CALCULATION OF SURFACE POLARITY PROFILES FROM THE EXPERIMENTAL HYDRATION FORCE DATA

A method for the evaluation of the interfacial polarity profiles is in troduced based on a previously proposed model (ref 10). This numerical procedure depends on the knowledge of a few, reasonably well-known bu lk solvent properties-such as the static and high-frequency dielectric constant. Water correlation decay length is argued to affect the resu lts of the data analysis only little as long as its value is sufficien tly smaller than the effective width of the interfacial region. The co rresponding analysis of the hydration force data for the phospholipid bilayers shows that the interfacial polarity profile for such systems can be approximated well by a simple exponential function. The latter is uniquely defined in the region covered by the experimental data. Ho wever, without additional assumptions no extrapolations in the experim entally unexplored region are possible. In order to learn more about t he molecular mechanism and the range of the surface hydration, as well as about the hydration-induced changes in the interfacial structure, more and more detailed experimental hydration force data should be col lected.