Study On The Micellization And Gelation Behaviour Of PEO-PPO-PEO Aqueous Solution

Dissipative particle dynamics simulation method and experimental techniques,such as rheology and small angle x-ray scattering (SAXS), were used to study themicellization and gelation behavior of PEO-PPO-PEO (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)) aqueous solution, in which those propertieswere studied, such that the mechanism of the micellization and gelation behavior ofPEO-PPO-PEO aqueous solution, the effect of the length of hydrophilic PEO block onthe micellization and gelation behavior of PEO-PPO-PEO aqueous solution, and theeffect of the addition of17R4(PO14-EO24-PO14) to PEO-PPO-PEO aqueous solution onthe gelation behavior and gel structure transition.The main content are as follows:We study the micellization and gelation behavior of triblock copolymerpoly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in solution by bothDissipative particle dynamics (DPD) simulation method and experimental technics. Thecritical micellization concentration and the critical gelation concentration were obtainedfor the system at298K. The shape of the micelles was spherical as the concentrationwas below40wt%, which is in accordance with experimental results. Furthermore, theeffect of the length of PEO block on micelle shape and gelation behavior was studied.For block copolymer with short length of PEO block, the prolate ellipsoid micellesformed more easily. For Pluronics with similar hydrophobic PPO block length, when thePEO block became shorter, the micelle aggregation number became bigger, and thus thePEO chains in the micelle coronal became denser, so that the micelles were “harder”;otherwise, when the PEO block became longer, the micelles became “softer”. Thus,Thus, for the harder micelles, the critical gelation concentration decreased withincreasing length of PEO block. However, when the length of PEO block was quite long,the softer micelles were formed. Although the network structure is formed throughpercolation, the mechanical property of the formed network is almost invisible. Onlywhen the concentration increased to a very high value, the network showed highmechanical property, and thus the critical concentration when hard gel formedincreased.The reverse block copolymer PPO-PEO-PPO was introduced into PEO-PPO-PEOaqueous solutions, the micellization and gelation behavior of the system was complex.The reverse block copolymer17R4was added to the Pluronics EO20-PO70-EO20(P123),EO100-PO65-EO100(F127), and EO133-PO50-EO133(F108) aqueous solutions withdifferent molar ratios. The rheological properties of the different mixtures weremeasured to study the additive effect on the gelation behavior. The sol-gel transitiontemperature of the P123, F127and F108solutions shifted to a higher temperature whenadding17R4to the solutions. In addition, the existence of17R4greatly affected thestability of the gels. These results may help us better understand the gelation ofPluronics aqueous solutions.Rheology and small angle x-ray scattering (SAXS) were used to study the effect ofthe content of17R4and temperature on the gel structure of the17R4/F127mixedsolutions. It was indicated that the structures of sol, soft gel and hard gel werecorresponding to disorder phase, disorder/cubic coexisting phase and cubic phase. Withincreasing temperature, hard sphere radius and aggregation number of micelle decreased.For pure17R4, it is difficult to form micelles. However, when the temperature wasincreased,17R4chains took part in the formation of micelles and therefore the numberof micelles increased, which made the number of F127chains in one micelle decrease.Thus, the number of PEO blocks of F127in coronal part decreased and then the coronalpart became softer. As a result, a FCC(face center cubic)-BCC(body center cubic)transition occurred in the system with17R4/F127molar ratio of2:1.