Conductive aqueous layer formation at the gel-substrate interface in equilibrium with 100% RH environment

The paper describes results of theoretical modeling and experimental verification of conditions leading to the formation of a conductive aqueous layer at the interface between gels and substrates at 100% RH or equivalent (water immersed) conditions. Thermodynamic analysis of clean surfaces and interfaces shows that displacement of the interface between gels and inorganic substrates (e.g., ceramics and integrated circuits) by water is thermodynamically favorable while gel-organic substrate interfaces are stable versus such displacement. The presence of a water-soluble contaminant on the substrate will cause formation of water droplets whose diameter can be determined from the balancing of the osmotic and interfacial tension effects. If the total surface coverage by droplets (which is independent of the contaminant particle size distribution) exceeds the critical two-dimensional (2-D) percolation threshold, a continuous path of electrical conductivity is formed. For sodium chloride contaminant the critical surface concentration leading to such event was calculated and shown experimentally to be 10/sup -7/ g/cm/sup 2/. Inorganic filler in the gel in the amount exceeding the three-dimensional (3-D) percolation limit can cause bulk conductivity of the gel material at high humidity due to formation of an aqueous layer at the gel-filler interface.