Abstract

Classical density functional theory is used to study the general aspects of wetting phenomena occurring in nonpolar neutral molecule system near a flat solid wall. Current cognitions of the wetting behavior are looked at, validated, corrected and extended. Several new observations are made: (i) the present theoretical calculations suggest that over a broad range of the surface potential parameters the pre-wetting transition temperature interval significantly reduces with the wetting temperature, and at the same time a continuous and monotonous increase of the wetting temperature is induced by decreasing the surface potential range and/or relative strength of surface atom versus fluid atom interaction. (ii) There exist lower limit values of both the surface potential range and the relative strength, below which the wetting transition is impossible. (iv) The present theoretical calculations confirm an experimentally found no adsorption occurring in weak surface potential substrates all the way to the relevant critical temperature by showing the impossibility of wetting at bulk critical temperature and its surroundings; moreover, the calculations extend the experimental observation to a wider parameter domain by indicating that the impossibility is not only unique feature of the weak surface potential substrates, but also applies to all situations of the surface potential range and relative strength. (v) With progressive increase of the relative strength and/or progressive decrease of the temperature, the interfacial phase behavior becomes increasingly complex: the (pre-)wetting transition and layering transition (which can be thermodynamically stable, metastable or even situated at supersaturated vapor phase) are intertwined closely; this challenges the popular knowledge that there is no (pre-)wetting for strong substrates for which the pre-wetting is replaced by the layering transitions.

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