AFM Studies on the Effect of Crystalline Interphase on Adhesion of Polyurethane Thin Film to Al Substrate

Polyurethanes crystallized at the aluminum surface, but the crystalline interphase varied with polyol OH number. Early stage of spherulite formation was characterized using AFM after removing amorphous polyurethane. The crystallite shapes of polyurethanes were correlated with the bond strength measured from indentation debonding. Interestingly, the samples involving non-specific shape of crystallites displayed high bond strength, while the polyurethanes with rod-like crystallite poorly adhered to aluminum substrate. Although crystallite shape did not unequivocally relate to bond strength, the results propose that there is a probable correlation.