Polymer coatings containing aligned mica flakes can reduce solute permeability by more than an order of magnitude. This permeability reduction can be used to inhibit corrosion of aluminum coupons coated with mica-filled epoxy. The extent of permeability reduction, which depends on the flakes' volume fraction, shape, and alignment, varies with volume fraction squared, as predicted by some published theories. The flake alignment can be achieved either by solvent evaporation or shear, but is independent of the shear rate used to orient the flakes. This shear rate independence is consistent with fluid mechanics calculations, though these same calculations predict better flake alignment than is found by small-angle X-ray diffraction.
Bibliographical noteFunding Information:
Dr. Francis Guillaume helped us with the coupon preparation for corrosion studies. This work was primarily supported by the US Air Force (AFOSR F49620-01-10333). Other support came from the Petroleum Research Fund of the American Chemical Society (grant 36528-AC9) and from the Department of Energy (grants DE-FG07-02ER63509 and CRADA LA01C10455).