Abstract
Ultrasonic spectra (2×105Hz to 2×109 Hz) and complex dielectric spectra (104 Hz to 4×1010 Hz) are reported for aqueous solutions of vesicles from lipid mixtures near their main phase transition temperature Tm. The results are compared to such for 1,2-dimyristoyl-L-3-phosphatidylcholine systems. Various relaxation terms are identified. One term results from the domain structure fluctuations of the membranes. It features critical point characteristics. Another term is due to the axial diffusion of the lipid molecules within the membrane. It also reveals substantial effects of slowing near Tm. Relaxation times reflecting the zwitterionic head group reorientational motions and the alkyl chain structural isomerisation display step like changes at the phase transition. An additional relaxation term exists close to Tm only. It is assumed to indicate small-area deformations of the vesicles.
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