THE RIPPLE PHASE IN A DMPC WATER MIXTURE - A DIELECTRIC INVESTIGATION

The dielectric behaviour of a DMPC-water mixture has been investigated in the frequency range from 1 kHz to 10 MHz and in the temperature interval from 0 to 40°C over the crystalline-liquid crystalline phase transition temperatures. A model to explain the dielectric characteristics of the DMPC-water mixture as a function of frequency, and in general for each DPL-water mixture which displays a ripple phase, is proposed. The model is based on the assumption that a particular contribution to the total polarizability comes from the ripple deformation of the bilayer. This contribution is evaluated supposing strong interactions between the lipid head groups with the formation of in-phase domains of correlated electric dipoles. A further assumption relates the extension of the domains to a set of spatial modes, called ripplons, thermally activated in the ripple phase. By the ripplon dispersion relation, the dipole domain extensions (hence the polarizability), were made frequency dependent. The final result shows that the anomalous peak which appears in the permittivity at the ripple phase temperature interval is qualitatively well fitted by our model. © 1990 Taylor & Francis Group, LLC.