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 relationship was found between viscosity and temperature, with curve slopes dependant upon poloxamer concentration. The viscosity of 25% poloxamer 407 aqueous solution showed a Newtonian fluid at 4 degrees C and linearly 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 closer approach of polymer chains, which gave rise to an increase in the number of interactions among the chains, gave an increase in the solution viscosity with temperature. The gelling concentration was examined using an interfacial tensiometer. The results showed that the first inflection point appeared at the 0.003% (w/w) concentration and the second point appeared at the 17.5% (w/w) concentration. It implied that poloxamer solutions formed monomolecular micelles at low concentration; as the concentration was increased, multimolecular aggregates were formed.