Gelation behavior and mechanism of binary Pluronic block copolymers

Gelation behavior of binary Pluronic block copolymers of F127/F68 was evaluated by rheological measurements.The results showed that when the total copolymer mass fraction was fixed at 20%，the gel transition temperature increased from 20.8 °C to 38.5 °C and the elasticity modulus decreased 83.5% with the weight ratio of F127/F68 from 10∶0 to 8∶2.The formed gel was typical of shear thinning property.Nevertheless，according to DSC analysis,the critical micelle temperature hardly changed with the composition of the mixture,and the gelation process was thermo-reversible and no endothermic peak was detected at the gel transition tempe-rature.The hydrophilic “corona” of the micelle was studied using viscometry.The results showed that the shell hydration of the micelle decreased while increasing the ratio of F68.Particle size analysis found that the micelle was slightly smaller as the proportion of F68 in the mixture was increased.The diagram exhibited the transition process of the binary system from micelle to gel.Increased the ratio of F127，more micelles would be involved in the formation of gel.And raised the temperature，the repulsive interactions among close-packed spherical micelles became stronger.Both of them could help to increase the micellar volume fraction,which could benifit to the gel formation.