# Water and Thermal Diffusivity in a Lipid-Water Smectic Phase

 Title: Water and Thermal Diffusivity in a Lipid-Water Smectic Phase Author: Pershan, Peter S.; Chan, Winston K. Note: Order does not necessarily reflect citation order of authors. Citation: Chan, Winston K., and Peter S. Pershan. 1978. Water and thermal diffusivity in a lipid-water smectic phase. Biophysical Journal 23(3): 427-449. Access Status: Full text of the requested work is not available in DASH at this time (“dark deposit”). For more information on dark deposits, see our FAQ. Full Text & Related Files: Chan_Water.pdf (2.198Mb; PDF) Abstract: We report the first application of light scattering to measurement of the hydrodynamic relaxation of inhomogeneities in water concentration within a multilamellar, or smectic A, phospholipid water system (dipalmitoyl) phosphatidyl choline). Although the relaxation process in the multilamellar phase is different from the diffusion process in liquid phases, the relaxation rate can be described in terms of a diffusion coefficient. For diffusion parallel to the lamellae, diffusion coefficients ranging from $$8 \times 10^{-7}$$ to $$2 \times 10^{-5} cm^2/s$$ were measured over a range of temperature and water concentrations. We describe a model that expresses the diffusion coefficient in terms of the chemical potential for water inside the multilamellar phase and the effective thickness of a "free water zone." The deduced thickness of this free water zone is in good agreement with estimates from X-ray diffraction results. The activation energy for the diffusion process is also deduced from the data, and is found to decrease monotonically with increasing water concentration. We also found the thermal diffusivity to be about $$10^{-3} cm^2/s$$ with only a weak temperature and water concentration dependence. The experimental technique is a new version of forced Rayleigh scattering. The method uses the phase information of the scattered light to improve the ability to detect weak signals. Experimental details are reported. Published Version: doi:10.1016/S0006-3495(78)85460-5 Other Sources: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1473527/pdf/biophysj00743-0102.pdf Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10361970 Downloads of this work: