The gel-liquid crystal phase transition has been studied by the temperature and frequency dependent dielectric relaxation behavior of liposomes in an aqueous solution (40 g L(-1) DPPC-water mixture). Four relaxation processes were observed in the frequency range from 40 Hz to 30 GHz which were ascribed to different molecular mechanisms, related to the structural units of the system. The gel-liquid crystal phase transition was also described very accurately from the temperature-dependent dielectric relaxation strength, relaxation time and symmetric shape parameter of the relaxation functions obtained from the fitting procedure. Relaxation process 3, obtained from the dielectric fitting procedure, was confirmed by dielectric modulus analysis. A comparison of the lipid membrane with non-biological systems like liquid crystals was performed. It was determined that the lipid membrane has a ferroelectric liquid crystal like behavior. Process 3 is comparable to the soft mode relaxation process observed in ferroelectric liquid crystals which was detected close to the smectic-C*-smectic-A phase transition. Differential scanning calorimetry was also used to confirm the gel-liquid crystal phase transition of this mixture.

The dynamic light scattering (DLS) has been used to investigate the diffusion behavior and the size distribution of liposome. DLS experiments show two classes of particles with their hydrodynamic radii being 4-12 nm and 66-80 nm. The numbers of particles associated with the two peaks are estimated by means of the scattering properties of the particles.Broadband dielectric spectroscopy (BDS) has been used to investigate the dynamical structure of liposome in aqueous solution of water, which makes it possible to precisely explain the molecular mechanism, structures and various properties as a function of temperature and frequency. We have observed four relaxation processes, where two low frequency processes are commonly observed in charged macromolecules in aqueous solution, third process appeared in the MHz region due to the motion of ions, which is also related to the molecular motion of the lipid, and the high frequency process appeared about 20 GHz is due to free water surrounding liposome. Gel-LC phase transition has been described very accurately from the temperaturedependent shape parameter, β, obtained from the Cole-Cole fitting. The β value in LC phase is smaller than that in gel phase.

We performed dielectric relaxation measurements for 5CB/benzene mixtures in the frozen state at frequencies from 40Hz to 1 OGHz and for liposome/water dispersion systems at frequencies from 300MHz to 20GHz. When 5CB/benzene mixtures take Nematic (N) phase from Isotropic (I so) phase with increasing concentration, the relaxation time distribution parameter, ~. becomes smaller. On the other hand, gelliquid crystal (LC) phase transition for liposome/water system is characterized by a change in the parameter ~ . The ~ value in the LC phase is smaller than that in the gel phase. It is considered that the larger fluctuation of water molecules is realized by interaction between water and lipid molecules in the LC phase with higher mobility. Therefore, dynamical behaviors of LC and liposome in the LC phase are reflected by smaller ~ values with respective molecular mechanisms.