Wetting Dynamics of an Oil-accommodating Adhesive

Abstract Oil-accommodating adhesives are widely used industrially to avoid the necessity of degreasing metals before bonding. We have undertaken a study of the behaviour of drops of an uncured model epoxy adhesive on both degreased and oiled, galvanized, steel sheet during temperature increase. Contact angle, θ, vs. time, t, behaviour is significantly different for the two cases. On a degreased substrate, wetting rate initially increases with temperature, therefore time, due to decreasing viscosity, and then becomes reduced as equilibrium is approached. For oiled substrates, there is a central pseudo-plateau in the θ vs. t curve, corresponding to a modified capillary balance, itself caused by significant absorption of the oil by the adhesive. This behaviour is modelled semi-quantitatively. In the case of spreading on a degreased substrate, a simplified model is proposed to explain dynamic effects related to reduced viscosity during temperature rise.