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CP: Chemische Physik

CP 17: Postersitzung Transportprozesse durch Grenzflächen und Membranen

CP 17.4: Poster

Tuesday, March 18, 1997, 18:30–21:15, FBH

A Liquid/Frozen Transition of a Statistical Copolymer Anchored at the Air/Water Interface — •Heiko Ahrens¹, Klaus Lowack¹, Jürgen Krägel², and Christiane A. Helm³ — ¹Institut für Physikalische Chemie, Johannes Gutenberg-Universität, 55099 Mainz — ²Universität Potsdam, c/o MPI für Kolloid- und Grenzflächenforschung,12489 Berlin — ³Fachrichtung Kristallographie, Universität des Saarlandes, 66041 Saarbrücken

At the air/water interface a monolayer of random poly(methacrylate) copolymer with a hydrophobic and a hydrophylic substituent exhibits a transition from the fluid to a frozen state, which can be induced by lateral compression. Various hydrophobic stubstituents were tried. Above this transition any amphiphilic molecules mixed with the monolayer are immobile. The phase transition could be clearly observed with rheological experiments, in the fluid phase the increase of the viscosity by 3.5 decades could be described with the free area model. With small angle X-ray reflection, the electron density profile of the monolayer is investigated. In the frozen phase, the center of the water adjacent head groups (dioxale rings) are further away from the hydrocarbon part than in the fluid phase, suggesting of a pronounced conformational change of the head groups and/or the polymer chain at the phase transition. This conformational change hinders the diffusion of guest molecules within the monolayer.