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We examined the effect of the addition of homopolymers tetramethylbisphenol A polycarbonate, TMPC, and poly(norbornene−methyl-d 3-carboxylate), NBMC, on the interlamellar spacing and the phase stability of symmetric poly(styrene-b-methyl methacrylate) diblock copolymer thin films on silicon substrates. The films were of thickness h, L < h < 5L, where L is the interlamellar spacing of the microphase separated PS-b-PMMA diblock copolymer. The homopolymers considered had degrees of polymerization, N TMPC and N NBMC, comparable to one-half of the degree of polymerization of the diblock. In the TMPC/diblock blend, for low TMPC homopolymer concentrations, φTMPC < 0.2, the homopolymer chains were localized in the middle of the PS micro-ordered domains, and the interlamellar spacing increased as L/(1 − φTMPC). For φTMPC > 0.2 the morphology of the diblock copolymer changed to accommodate higher volume fractions of TMPC. This behavior is contrasted with earlier observations in the PS-b-PMMA/PS homopolymer system where this diblock accommodated considerably higher PS homopolymer volume fractions while maintaining a lamellar phase. In the NBMC/diblock system the interlamellar spacing increased as L/(1 − φNBMC) for homopolymer concentrations up to φNBMC ≈ 0.05. For φNBMC > 0.05, the NBMC formed a pure layer on the substrate, with the diblock maintaining its microphase separated structure on this layer. These results are discussed in light of mean field theory and in terms of the effect of the interfacial constraints on the phase behavior.

Articles you may be interested inOn the comparisons between dissipative particle dynamics simulations and self-consistent field calculations of diblock copolymer microphase separation Effects of interaction range and compressibility on the microphase separation of diblock copolymers: Mean-field analysis Polymer reference interaction site model ͑PRISM͒ based density functional ͑DF͒ theory is used to evaluate the structure and thermodynamics of structurally symmetric, freely jointed, diblock chains with 0.50 volume fraction. These results are compared to the results of self-consistent-field ͑SCF͒ theory. Agreement between the predictions of the SCF and DF theories is found for the lamella spacing well above the order-disorder transition ͑ODT͒ and for the qualitative behavior of the interfacial thickness as a function of both chain length and Flory-Huggins parameter. Disagreement is found for the magnitude of the interfacial thickness where DF theory indicates that the thickness is 1.7Ϯ0.2 times larger than that predicted by SCF theory. It appears that behavior on the monomer length scale is sensitive to system specific details which are neglected by SCF theory.

Polyatomic density functional theory is applied to a binary polymer blend. The polymer reference interaction site model (PRISM) liquid state theory provides the homogeneous state correlation functions necessary for the application of density functional theory. An effective chi parameter can be recognized from the density functional expression; however, the phase separation criteria does not depend solely upon the chi parameter, rather it depends upon various combinations of the species‐dependent direct correlation functions of the blend. The Flory‐Huggins chi parameter along with the associated phase diagram is obtained when the monomer volumes of the blend species are equal and for a range of monomer‐monomer attractive interactions. Calculations are performed both with and without the assumption of incompressibility. The density functional theory along with the PRISM determined “input” predict that an isotopic polymer blend shows an upper critical solution temperature (UCST) phenomena. © 1995 John Wiley & Sons, Inc.