Orientation Correlation and Dielectric Relaxation of the Zwitterionic Head Groups of Dimyristoyl‐Lecithin Multi‐Bilayer Vesicles

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Abstract
The spectrum of the complex permittivity of a colloidal aqueous dimyristoyl‐lecithin solution has been measured as a function of time. The change in the dielectric properties of bilayers was observed during the growth of the vesicles (after first small aggregates had been produced by sonication). The measurements were performed in the spectral range from 100 kHz to 40 MHz by fast response time domain spectroscopy. The data are phenomenologically treated in terms of a Debye relaxation spectral function and are also discussed on the basis of a theoretical model of the solutions. — The study supports the conception of a domain structure of the bilayer surface. It is shown, that the dielectric domains, which are characterized by a pronounced orientation correlation of the zwitterions, increase in size if the radius of curvature of the bilayers increases. There is also a strong relation between the dielectric relaxation time and the orientation correlation of the head groups. This result indicates that the reorientation of the zwitterions is a collective phenomenon. With respect to the kinetics of the process of vesicle growth, the data show a particularly high rate of increase in the vesicle size near the crystalline/liquid‐crystalline phase transition temperature of the bilayer system.