Nonrandom mixing in polymer blends: Implications for phase behavior

Foreman, K. W.; Freed, Karl F.; Ngola, Isaac M.

doi:10.1063/1.474830

Cited by 18 publications

(14 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast, for a carefully selected system with chemically similar monomers, where x is positive but small, there exists a possibility for DV mix , 0. These predictions are consistent with the recent work of Foreman and Freed [7] using the lattice cluster model. Such situations, which would result in a previously unobserved pressure induced compatibilization, are the focus of this paper.…”

supporting

confidence: 92%

“…A similar increase of x s with P (,800 bars) was the origin of the decrease of the order-disorder phase transition in a diblock copolymer [16]. It is important to stress, as noted by Dudowicz and Freed [7], that a critical factor governing the thermodynamics of block copolymers is the junction point between the two blocks. Since a block copolymer is therefore a truly single component system, it is hard to relate its behavior to that of a blend, which is a physical mixture.…”

mentioning

confidence: 94%

See 1 more Smart Citation

Pressure-Induced Compatibility in a Model Polymer Blend

et al. 1998

View full text Add to dashboard Cite

Photon correlation spectroscopy measurements on mixtures of chemically similar polymers close to their phase boundary show that pressure enhances their miscibility. This unexpected result, which is shown to be caused by negative excess volume changes on mixing for this partially miscible blend, stresses that pressure can play a complex role in determining the miscibility and hence the processing of polymeric mixtures. [S0031-9007 (98)06644-7] PACS numbers: 61.41. + e, 64.60.Ht, 64.75. + g The phase separation of polymer blends is primarily driven by the reduced entropy of mixing as compared to small molecule analogs [1]. This basic fact is captured by incompressible Flory-Huggins (FH) theory [2], which predicts that the free energy of mixing per lattice site, DG mix , isN A and N B are the degrees of polymerization for the two polymers, and f is the volume fraction of species A [1]. x~͑2´1 2 2´1 1 2´2 2 ͒ is the interaction parameter which has a purely enthalpic origin in the theory, and´i j is the energy of interaction between a nearest neighbor i-j pair. In contrast to these ideas experimental work has established that additional factors, not incorporated in FH theory, can play an important role. x has therefore been assumed to be of the general form,x ϵ x h ͞T 2 x s , where x h ͞T and x s are usually interpreted as the enthalpic and entropic contribution, respectively [3,4]. An important factor determining blend behavior is their finite compressibility, an issue which is important, for example, when blend phase behavior is studied as a function of pressure [5]. Note that the FH theory, being incompressible, would suggest that pressure is an irrelevant variable. Relative standard thermodynamics [6] shows that the pressure dependence of the critical temperature is ͑≠T c ͞≠P͒ f TDV mix ͞DH mix . Since DH mix , the enthalpy change on mixing, is positive at the critical point, the sign of this derivative is controlled by DV mix , the volume change on mixing. In all polymer blends investigated to date ͑≠T c ͞≠P͒ f . 0 implying that DV mix . 0. A simple equation of state, such as the lattice fluid model (which extends FH theory through the addition of free volume [3]), shows that to leading order DV mix f͑1 2 f͒ ͕4x 2 ͓͑´1 1 2´2 2 ͒͞RT͔ 2 ͖. For many common blends, such as those studied in past work, the x parameter is large, and therefore the lattice model predicts DV mix . 0. In contrast, for a carefully selected system with chemically similar monomers, where x is positive but small, there exists a possibility for DV mix , 0. These predictions are consistent with the recent work of Foreman and Freed [7] using the lattice cluster model. Such situations, which would result in a previously unobserved pressure induced compatibilization, are the focus of this paper. We conducted free space Monte Carlo simulations on mixtures of chains, where both components are of length N 25. These simulations build on our past work [8] where we considered that the monomers on the different chains interacted through standard Lennard-Jo...

