Surface effects on polymer blends and block copolymer melts: Theoretical concepts of surface enrichment, surface induced phase separation and ordering

Abstract

Surfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface-induced transitions (formation of wetting layers, surface-directed spinodal decomposition, surface-induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory-Huggins-de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentioned briefly.concentration (e), there is a coexistence curve separating the one-phase region (above) from the two-phase region (below) in the bulk.This two-phase region ends at Teb in a bulk critical point (without loss of generality we assume an upper critical solution temperature (UCST) here).The difference dQ= &,& -&,& is the "order parameter"of the transition describing phase separation in the two coexisting phases (&izd,,, &J. The wetting transition is a singularity of the surface excess free energy associated with the wall and occurs at T, for a path along the coexistence curve. The corresponding order parameter profile may change from a nonwet state of the surface (surface excess order parameter e,, the integral of the shaded region, being finite) to a wet state in either a continuous fashion ("critical wetting") or via a discontinuous jump at T, ("first-order wetting"). The schematic "adsorption isotherms" in the lower part of the figure show the behavior as a function of a control parameterp approaching the coexistence curve from the one-phase region atp,,,, @=pressure for the fluid, orp=chemical potential difference d p for a mixture, etc.). When e,-one then has"comp1ete wetting"whi1e Q~@~~~~) <-(for T< T,) means "incomplete wetting". For T, < T < Cre a further discontinuity occurs at the "prewetting transition".Fax: +49-6 13 1-3 9-5 44 1

Effect of deuterium substitution on the surface interactions in binary polymer mixtures

“…The bulk and surface thermodynamical properties of polymer mixtures have been a topic of considerable interest from a fundamental 1 as well as from an applications 2 point of view. Over the last decade much experimental and theoretical work has focused on model systems of polymer mixtures formed by molecules with different isotopic or/and microstructural composition.…”

Surface segregation of conformationally asymmetric polymer blends

“…However, in contrast to the effective surface Hamiltonian used in many studies [1] the corresponding terms are not localized at the surface only [28]. The integration over the field Φ(r) can be performed in the same way as for bulk.…”

“…[1]. The structure and properties of the blends and other polymeric materials within a few nanometers at a surface can differ significantly from corresponding properties in the bulk.…”

Elasticity Dominated Surface Segregation of Small Molecules in Polymer Mixtures

“…Several industrial formulations, e.g., chocolate [4], food packaging [5], etc., suffer from this ubiquitous problem. While many experimental [1,2,6] and theoretical studies [7] of this phenomenon exist, a good quantitative agreement between theoretical predictions and experiments is still lacking [1]. Further, experimental strategies to control the amount of material migrating to the surface is in a nascent stage of development.…”