The Association of Water on Molecular Layers

Abstract

AbstractHydrocomplexes which form around the hydrophilic group of surface‐active compounds are one of the basic requirements for the colloid‐chemical behaviour of these compounds. According to our conception, the complex in which four water molecules are attached to the hydrophilic group is in equilibrium with the one‐water‐molecule‐complex while compressing a myristic acid monolayer by a Langmuir‐balance. The space requirements of these complexes can be calculated from the size of the hydrophilic group and from the space requirement of the water molecules, which amount to 7.3 Å2 for each one. Polymeric substances follow the same laws, as will be demonstrated by the example of polydimethyl‐siloxane.Depending on the surface area available, a discrete number of water molecules per (CH3)2SiO unit attach themselves to polydimethylsiloxane spread upon water. When such films are compressed, four defined states of orientation will result.This concept is transferred to surfaces of solids. It is shown that when silicone‐treated glass plates are sprayed with water, four defined states of wetting will form which are to be co‐ordinated with the states of orientation.Glass plates with these different states of silicone coating are prepared; they are subjected to measurement of contact angles which they form with various fluids. Informative relationships of adhesion energy, surface tension on solids, wettability, etc. to the interfacial coating are shown when the surface tension of the fluid is plotted versus the adhesion energy.Pronounced polarization of the molecules within the complexes is found while they are adsorbed on the interface of the solid.The heat of association, which is the same whether the poly‐dimethylsiloxane films are adsorbed on water or glass, is calculated from the adhesion energy. Finally, the heat of association allows conclusions to be drawn as to the tensile strength of silicone rubber.