RHEOLOGICAL BEHAVIOR OF POLOXAMER 407 AQUEOUS-SOLUTIONS DURING SOL-GEL AND DEHYDRATION PROCESSES

A theological study of 25% poloxamer 407 aqueous solutions was underta ken during sol-gel and dehydration processes. Upon the sol-gel transit ion, the solution changed from a Newtonian to non-Newtonian fluid thro ugh the mechanism of desolvation. During such a desolvation process, t he closer approach of polymer chains, which gave rise to an increase i n the number of interactions among the chains, was reflected by an inc rease in solution viscosity with temperature, In this study, three tem perature regions, namely, the unimer, transition, and micelle regions originally derived from the light scattering technique, were also demo nstrated. The boundary temperatures were 10 degrees C between the unim er and transition regions and 18 degrees C between the transition and micelle regions. Once the gel had been formed above the boundary tempe rature 18 degrees C, the indices K and n remaining nearly constant, th e gel structure was thought to remain unaltered with temperature until an excessively high temperature caused the destruction of the gel str ucture. At room temperature, the gel underwent a process of dehydratio n, the evaporation of water from the surface layer occurring first, an d eventually dried to a solid. It was found that polyoxyethylene cryst als precipitated in the gel during dehydration.