Recent Thermodynamic Data on Vicinal Water and a Model for Their Interpretation*

Results of recent measurements on vicinal (i.e. surface modified) water are reported, particularly data for the density, thermal expansion coefficient, and viscosity. The results are discussed and related to previous studies, suggesting that vicinal water extends over large distances, probably in the range of 30 to 100 molecular diameters. It is proposed also that vicinal water is induced not only by proximity to a »solid« interface but may also occur as vicinal hydration of macromolecules larger than a certain minimum size, likely in the range of 1000 to 5000 Daltons. The temperatures (Tk) at which the thermal anomalies in the properties of vicinal water occur have been confirmed by an extensive DSC study. The critical temperatures are found to be independent of the chemical nature of the solid substrate, based on DSC measurements with porous quartz, polystyrene suspensions and diamond powder, thus lending credence to the reality of the »Paradoxical Effect«. Finally, a percolation model of vicinal water, based on the work by Stanley and Teixeira, is discussed. The model leads to a predicted value for the density of vicinal water of 0.97 g/cm3 in good agreement with the observed value. However the model does not predict the occurence of the thermal anomalies.