Fluctuation phenomena in structurally symmetric polymer blends

Journal Article · Wed Feb 01 00:00:00 EST 1995 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.468741· OSTI ID:6654562

Singh, C; Schweizer, K S ^[1]; Yethiraj, A ^[2]

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1. Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)
2. Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706 (United States)

Polymer reference interaction site model theory with the new molecular closures is used to study structurally and interaction potential symmetric binary blends. Both compressibility and free energy routes to thermodynamics are studied and thermodynamic consistency is addressed. Various non-Flory-Huggins effects, or fluctuation phenomena,'' are found: nonuniversal renormalization of critical temperature and effective chi-parameter from mean field values, composition-dependent chi-parameters, and nonlinear dependence of inverse osmotic compressibility on inverse temperature. These fluctuation effects depend on degree of polymerization, [ital N], chain length asymmetry, polymer density, range and precise form of attractive tail potentials, chain stiffness, and proximity to phase boundary. Some fluctuation effects are intrinsic, i.e., survive in the long chain [ital N][r arrow][infinity] limit, while others are finite size effects which arise from chain-connectivity-induced coupled local density and long wavelength concentration fluctuations. Due to multiple sources of fluctuation effects, even asymptotic finite size effects can appear intrinsic'' over extended ranges of [ital N]. Comparison with lattice Monte Carlo simulations of Deutsch and Binder shows good agreement with theory. All fluctuation effects can be understood in simple terms by examining enthalpy of mixing and local interchain correlations. Key physical process is thermally driven local interchain rearrangements corresponding to formation of diffuse interfaces and clusters or droplets. Analytic results are derived using the Gaussian thread model, which provides a simple physical understanding of the origin of numerically determined fluctuation effects. In the long chain limit predictions for the thread blend are shown to be exactly thermodynamically consistent, a unique circumstance for liquid state theories.

• DOE Contract Number: FG02-91ER45439
• OSTI ID: 6654562
• Journal Information: Journal of Chemical Physics; (United States), Vol. 102:5; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BINARY MIXTURES
FLUCTUATIONS
POLYMERS
ANALYTICAL SOLUTION
ASYMMETRY
CHAINS
CHEMICAL COMPOSITION
COMPRESSIBILITY
CORRELATIONS
CRITICAL TEMPERATURE
FREE ENERGY
GAUSS FUNCTION
LENGTH
MEAN-FIELD THEORY
NONLINEAR PROBLEMS
NUMERICAL SOLUTION
OSMOSIS
POLYMERIZATION
RENORMALIZATION
THERMODYNAMICS
CHEMICAL REACTIONS
DIFFUSION
DIMENSIONS
DISPERSIONS
ENERGY
FUNCTIONS
MECHANICAL PROPERTIES
MIXTURES
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
VARIATIONS
360602* - Other Materials- Structure & Phase Studies