The phase behavior of linear and partially flexible hard-sphere chain fluids and the solubility of hard spheres in hard-sphere chain fluids

Abstract

The liquid crystal phase behavior of linear and partially flexible hard-sphere chain fluids and the solubility of hard spheres in hard-sphere chain fluids are studied by constant pressure Monte Carlo simulations. An extensive study on the phase behavior of linear fluids with a length of 7,8,9,10,11,12,13,14,15, and 20 beads is carried out. The phase behavior of partially flexible fluids with a total length of 8, 10, 14, and 15 beads and with different lengths for the linear part is also determined. A precise description of the reduced pressure and of the packing fraction change at the isotropicnematic coexistence was achieved by performing long simulation runs. For linear fluids, a maximum in the isotropic to nematic packing fraction change is observed for a chain length of 15 beads. The infinite dilution solubility of hard spheres in linear and partially flexible hard-sphere chain fluids is calculated by the Widom test-particle insertion method. To identify the effect of chain connectivity and molecular anisotropy on free volume, solubility is expressed relative to that of hard spheres in a hard sphere fluid at same packing fraction as relative Henry's law constants. A linear relationship between relative Henry's law constants and packing fraction is observed for all linear fluids. Furthermore, this linearity is independent of liquid crystal ordering and seems to be independent of chain length for linear chains of 10 beads and longer. The same linear relationship was observed for the solubility of hard spheres in nematic forming partially flexible fluids for packing fractions up to a value slightly higher than the nematic packing fraction at the isotropic-nematic coexistence. At higher packing fractions, the small flexibility of these fluids seems to improve solubility in comparison with the linear fluids. © 2013 AIP Publishing LLC. [http://dx

The isotropic-nematic phase transition of tangent hard-sphere chain fluids—Pure components

“…27. To show the effect of hysteresis around the phase transition, both the results from MC simulations started from an isotropic and a nematic initial configuration are included.…”

“…IV, theoretical predictions for the equation of state and nematic order parameter are extensively tested to MC simulations from literature. 27 We summarize our findings in Sec. V.…”

“…9, we show the density difference η at the phase transition and part of the phase diagram, respectively, of a 15-m R rod-coil. Compared to the MC data, 27 both SPT and the OVL-LHrc theory capture the general trends with respect to the rigidity parameter, i.e., for more flexible chains the phase transition is shifted to higher packing fraction and the density difference (relative to the isotropic coexistence density) is decreased. For all rod-coils shown, however, an overestimation of the density difference is observed.…”

“…A comparison of results obtained from SPT and the OVL-LHrc theory to the MC simulations from Ref. 27 (not included for brevity) showed that both theories are accurate down to a chain length of 9, resulting in an underestimation of the coexistence pressure, isotropic packing fraction, and nematic packing fraction of less than 7%, 5%, and 1%, respectively.…”

“…Typical model systems that have been studied in this respect, are hard discs, 14,15 rods, 16 cut spheres, 17,18 spherocylinders, 13,19 ellipsoids, 20,21 Gaussian overlap particles, 22 and hard-sphere chains. [23][24][25][26][27] Despite the simplicity of these molecular models, a rich phase behavior, involving isotropic (iso), nematic (nem), smectic, and columnar phases has been observed both by experiments 16 and by means of molecular simulations 13,17,20,27 and theory. 12,18,28 In the present work, the liquid crystalline state of interest is the nematic state.…”