show abstract

supporting

confidence: 92%

mentioning

confidence: 94%

Pressure-Induced Compatibility in a Model Polymer Blend

et al. 1998

View full text Add to dashboard Cite

show abstract

“…The technical details and the diagrammatic representation of F blend for both fully flexible and semiflexible chain blends are described in a series of papers. 14,[19][20][21] A similar expression for the free energy of a melt follows directly from Eq. ͑8͒ by setting 1 ϭ and 2 ϭ0.…”

Section: Free Energy Of Binary Polymer Blendsmentioning

confidence: 99%

“…13 The lattice cluster theory also describes the influence of chain semiflexibility on the properties of polymer blends. 14 The variation of blend thermodynamic properties and miscibility with chain semiflexibility is explained in the LCT by using a few rather simple effective geometrical parameters that depend on the monomer molecular structures and on the energy differences between trans and gauche conformations. The present comparisons of LCT calculations with SANS data demonstrate that the inclusion of chain semiflexibilty into the LCT significantly improves the ability of the theory to describe the temperature, pressure, and microstructure dependence of the SANS effective FH parameter.…”

Section: Introductionmentioning

confidence: 99%

Small-angle neutron scattering studies of polybutadiene/polystyrene blends as a function of pressure and microstructure: Comparison of experiment and theory

Frielinghaus

Schwahn

Dudowicz

et al. 2001

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

Small-angle neutron scattering ͑SANS͒ experiments have been performed for three polybutadiene/ polystyrene ͑dPB/PS͒ blends of differing dPB microstructure as a function of pressure and temperature. The experimental effective SANS interaction parameters are analyzed using the mean-field lattice cluster theory ͑LCT͒. In order to provide a meaningful comparison with the LCT, contributions from the non-mean-field long-range composition fluctuations are removed from the experimental data by use of a crossover function that describes the transition between near-critical and mean-field behaviors for the extrapolated zero-angle scattering. The theory provides a good description of the overall pressure dependence of the effective interaction parameter and its small dependence on the percentage of 1,2 addition units in the dPB chains.

show abstract

“…In this formulation, the χ parameter is a convenient measure of the excess Gibbs free energy. The combined effects in χ include contributions possibly from enthalpic interactions, equation‐of‐state effects such as volume changes upon mixing, conformational entropy effects such as local packing, and noncombinatorial entropic terms 16, 28. As a result, although the χ parameter provides a standardized, conveniently comparable measure of blend interactions, it needs to be considered in terms of the relative importance of the various effects that are implicit in the definition.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic interactions in blends of poly(4‐tert‐butyl styrene) and polyisoprene by small‐angle neutron scattering

Yurekli

Krishnamoorti

2004

J Polym Sci B Polym Phys

View full text Add to dashboard Cite

The thermodynamic interactions between poly(4-tert-butyl styrene) [P(4tBS)] and 1,4-polyisoprene (PI; both hydrogenous) were obtained as functions of the temperature, PI molecular weight, and blend composition through the examination of miscible ternary blends of these two components with a common miscible labeled polymer [90% 1,2-deuterated polybutadiene (dPBD)] with small-angle neutron scattering. The thermodynamic interaction parameters between P(4tBS) and dPBD and between P(4tBS) and PI increased with increasing temperature and were consistent with lower critical solution temperature behavior. Although the binary blends of P(4tBS) and dPBD exhibited phase separation at elevated temperatures, the thermodynamic interaction parameters between P(4tBS) and PI remained large and negative and independent of the PI molecular weight. Finally, the thermodynamic interactions for PI and P(4tBS) depended strongly on the ratio of PI to P(4tBS) and were also sensitive to the amount of dPBD present in the ternary blend.

show abstract

Nonrandom mixing in polymer blends: Implications for phase behavior

Cited by 18 publications

References 29 publications

Pressure-Induced Compatibility in a Model Polymer Blend

Pressure-Induced Compatibility in a Model Polymer Blend

Small-angle neutron scattering studies of polybutadiene/polystyrene blends as a function of pressure and microstructure: Comparison of experiment and theory

Thermodynamic interactions in blends of poly(4‐tert‐butyl styrene) and polyisoprene by small‐angle neutron scattering

Contact Info

Product

Resources

About