmc, the equilibrium gel volume decreased slowly with inc reasing SDS concentration. A volume collapse of the EHEC gels was obse rved in a temperature interval around the LCST of EHEC in solution. Ab ove the cac, the collapse transition moved monotonically towards highe r temperatures with added SDS. At lower SDS concentrations, however, t he opposite trend was found. The swelling of the gel was less in the p resence of salt and SDS, and a pronounced minimum in swelling appeared with added SDS when the salt concentration was sufficiently high (ca. 10 mmoles/l). Under these salt conditions, the LCST of the linear EHE C also passes through a deep minimum (below room temperature) on addit ion of SDS. (C) 1997 Elsevier Science Limited.