Liquid–liquid equilibria of binary polymer solutions with specific interactions

Chang, Bong Ho; Bae, Young Chan

doi:10.1016/s0032-3861(97)10386-x

Cited by 20 publications

(16 citation statements)

References 30 publications

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“…An important alternative mechanism for the occurance of lower critical solution points or close loop phase behavior are specific interactions (e. g., hydrogen bonds) between monomers. The effects of hydrogen bonds on the phase behavior have attracted longstanding interest [15][16][17][18] . This mean field picture has been investigated via Monte Carlo simulations 35) in the bond fluctuation model with the indented monomers sketched in Fig.…”

Section: Symmetric Blendsmentioning

confidence: 99%

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Miscibility behavior and single chain properties in polymer blends: a bond fluctuation model study

Müller¹

1999

Macromol. Theory Simul.

106

113

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SUMMARY: Computer simulation studies on the miscibility behavior and single chain properties in binary polymer blends are reviewed. We consider blends of various architectures in order to identify important architectural parameters on a coarse grained level and study their qualitative consequences for the miscibility behavior. The phase diagram, the relation between the exchange chemical potential and the composition, and the intermolecular pair correlation functions for symmetric blends of linear chains, blends of cyclic polymers, blends with an asymmetry in cohesive energies, blends with different chain lengths, blends with distinct monomer shapes, and blends with a stiffness disparity between the components are discussed. For strictly symmetric blends the Flory-Huggins theory becomes quantitatively correct in the long chain length limit, when the v parameter is identified via the intermolecular pair correlation function. For small chain lengths composition fluctuations are important. They manifest themselves in 3D Ising behavior at the critical point and an upward parabolic curvature of the v parameter from small-angle neutron scattering close to the critical point. The ratio between the mean field estimate and the true critical temperature decreases like v p aqb 3 for long chain lengths. The chain conformations in the minority phase of a symmetric blend shrink as to reduce the number of energeticaly unfavorable interactions. Scaling arguments, detailed self-consistent field calculations and Monte Carlo simulations of chains with up to 512 effective segments agree that the conformational changes decrease around the critical point like 1a N p . Other mechanisms for a composition dependence of the single chain conformations in asymmetric blends are discussed. If the constituents of the blends have non-additive monomer shapes, one has a large positive chain-length-independent entropic contribution to the v parameter. In this case the blend phase separates upon heating at a lower critical solution temperature. Upon increasing the chain length the critical temperature approaches a finite value from above. For blends with a stiffness disparity an entropic contribution of the v parameter of the order 10 -3 is measured with high accuracy. Also the enthalpic contribution increases, because a back folding of the stiffer component is suppressed and the stiffer chains possess more intermolecular contacts. Two aspects of the single chain dynamics in blends are discussed: (a) The dynamics of short non-entangled chains in a binary blend are studied via dynamic Monte Carlo simulations. There is hardly any coupling between the chain dynamics and the thermodynamic state of the mixture. Above the critical temperatures both the translational diffusion and the relaxation of the chain conformations are independent of the temperature. (b) Irreversible reactions of a small fraction of reactive polymers at a strongly segregated interface in a symmetric binary polymer blend are investigated. End-functionalized homopolymers of different...

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Section: Symmetric Blendsmentioning

confidence: 99%

“…Such behavior is observed in binary polymer solutions and blends 14) . Specific interactions (e. g., hydrogen bonds [15][16][17][18] ) might also give rise to a phase separation upon heating. Moreover, the v parameter often depends on composition and chain length as well.…”

Section: Introductionmentioning

confidence: 99%

Miscibility behavior and single chain properties in polymer blends: a bond fluctuation model study

Müller¹

1999

Macromol. Theory Simul.

106

113

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“…FloryHuggins theory [3,4] is the most widely used and wellknown lattice model, which in a simple way illustrates the competition between the entropy of mixing and the attractive forces among the molecules in polymer solutions. However, the Flory-Huggins [3,4] model cannot predict the lower critical solution temperature (LCST) for the polymer solutions [5][6][7]. The appearance of the LCST is attributed to the existence of the free-volume differences between the polymer and solvent molecules.…”

Section: Introductionmentioning

confidence: 99%

A free-volume modification of GEM-QC to correlate VLE and LLE in polymer solutions

Radfarnia

Taghikhani

Ghotbi

et al. 2004

The Journal of Chemical Thermodynamics

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“…The second term in equation (1), ln c resid i , is the residual part of the UNIQUAC-NRF model and takes the same form as that in the UNIQUAC-NRF model [14]. In equation (1), the combinatorial part can be expressed according to the following equation:…”

Section: Theorymentioning

confidence: 99%

“…In generally, the LCST in a polymer solution occurs when an unfavorable entropy effect, negative entropy of mixing, overcomes the negative enthalpies of mixing. The LCST is associated with large differences in thermal expansion of solvent and solute or difference in free-volume percentage between polymer and solvent [1][2][3]. On the other hand, the appearance of the LCST is attributed to the existence of the free volume differences between polymer and solvent molecules.…”

Section: Introductionmentioning

confidence: 99%

(Liquid+liquid) equilibria of binary polymer solutions using a free-volume UNIQUAC-NRF model

Radfarnia

Ghotbi

Taghikhani

et al. 2006

The Journal of Chemical Thermodynamics

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Liquid–liquid equilibria of binary polymer solutions with specific interactions

Cited by 20 publications

References 30 publications

Miscibility behavior and single chain properties in polymer blends: a bond fluctuation model study

Miscibility behavior and single chain properties in polymer blends: a bond fluctuation model study

A free-volume modification of GEM-QC to correlate VLE and LLE in polymer solutions

(Liquid+liquid) equilibria of binary polymer solutions using a free-volume UNIQUAC-NRF model

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