Rheological and Morphological Characterization of Triblock Copolymer (PEO-PPO-PEO)-Clay Gel in Aqueous Solution
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Rheological and Morphological Characterization of Triblock Copolymer (PEO-PPO-PEO)-Clay Gel in Aqueous Solution Jun Jiang, Chunhua Li, Miriam H. Rafailovich, Jonathan C. Sokolov Department of Material Science and Engineering, SUNY at Stony Brook Stony Brook, NY, 11794-2275 ABSTRACT Thermal gelation and structure properties of high concentration triblock copolymer poly (ethylene oxide)99-poly(propylene oxide)69-poly(ethylene oxide)99 (Pluronic F127)-clay aqueous solutions were characterized by rheological measurements and scanning electron microscopy (SEM). The sol-gel transition temperature, as well as the viscosity of the F127 solution was found to depend both on the concentration of polymer and clay filler. In all cases, Pluronic F127 gels are pseudoplastic, showing the shear-thinning behavior. Above the gel transition, the viscosity of the solutions increased with increasing the clay concentration. The corresponding macrostructure of the gels was studied by lyophilizing thick samples and scanning them with a scanning electron microscope (SEM). A well-ordered network of porosity was observed as a function of polymer concentration and orientation. INTRODUCTION Non-ionic amphiphilic triblock copolymer poly (ethylene oxide)x –poly (propylene oxide)y –poly (ethylene oxide)x (PEOx-PPOy-PEOx) has been studied for several decades. They are commercially available in a variety of lengths. Among all kinds of these polymers, pluronic F127 (PEO99-PPO69-PEO99) is most widely studied [1-3]. In general, the copolymer aqueous solution is in a unimer state at low temperatures and low polymer concentration since both blocks (PEO and PPO) are water-soluble at low temperatures. Increasing the temperature causes an increase in the hydrophobicity of the PPO block and leads to spherical micellar formation. The spherical micelle consists of a core of mainly the hydrophobic PPO blocks with a low water content surrounded by a water-swollen corona of PEO blocks [4, 5]. Since this kind of copolymer has thermal reversible property, they are widely used in various industrial and clinical applications, such as paints and coatings, laundry detergents, cosmetic products, and pharmaceutical formulations. The rheological and gelation properties of Pluronic polymer solution can be affected by the presence of various additives, such as solvent, salt and ionic surfactant [6, 7]. In the present study, we investigate the effect of clay particles on the morphological and rheological properties of this triblock copolymer hydrogel. EXPERIMENTAL DETAILS Pluronic F127 (12,600 Daltons, 70% w/w PEO) was obtained as gift from BASF (Mount
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Olive, NJ, USA). The de ionized water used was treated with Millipore-Q water purification system. Cloisite® Na+ (CNa) was purchased from Southern Clay Products Inc. Gels were prepared on a weight basis using the cold method. Concentrations of Pluronic polymer F127 and clay are expressed by weight percentage. Pluronic polymer was dissolved to deionized (DI) water and kept stirring at 4°C on a wei
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