Entropic Contributions to Bare Surface Free Energy fs

Entropic Contributions to Bare Surface Free Energy fs 

The Cahn analyses already performed for early surface enrichment observations [167,170] have shown that the yielded relation of the surface energy derivative (—dfs/dc]))s vs (] , cannot be described by the linear form suggested by simple arguments presented above. While it can be argued that the more sophisticated enthalpy-based models (e.g., [185]) might eventually account for these discrepancies, the relation (—dfs/dc]))s has been interpreted with the Cohen and Muthuku-mar model [183] instead. This model considers entropic effects due to the restriction of the configuration of polymers in the vicinity of an external interface (surface) and finds the additional entropic contribution to the bare surface free energy fss to be equal to 

The surface segregation from the mixture of chemically identical polymers with chain length disparity is predicted by another model [198-200]. It represents the spatial conformation of a polymer coil as a random walk reflected by an external interface. The associated loss in system configurations is minimized when shorter chains are adsorbed at the surface. Preferential surface seg- 

The divergent predictions of theories on entropic surface segregation advocating the surface enrichment in more flexible [184, 186, 205, 206], more stiff [200,204,207,209,214], or both types of molecules [183,208] may be compared with experimental results obtained for blends composed of the statistical olefines E EEx. The more branched (i.e., more flexible) component was found preferred at the free surface (with an exception of enrichment-depletion duality described in Sect. 3.1.2.4) but no segregation was observed at silicon or gold interfaces. This leads to the conclusion [120] that the entropic driving force alone cannot be in charge of the enrichment because in such a case the enrichment 

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Entropic Contributions to "Bare"Surface Free Energy fs... 

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