Is Compressibility Important in the Thermodynamics of Polymer Mixtures?

Kumar, Sanat K.; Veytsman, Boris; Maranas, Janna K.; Crist, Buckley

doi:10.1103/physrevlett.79.2265

Cited by 17 publications

(23 citation statements)

References 15 publications

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“…In previous work we showed that a SANS measurement, when properly corrected for density fluctuations and for the dissimilar volumes of the two components, yields estimates of the osmotic susceptibility [∂ 2 ∆g/∂φ 2 ] T,P -1 . 16,17 Here we briefly discuss these previous findings, and also connect them to the standard random phase approximation (RPA) expression, which is traditionally used to analyze SANS data from polymer blends. Note that we consider experimentally relevant isothermal-isobaric conditions, and hence x, the mole fraction of monomers of species 1, and ∆g, the Gibbs free energy of mixing per mole of monomers, are the natural variables.…”

Section: Pressure Dependence Of Scattering Intensitymentioning

confidence: 89%

Pressure Effects on the Thermodynamics of Polymer Blends

Kumar

2000

Macromolecules

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Simple thermodynamic arguments are evoked to show that the pressure dependence of the Flory interaction parameter of miscible polymer blends, as derived from small-angle neutron scattering experiments, is directly related to the volume changes on mixing for these systems. This approach is validated by comparison to available experimental data. We make contact with existing theoretical approaches and show that it is thermodynamically inconsistent to model a blend with nonzero as having no volume change on mixing. Since the entropic contributions that arise from these volume changes on mixing account for more than 50% of the pressure dependence of , the use of regular solution theory, where the pressure dependence is purely enthalpic in origin, gives an imperfect understanding of these situations. We finally show that, since the volume change on mixing is directly proportional to the parameter under ambient pressures, the critical temperature for any polymer blend will vary in an apparently "universal" fashion on pressurization. This conclusion is in agreement with experimental data for a large number of polymer blends. IntroductionThe role of pressure on the thermodynamics of polymer mixtures has been intensely studied in the past few years since it has direct applications to processing and to novel synthesis schemes involving environmentally benign supercritical fluids. Pressure effects are also of interest from a fundamental standpoint since the thermodynamics of typical polymer blends are understood in the framework of the incompressible random phase approximation. 1-6 A rigorously incompressible system should be unaffected by pressure. However, since experimental results show that the critical temperature for polymer-polymer demixing, T c , is strongly affected by pressure, typically dT c /dP ≈ 25-50 K/kbar, it is clear that polymer blends show significant departures from this ideal limit. 5,7 Most successful approaches in this area incorporate free volume effects, either into the free energy of the system or into an equation of state. The pressure dependence of T c and , the Flory-Huggins interaction parameter, is then numerically derived. 7-14 While these methods have been quite successful at explaining the measured dT c /dP, they provide little physical insight into the effect of pressure.A line of thinking that helps build a picture at the molecular level for the effect of pressure on polymer blend thermodynamics is presented by Rabeony et al. 6 Here it is postulated that the central quantity is the interaction energy density, X ≡ ( /v 0 )RT. is the Flory interaction parameter, 15 v 0 is an arbitrary reference volume, R is the gas constant, and T is the temperature. The X values obtained from some of the blends considered appear to be unique functions of system density, and data from several pressures and temperatures for each of these systems can be collapsed onto a master curve. Since this approach explicitly assumes that volume changes on mixing are negligible, it suggests that the only role of pressu...

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Section: Pressure Dependence Of Scattering Intensitymentioning

confidence: 89%

Pressure Effects on the Thermodynamics of Polymer Blends

Kumar

2000

Macromolecules

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“…However, the magnitude of experimentally observed parabolic contributions cannot be explained by Eqn. (4) alone [43].…”

Section: Polymer Incompatibility and Flory Huggins Parametermentioning

confidence: 99%

“…(2),inter ij (r)/̺ i is independent of i, one still expects local composition fluctuations. Such "nonrandom-mixing" also affects the demixing behaviour [43], especially very close to the critical point [48]. According to the Ginzburg criterion [18], however, the random-mixing approximation becomes better upon increasing the chain length [49].…”

Section: Polymer Incompatibility and Flory Huggins Parametermentioning

confidence: 99%

Monte Carlo Simulations of Interfaces in Polymer Blends

Mueller

Schmid

1999

Annual Reviews of Computational Physics VI

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We review recent simulation studies of interfaces between immiscible homopolymer phases. Special emphasis is given to the presentation of efficient simulation techniques and powerful methods of data analysis, such as the analysis of capillary wave spectra. Possible reasons for polymer incompatibility and ways to relate model dependent interaction parameters to an effective Flory Huggins parameter χ are discussed. Various interfaces are then considered and characterised with respect to their microscopic structure and thermodynamic properties. In particular, interfaces between homopolymers of equal or disparate stiffness are studied, interfaces containing diblock copolymers, and interfaces confined in thin films. The results are related to the phase behaviour of ternary homopolymer/copolymer systems, and to wetting transitions in thin films.

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“…The phase behavior of multi‐component polymeric materials has been of great interest and has been studied both experimentally and theoretically, since phase behavior is key to the compatibility in most applications involving polymer blends and block copolymers 1–23. Two characteristic features of phase transitions can be described by the temperature dependence of the Flory interaction parameter ( χ ) such as the upper critical solution transition (UCST) and the lower critical solution transition (LCST).…”

Section: Introductionmentioning

confidence: 99%

“…Two characteristic features of phase transitions can be described by the temperature dependence of the Flory interaction parameter ( χ ) such as the upper critical solution transition (UCST) and the lower critical solution transition (LCST). Upon cooling in the weakly interacting binary blends, UCST‐type polymer blends generally undergo a transition from the homogeneous to phase‐separated state by non‐favorable segmental interactions, while LCST‐type blends show an opposite tendency as a consequence of the thermal compressibility (or thermal expansion) difference between two components 8–19…”

Section: Introductionmentioning

confidence: 99%

Phase Behavior of a Weakly Interacting Polystyrene and Poly(n‐hexyl methacrylate) System: Evidence for the Coexistence of UCST and LCST

Ahn

Naidu

Ryu

et al. 2009

Macromol. Rapid Commun.

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The phase behavior of a weakly interacting binary system composed of deuterated polystyrene (dPS) and poly(n-hexyl methacrylate) (PnHMA) was investigated by the turbidity measurement for the binary blend, and by small angle X-ray scattering (SAXS) and depolarized light scattering for the block copolymers. For the binary dPS/PnHMA blend, a new phase diagram involving both the upper critical solution transition (UCST) and lower critical solution transition (LCST) was observed by the delicate control of molecular weights between dPS and PnHMA. Whereas for the block copolymers such as dPS-block-PnHMA and PS-block-PnHMA, an order-to-disorder transition (ODT) on heating was observed within the experimental temperature range depending on the molecular weight. This coexistence of both a UCST and LCST in the dPS/PnHMA blend consequently represents the experimental evidence that the corresponding (d)PS-b-PnHMAs possess not only ODT, but also lower disorder-to-order transition (LDOT) character driven by a compressibility difference, although the latter is hindered by thermal degradation.

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Is Compressibility Important in the Thermodynamics of Polymer Mixtures?

Cited by 17 publications

References 15 publications

Pressure Effects on the Thermodynamics of Polymer Blends

Pressure Effects on the Thermodynamics of Polymer Blends

Monte Carlo Simulations of Interfaces in Polymer Blends

Phase Behavior of a Weakly Interacting Polystyrene and Poly(n‐hexyl methacrylate) System: Evidence for the Coexistence of UCST and LCST

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