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ABSTRACT:The effects of alcohol addition on gelation and micellization in aqueous solution of EO100PO65EO100 (Pluronic F127) triblock copolymer were studied using tube inversion method (TIM), rheometry, dynamic light scattering (DLS), and high sensitive differential scanning calorimetry (DSC). Upon the addition of alcohol such as methanol or ethanol, the hard gel transition temperature is raised resulting in reduced hard gel region in the phase diagram and these alcohols were shown to increase the critical micelle temperature (cmt). Butanol, however, clearly lowers hard gel transition temperature and cmt. In the case ofpropanol up to 15 v% the onset temperature of the hard gel is slightly lowered while the hard gel transition temperature is raised for propanol content more than 20 v%. The experimental investigation shows that lower alcohols such as methanol and ethanol prevent the onset of gelation and micellization while higher alcohols such as butanol favor gelation as well as the formation of micelles in aqueous solution ofEO100PO65EO100 triblock copolymer.KEY WORDS Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) Triblock Copolymer I Alcohol Effect/ Hard Gel Transition/ Micellization / Numerous studies have been devoted to aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly-(ethylene oxide) (PEO-PPO-PEO) triblock copolymers using experimental techniques such as small angle neutron scattering (SANS), 1 -5 small angle X-Ray scattering (SAXS), 6 · 7 fluorescence, 8 · 9 differential scanning calorimetry,10, 11 static and dynamic light scattering, 12 · 13 and rheological measurement. 10 · 14 · 15 These copolymers are commercially available as surfactants (Pluronics®; BASF or Poloxamers®; ICI) and widely used for emulsification, detergency, dispersion stabilization and so forth. 16 Because of the amphiphilic character of the PEO-PPO-PEO triblock copolymer, it forms spherical micelles 6 · 17 due to its self-assembling nature in aqueous solution when its solution concentration exceeds the critical micelle concentration (cmc) 8 · 14 · 18 or solution temperature is increased above the critical micelle temperature (cmt) _5,8,18 In aqueous solutions of E0100P065E0100 (Pluronic F127) sol-to-gel and gel-to-sol transition is observed as temperature is increased at copolymer concentrations as low as 20 wt%. 6 · 15 · 18 · 19 Gels formed with this triblock copolymer are physical gels formed through non-covalent associations and gels reversibly transform to sols when the temperature is lowered below the gelation temperature namely thermoreversible gelation. 15 · 18Several mechanisms of thermally reversible gelation of the E0100P065E0100 copolymer solution have been proposed. The sol-to-gel transition has been explained in terms of intrinsic change in micellar properties 20 or entropic change associated with locally ordered water molecules close to the PPO hydrophobic blocks. 21 SANS experiments showed that the gel transition is due to hard-sphere crystallization when the micelle concentration...

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Mesoporous organosilicas based on a bridged organosilicate have been synthesized using a triblock PEO-PLGA-PEO copolymer containing more hydrophobic poly(DL-lactic acid-coglycolic acid) block and the structural difference between mesoporous organosilicas prepared from PEO-PLGA-PEO and PEO-PPO-PEO block templates is discussed.