In some cases a coating can “swell” when molecules of a solvent
are introduced in between the polymer chains, or voids or microcracks
in the coating are filled with electrolyte, small parts of the
coating are dissolved, etc. (Fig. 5). All these possibilities have in
common that the coating becomes heterogeneous in nature with
a varying capacitance and resistance throughout the layer. This
response is rarely applicable for beverages and food, but may be
encountered for products with many organic solvents, like paints.
It is also observed when a coating is undercured or overcured.