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Film formation of crystallizable polymers on microheterogeneous surfaces

Dewetting and crystallization of thin polyethyleneoxide (PEO) films obtained by dip-coating on microheterogeneous surfaces are investigated. Formation of thin polymer films and crystallization are characterized as sequential processes. Film topography and morphology are influenced by surface pattern geometry and polymer solution properties. Under appropriate experimental conditions in which heterogeneous nucleation is avoided, ultrathin non-crystalline PEO films can be prepared which are stable with respect to crystallization over a long time. The experimental procedure established generates films by dewetting on microheterogenous surfaces in which isolated amorphous micrometre-sized areas surrounded from non-wetting barriers are formed. Within these amorphous PEO areas, crystallization can be initiated on request with respect to starting time and location. The crystallization in ultrathin PEO films results in highly branched lamella morphology arising from a diffusion limited aggregation processes (DLA). As time and location for onset of diffusion limited crystallization can be chosen, the morphological features characteristic for DLA growth processes such as correlation width and growth direction of branches can be tuned. In addition, influences of limited material reservoirs in confined areas on film morphology are discussed.