Studies of Constrained Dynamics of the Phase Transition in the Artificial Bilayer Membrane of Dialkyl Ammonium Amphiphile by Quasielastic Neutron Scattering

Quasielastic neutron scattering studies on the gel to liquid crystalline phase transition of the synthetic bimolecular membrane made of didodecyl dimethyl ammonium bromide (DDAB) dispersed in D2O were performed to reveal that the behavior of the proton motion of the alkyl chain changed drastically through the transition temperature. Below the transition temperature of 16.5°C, the predominant motion of protons is the vibrational one in the well defined potential well, whereas above the transition at T=20°C, superimposed upon the increased vibrational motion, protons can jump the average distance of the order of 0.5 Å in every 6 to 7 picosecond around the chain axis. Such observation and the presumed important role of the kink formation process attributed to the membrane transition are discussed from the view point of the constrained dynamical system.