Swelling in organic-inorganic multilayer systems

We have investigated the swelling of organic-inorganic structures based on fluorocarbon polymer (CF2) layers sandwiched by two layers of inorganic ionic (HfO2) and inorganic covalent ~CdS! materials. The swelling of the CF2 layer produces cracks on the uppermost inorganic layer. The cracks form a network of hexagonal defects with random distribution. The extension of the pattern and the mean unit size have been measured for different solvents by using a purposely developed optical profilometer. We show that the swelling phenomenon strongly depends on the polar forces between the molecules of the solvent and those of the inorganic layers. The electric dipole moment of the solvents and the ionicity of the inorganic materials are thus the crucial parameters influencing the crack density and shape.