Particles in polymers: surface chemistry of their nucleation, growth, configuration, and interactions with the matrix

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Abstract
The surface chemistry and thermodynamics of the nucleation, growth, configuration, and host–guest interactions of small particles within softenable substrates is investigated. It is found that novel subsurface particle monolayers form rather generally when inorganic materials are appropriately deposited onto softened (or subsequently softened) organic polymer substrates; partially embedded structures are generally formed by organic particulate materials, although these can also be embedded by exposure to a solvent vapour. For both rigid preformed particles spread onto the polymer surface, and for flexible growing clusters (as occur in vacuum deposition), the tendency for complete immersion is thermodynamically determined by the same simple inequality among the surface and interfacial tensions. Modelling of the polymer molecule configurations in the vicinity of subsurface particles predicts a novel entropic force of sufficient magnitude to explain why the particles form a monolayer a few tens of nm below the surface, rather than dispersing throughout the polymer, and why this structure is remarkably stable on extended heating. With the convenient fabrication technique of vacuum deposition, subsurface formation is further limited kinetically, by growth mode and sinking rate considerations, to generally low melting point inorganics and to certain ranges of deposition conditions; once subsurface particles are formed, their subsequent growth during the deposition process generally occurs at constant (nearly close-packed) surface coverage by a combination of material-capture and coalescence. After these nearly monodisperse particles grow beyond ~0.4 μm, they begin to bridge into a continuous subsurface structure. These vacuum-deposition phenomena are quantitatively explained by kinetic models of the formation and growth mechanisms.

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