ABSTRACT
Wetting is governed by molecular interactions in the outermost surface layer of a few angstroms. Consequently, the forces dictating the wetting behavior of organic substances do not originate from the organic molecule as a whole, but rather from the outermost surface groups. Furthermore, for interfacial-energy minimization reasons, the molecules tend to arrange themselves in the surface layer in such a
way that only their low-energy or high-energy portions come into contact with the surrounding phase. As a result, the wettability of an organic material is not related to its overall chemical structure, but depends on the chemical nature of energetically favored functional groups and on the extent to which these are exposed at the material surface. Langmuir [1-3] first developed this basic concept in his studies of the pure liquids of small molecules. More recently, it became apparent that the above considerations are equally applicable to long chain molecules (i.e. organic polymers) [4-6]. It is now widely accepted that the extent of the selective surface exposure of functional groups in polymers, unlike that in their low-molecularweight analogues, must be largely controlled by the conformational characteristics of the molecular chains; however, very little work has been done to explore this statement [7-11]. Furthermore, since most of the fundamental research on the molecular mechanisms of wetting has been carried out with the surfaces of organic polymers, progress towards a molecular-based description of wetting phenomena has been hampered by the lack of microstructural understanding of the surfaces. In this paper, we report on the results of systematic experimental studies of the correlation between the molecular structure (as characterized by the stereochemistry and conformations of macromolecules), the extent of the selective surface exposure of functional groups, and the wettability of polymer surfaces.
