A liquid film of thickness less than 100 nm with soluble surfactant is subject to disjoining pressure or conjoining pressure induced by intermolecular forces

which determines its stability and wettability.In the present paper

based on three nonlinear partial differential evolution equations for film thickness

surfactant interfacial concentration and bulk concentration derived from the lubrication theory

the processes of droplet spreading driven by surfactant under the action of intermolecular forces in positive and negative systems were simulated numerically

and the effect of intermolecular forces

collectively called disjoining pressure or conjoining pressure

was analyzed.Disjoining pressure promoted droplet spreading stably and inhibited film dewetting occurrence in a positive system; disjoining pressure played a destabilizing role in a negative system by amplifying perturbations

and changing the effect of Marangoni stress.The droplet in a positive system presented unstable evolution characteristics under conjoining pressure

which led to film rupture ultimately; in a similar effect with disjoining pressure

conjoining pressure further enhanced the instability of droplet evolution in a negative system.