title: Dynamic and static properties of the concentrated micellar solution and gel phase of a triblock copolymer in water.
abstract: The dynamic and static behavior of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer "P94" is studied in aqueous solution. This polymer forms transparent micellar phase structures through the whole phase diagram. The characteristics of these structures can be tuned by variation of temperature and concentration. The transparent gel at high concentrations and at ambient temperatures is the main interest in this study. The transition from the ergodic solution to this nonergodic gel or glass state can be reached in two ways: at constant temperature with an increase of concentration or at constant concentration with increasing temperature. We characterize the system in both ways with dynamic and static light scattering and with small-angle x-ray scattering experiments. At 40 degrees C, no concentration dependent change in the micellar structure of the system can be detected from the small-angle x-ray scattering results. Even in the gel we find globular particles. This is important for the evaluation and interpretation of the dynamic light scattering measurements. In the ergodic phase region at constant temperature, we find that a ratio of 2.17 gives a perfect fit to the experimental data when we allow the effective volume fraction to be proportional to the mass fraction. In the gel region we find two diffusional decays in the intensity correlation functions and an arrested part. The diffusion coefficients from the faster decay stay constant inside the gel and the nonergodicity parameter increases linearly with concentration. Both, the fast and slow diffusional modes show no angular dependence of their scattering intensities, indicating their origin from small objects, while the arrested mode comes, as expected, from structures larger than the resolution of the experiments.
authors.affiliation: Institut für Chemie, Karl-Franzens-Universität, Graz, Austria.
authors.forename: Helmut
authors.initials: H
authors.lastname: Lindner
authors.forename: Günther
authors.initials: G
authors.lastname: Scherf
authors.forename: Otto
authors.initials: O
authors.lastname: Glatter