On the vapor-liquid equilibrium of attractive chain fluids with variable degree of molecular flexibility

Westen, Thijs van; Vlugt, Thijs J. H.; Groß, Joachim

doi:10.1063/1.4922264

Cited by 6 publications

(10 citation statements)

References 87 publications

(134 reference statements)

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“…For details on the equations for calculating the different contributions, the reader is referred to the work of van Westen et al [71]. Details on the development of the different contributions to the equation of state can be found elsewhere [81,[102][103][104][105].…”

Section: Resultsmentioning

confidence: 99%

“…Another theoretical assumption that could explain the observed deviations is the use of a fixed temperature-independent aspect ratio of the molecules. This assumption is typically needed in a perturbed-chain approach [105]; however, it reduces the driving force for the isotropic to nematic phase transition as the aspect ratio should slightly increase with temperature (see e.g. Ref.…”

Section: Linear Lennard-jones Chainsmentioning

confidence: 99%

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Liquid-crystal phase equilibria of Lennard-Jones chains

2016

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Liquid-crystal phase equilibria of Lennard-Jones chain fluids and the solubility of a Lennard-Jones gas in the coexisting phases are calculated from Monte Carlo simulations. Direct phase equilibria calculations are performed using an expanded formulation of the Gibbs ensemble. Monomer densities, order parameters, and equilibrium pressures are reported for the coexisting isotropic and nematic phases of: (1) linear Lennard-Jones chains, (2) a partially-flexible Lennard-Jones chain, and (3) a binary mixture of linear Lennard-Jones chains. The effect of chain length is determined by calculating the isotropic-nematic coexistence of linear Lennard-Jones chain fluids made of 8, 10, and 12 segments (8-, 10-, 12-mer). The effect of molecular flexibility on the isotropic-nematic equilibrium is studied for a Lennard-Jones 10-mer chain fluid with one freely-jointed segment at the end of the chain. An isotropic-nematic phase split and fractionation are reported for a binary mixture of linear 7-mer and 12-mer chains. Simulation results are compared with theoretical results as obtained from a recently developed analytical equation of state based on perturbation theory. Excellent agreement between theory and simulations is observed. The solubility of a monomer Lennard-Jones gas in the coexisting isotropic and nematic phases is estimated using the Widom test-particle insertion method. A linear relationship between solubility difference and density difference at isotropic-nematic coexistence is observed. It is shown that gas solubility is independent of the nematic ordering of the fluid, at constant temperature and density conditions.

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Section: Resultsmentioning

confidence: 99%

Section: Linear Lennard-jones Chainsmentioning

confidence: 99%

Liquid-crystal phase equilibria of Lennard-Jones chains

2016

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“…31 In the present work, the isotropic contributionã pert iso of Eq. (24) is calculated from this EoS.…”

Section: Isotropic Contributionmentioning

confidence: 99%

“…As shown in Ref. 31, the resulting EoS leads to an accurate representation of the vapor-liquid equilibrium (VLE) of fully flexible LJ chain fluids. Moreover, the above equations can be used as a reasonable approximation for the perturbation contributions of rigid linear and partially flexible chain fluids.…”

Section: Isotropic Contributionmentioning

confidence: 99%

“…Since the properties of the soft repulsive reference fluid that results from this decomposition are quite difficult to obtain, it is common to map its properties onto those of a hard repulsive reference fluid with an effective segment size d. In the original recipe of BH, this effective segment size involved a temperature dependence only. In a recent work, 31 however, we showed that the additional density-and chain-length dependence of the effective segment diameter need to be considered to arrive at a sufficiently accurate description of a BH repulsive fluid. Accordingly, we calculate the effective segment size d from the following equation:…”

Section: A Equation Of Statementioning

confidence: 99%

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An analytical equation of state for describing isotropic-nematic phase equilibria of Lennard-Jones chain fluids with variable degree of molecular flexibility

Westen

Oyarzún

Vlugt

et al. 2015

The Journal of Chemical Physics

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Articles you may be interested inWe develop an equation of state (EoS) for describing isotropic-nematic (IN) phase equilibria of Lennard-Jones (LJ) chain fluids. The EoS is developed by applying a second order Barker-Henderson perturbation theory to a reference fluid of hard chain molecules. The chain molecules consist of tangentially bonded spherical segments and are allowed to be fully flexible, partially flexible (rodcoil), or rigid linear. The hard-chain reference contribution to the EoS is obtained from a Vega-Lago rescaled Onsager theory. For the description of the (attractive) dispersion interactions between molecules, we adopt a segment-segment approach. We show that the perturbation contribution for describing these interactions can be divided into an "isotropic" part, which depends only implicitly on orientational ordering of molecules (through density), and an "anisotropic" part, for which an explicit dependence on orientational ordering is included (through an expansion in the nematic order parameter). The perturbation theory is used to study the effect of chain length, molecular flexibility, and attractive interactions on IN phase equilibria of pure LJ chain fluids. Theoretical results for the IN phase equilibrium of rigid linear LJ 10-mers are compared to results obtained from Monte Carlo simulations in the isobaric-isothermal (N PT) ensemble, and an expanded formulation of the Gibbs-ensemble. Our results show that the anisotropic contribution to the dispersion attractions is irrelevant for LJ chain fluids. Using the isotropic (density-dependent) contribution only (i.e., using a zeroth order expansion of the attractive Helmholtz energy contribution in the nematic order parameter), excellent agreement between theory and simulations is observed. These results suggest that an EoS contribution for describing the attractive part of the dispersion interactions in real LCs can be obtained from conventional theoretical approaches designed for isotropic fluids, such as a Perturbed-Chain Statistical Associating Fluid Theory approach. C 2015 AIP Publishing LLC.[http://dx

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Phase Behavior of Lyotropic Liquid-Crystalline Polymers under Varying Solvent Conditions: Effect of External Fields on the Phase Diagram

Егоров

2021

J. Phys. Chem. B

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In this work, we report a Density Functional Theory based study of phase behavior of lyotropic liquid-crystalline polymers under both good and varying solvent conditions in the presence of external electric or magnetic field. Our microscopic model for the good solvent case is based on the tangent hard-sphere chain with bond-bending potential to account for the chain stiffness; the variable solvent quality is modeled by adding attractive monomer–monomer interactions. The phase diagrams are constructed in three intensive variables (temperature, pressure, and field strength), and are characterized by the presence of critical and triple lines, which originate from the critical and triple points of the corresponding zero-field case. The merging of critical and triple lines results in the appearance of the “double critical” and “critical triple” points, already known from the earlier studies of the phase behavior of spin fluids in magnetic fields. The important difference of the present model from the spin fluids is due to the finite stiffness of the polymer chains (characterized by their persistence length), which adds an additional parameter controlling the morphology of the phase diagrams.

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On the vapor-liquid equilibrium of attractive chain fluids with variable degree of molecular flexibility

Cited by 6 publications

References 87 publications

Liquid-crystal phase equilibria of Lennard-Jones chains

Liquid-crystal phase equilibria of Lennard-Jones chains

An analytical equation of state for describing isotropic-nematic phase equilibria of Lennard-Jones chain fluids with variable degree of molecular flexibility

Phase Behavior of Lyotropic Liquid-Crystalline Polymers under Varying Solvent Conditions: Effect of External Fields on the Phase Diagram

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