Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 7: POSTERS Rheology
CPP 7.24: Poster
Montag, 25. Februar 2008, 16:45–19:00, Poster A
Supercooled Water Confined in Reverse Micelles - A Neutron Scattering Study — •Tinka Spehr1,2, Bernhard Frick2, Isabelle Grillo2, and Bernd Stühn1 — 1TU Darmstadt, Deutschland — 2Institut Laue Langevin, Grenoble, Frankreich
Water, the surfactant AOT and oil (toluene or decane) form a stable droplet phase microemulsion over a wide range of compositions. Spherical water droplets surrounded by a mono-layer of AOT are dispersed in oil. The size of the water pool can be varied by changing the molar ratio ω of water to surfactant: radii between a few Å and several nm can be obtained, which makes the droplets an attractive model system for the study of soft confined water. We used neutron time-of-flight (TOF), backscattering (BS) and small angle scattering (SANS) to study the system with a fixed droplet volume fraction φ =0.2 and ω ranging from 3 to 40. The phase behaviour of the microemulsion was investigated by SANS from 290 to 220 K. The droplet structure is stable down to temperatures T much below the freezing point of bulk water. The smaller the droplets (the smaller ω) the lower T down to which the droplet size is maintained. When reducing T below this phase transition the droplet size shrinks. Freezing of the confined water was observed by BS: the freezing temperature as a function of droplet size follows the same dependence as the phase transition temperature monitored[1]. Inelastic measurements (TOF, BS) show that the supercooled confined water is strongly slowed down compared to bulk water. Rotational and translational dynamics of the water are discussed.
[1]T Spehr, B Frick, I Grillo, B Stühn (2007), accepted by JPCM