THERMORHEOLOGIC PROPERTIES OF AQUEOUS-SOLUTIONS AND GELS OF POLOXAMER-407

A rheological study of poloxamer 407 aqueous solution of 10-25% (w/w) concentrations was carried out at temperatures ranging from 27 degrees C to 45 degrees C and at various shear rates. An exponential relation ship was found between viscosity and temperature, with curve slopes de pendant upon poloxamer concentration. The viscosity of 25% poloxamer 4 07 aqueous solution showed a Newtonian fluid at 4 degrees C and linear ly increased on increasing temperature. The viscosity of 25% poloxamer 407 aqueous solution was sharply increased at about 12 degrees C and maintained highly constant. During such a desolvation process, the clo ser approach of polymer chains, which gave rise to an increase in the number of interactions among the chains, gave an increase in the solut ion viscosity with temperature. The gelling concentration was examined using an interfacial tensiometer. The results showed that the first i nflection point appeared at the 0.003% (w/w) concentration and the sec ond point appeared at the 17.5% (w/w) concentration. It implied that p oloxamer solutions formed monomolecular micelles at low concentration; as the concentration was increased, multimolecular aggregates were fo rmed.