Surfaces binary polymer blends

The wall-PRISM theory has also been implemented for binary polymer blends. For blends of stiff and flexible chains the theory predicts that the stiffer chains are found preferentially in the immediate vicinity of the surface [60]. This prediction is in agreement with computer simulations for the same system [59,60]. For blends of linear and star polymers [101] the theory predicts that the linear polymers are in excess in the immediate vicinity of the surface, but the star polymers are in excess at other distances. Therefore, if one looks at the integral of the difference between the density profiles of the two components, the star polymers segregate to the surface in an integrated sense, from purely entropic effects. 

SCFT today is one of the most commonly used tools in polymer science. SCFT is based on de Gennes-Edwards description of a polymer molecule as a flexible Gaussian chain combined with the Flory-Huggins "local" treatment of intermolecular interactions. Applications of SCFT include thermodynamics of block copolymers (Bates and Fredrickson, 1999 Matsen and Bates, 1996), adsorption of polymer chains on solid surfaces (Scheutjens and Fleer, 1979,1980), and calculation of interfacial tension in binary polymer blends compatibilized by block copolymers (Lyatskaya et al., 1996), among others. 

Hariharan, A., Kumar, S.K., Russell, T.P. Reversal of the isotopic effect in the surface behavior of binary polymer blends. J. Chem. Phys. 98, 41634173 (1993)... 

Genzer, J., Faldi, A., Composto, R.J. Self-consistent mean-field calculation of surface segregation in a binary polymer blend. Phys. Rev. E Stat. Phys. Plasmas Fluids 50, 2373-2376(1994)... 

Bitinis et developed for the first time a novel and industrially scalable PLA-NR blend prepared by melt mixing blends at 5,10 and 20 wt% of natural rubber to analyze the effect of the NR concentration on the blend morphology. Figure 7.5 shows SEM micrographs of the blends fracture surfaces where it is observed that the size of the rubber particles is similar for 5 and 10 wt% but increases for the blend at 20 wt% from 1.15 to 2.00 pm. In general, in an immiscible binary polymer blend, the size of the dispersed phase increases as a function of the concentration of the minor phase in the blend, due to coalescence phenomena. ... 

Figure 15 (a) Phase diagram of a binary polymer blend N= 32) as obtained from Monte Carlo simulations of the bond fluctuation model. The upper curve shows the binodais in the infinite system the middle one corresponds to a thin film of thickness D=2.8/ e and symmetric boundary fields [wall = 0.16, both of which prefer species A (capillary condensation). The lower curve corresponds to a thin film with antisymmetric surfaces (interface localization/delocalization). The arrow marks the location of the wetting transition. Full circles mark critical points open circles/dashed line denotes the triple point, (b) Coexistence curves in the (T, A/y)-plane. Circles mark critical points, and the diamond indicates the location of the wetting transition temperature. It is indistinguishable from the temperature of the triple point. Adapted from Muller, M. Binder, K. Phys. Rev. 2001, 63, 021602. ... 

Figure 16 Composition profiles of the interface between two laterally coexisting phases in a thin film with symmetric surface interactions as obtained from Monte Carlo simulations of a binary polymer blend. A-rich regions are shaded light B-rich regions are shaded dark, (a) Corresponds to a temperature above the wetting transition temperature T S.STwet-There are A-enrichment layers in the B-rich region, and the AB interface does not approach the wall. The thickness, h, of the A-rich surface enrichment layers in the B-rich phase is indicated by an arrow.

Figure 18 (a) Binodals of a symmetric, binary polymer blend confined into a film of thickness D= 2.6/ e as obtained by self-consistent field calculations. The strength of preference at one surface is kept constant. The surface interactions at the opposite surface vary, and the ratio of the surface interactions is indicated in the key. +1.0 corresponds to a strictly symmetric film, and -1.0 marks the interface localization-delocalization transition that occurs in an antisymmetric film. The dashed curve shows the location of the critical points. Filled circles mark critical points and open circles/dashed horizontal lines denote the three-phase coexistence (triple point) for - 0.735 and -1.0. The inset presents part of the phase boundary for antisymmetric boundaries, (b) Schematic temperature dependence for antisymmetric boundaries. The three profiles correspond to the situations (u), (m), and (I) in the inset of (a), (c) Coexistence curves in the// /-A/y plane. The ratio of surface interactions varies according to the key. The analogs of the prewetting lines for A//pw< 0 and ratios of the surface interactions, -0.735 and -1.0, are indistinguishable, because they are associated with the prewetting behavior of the surface with interaction, which attracts the A-component. Reproduced from Muller, M. Binder, K. Albano, E. V. Europhys. Lett. 2000, 50, 724-730, with authorization of http //epljournal.edpsciences.org/... 

Surface-induced phase separation of binary polymer blends on the chemically patterned substrate. Poiym. Bull., 55, 131-140. 

In a large part of what we have discussed above, we considered binary polymer mixtures. However, the situation is somewhat different, if instead of polymer blends, thin films of block copolymers are investigated. Due to the molecular connectivity of the different blocks, the inherent length scale is now determined by the size of the molecules. Early experiments focussed on the thin film morphology in symmetric diblock copolymers, where surface interactions tend to orient the block copolymer lamellae parallel to the boundary surfaces. In contrast to most bulk specimens, the planar interfaces lead to the formation... 

A crucial aspect on polymer blends containing block copolymers concerns the concentration of block copolymer both in bulk and at the surface. The former can be controlled in the design of the initial blend and the latter depends not only on the amount initially introduced in the blend but also on the eventual surface segregation. In Fig. 5.18 is schematically illustrated the block copolymer arrangement of binary blends with variable amount of block copolymer. At low concentrations (a, b) the block copolymer can reside either in the bulk or at the interface and the amount of block copolymer segregated at the interface is directly related to the... 

Scheffold, F., Budkowski, A., Steiner, U., Eiser, E., Klein, J., Fetters, L.J. Surface phase behavior in binary polymer mixtines. II. Surface emichment Irom polyolefin blends. J. Chem. Phys. 104, 8795-8806 (1996)... 

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