Characterization of a PEO-PPO-PEO block copolymer system
The investigated EO27-PO39-EO27 triblock copolymer, Pluronics P-85, is a nonionic surface-active agent which has a monomeric molecular weight of 4600, of which 500% corresponds to the PEO component. P-85 exist in complex states of aggregation in aqueous solution. Monomers, micelles and larger aggregates (clusters) coexist at lower concentrations in relative proportions which depend on temperature. The micelles are composed of a core of the water-insoluble PPO-block with a swollen shell of PEO-endblocks, having a hydrodynamic radius of 75 Å. The monomers have a hydrodynamic radius of 18 Å. At higher temperatures and concentrations, the micelles are close-packed in a body-cente-red-cubic (b.c.c.) liquid crystalline phase which is solid-like and glass-clear. At even higher temperatures this gel of micelles “dissolves” again. For structural (internal) information on the monomer, the micelle, and to study the interacting micelles and the gel, small-angle x-ray-scattering measurements and dynamic light-scattering measurements have been made in the concentration range 1 to 25% (w/w) with the temperature range 5 to 70°C. The micellization was detected clearly by ultrasound velocimetry measurements. To characterize the viscosity of the gel (cubic phase) advanced densimetry was performed.
Key wordsTriblock copolymer micelle gel small-angle x-ray scattering ultra-sound velocimetry densimetry
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