J. Stecki

Statistical theory of the elastic constants of nematic liquid crystals

A statistical mechanical theory of the Frank elastic constants is formulated. The free energy functional is constructed for the deformed sample and the free energy density is defined for the case of small spatial gradients. The Frank constants are expressed in terms of the direct correlation function c(1, 2) and the orientational single particle distribution function. For the example of Onsager spherocylinders three constants K 1, K 2 and K 3 are calculated. The results of these calculations are similar to those given by Priest and by Straley.

Vapour pressures and thermodynamic properties of hexan-1-ol + n-hexane between 298.230 and 342.824 K

Abstract Vapour pressures of dodecan-1-ol + n -hexane have been measured between 298.230 and 342.824 K at 10 temperatures at about 5 K intervals by a precision static method. The excess functions G E , H E , and TS E were calculated and compared with those previously reported for hexan-1-ol + n -hexane.

Density profiles at a planar liquid‐liquid interface

Molecular dynamics of liquid‐liquid interface in an immiscible binary mixture of simple particles at low temperature and high pressure reveals stable equilibrium oscillatory structures in the density profiles of both components. The layering vanishes albeit slowly with the increase of the surface area but is not affected by an increase of the depths of bulk liquid layers. A simple Gaussian broadening predicts scaling of the oscillatory portion of the density profiles and good agreement is found. The width of the dip in the total density is also examined.

Heat capacities of liquids at temperatures between 90 and 300 K and at atmospheric pressure I. Method and apparatus, and the heat capacities of n-heptane, n-hexane, and n-propanol☆

Abstract A semi-automatic adiabatic calorimeter based on the Westrum descriptions (4) has been constructed to measure heat capacities of pure liquids and liquid mixtures in the temperature range 90 to 300 K. The heat capacity of the empty calorimeter and the molar heat capacities of C 7 H 16 and C 6 H 14 were determined. Excellent agreement with the results of Ginnings and Furukawa was found for heptane. The molar heat capacity of C 3 H 7 OH was measured. The temperature range was in all cases 180 to 300 K.

Application of the statistical theory of elastic constants of nematics to spherocylindrical molecules with attractive forces

The statistical theory of the elastic constants of nematic liquid crystals is applied to detailed calculations based on well-defined approximations for the direct correlation function of Ornstein and Zernike and for the singlet orientational distribution. The model of hard spherocylinders with superimposed r -6 attraction modulated by a Maier-Saupe P 2(cos ϑ1 2) term, is used. The dependence on temperature, on the order parameter and on the length to breadth ratio, of the reduced elastic constants K* i (i=1, 2, 3), is discussed in some detail and comparison with experiment is included.

SHEAR FLOW AT LIQUID-LIQUID INTERFACES

Two nonmiscible liquids separated by planar interfaces and undergoing shear flow have been simulated with nonequilibrium molecular dynamics (NEMD) methods. A homogeneous shear scheme was used for imposing shear flow in the system. The homogeneous shear algorithm needs to be combined with a profile‐unbiased thermostat (PUT) in order to assure meaningful results in our nonhomogenous system. Local values of several quantities such as viscosity, local stream velocity, temperature, shear stress, and rate of entropy production were calculated. Planar Couette flow appears in the ‘‘bulk’’ regions of the system with a slip between the two streams of bulk fluid at the interfaces. The shear stress is constant across the system (PUT results) at low strain rates but at high shear rates the shear stress at the interface is lower than in the bulk region. The shear viscosity at the interfaces is lower than in the bulk region showing that the transport of momentum in the former region is less efficient than in the bulk. A...

On the stability of the isotropic phase towards nematic and smectic A formation

A new stability condition governing the formation of liquid crystalline phases of various degrees of orientational or translational ordering and supplementing the standard conditions of mechanical or thermal stability of a phase, is applied to the specific example of formation of a smectic A or a nematic phase from an isotropic phase. Numerical results are shown for a molecular model of hard spherocylinders with an r -6 centre-to-centre attraction. Such molecules should form smectic A phases and the smectic range for which the stability breaks first, is of reasonable order of magnitude. The effect of temperature and the length of the molecule is examined.

Extended capillary wave theory and the ellipsometric coefficient

The extended capillary wave theory (ECW) proposed by Robledo et al. and formulated in terms of the unknown direct correlation function C of the two-phase system with a planar interface between liquid and its vapor, is applied to our simulation data on the full inhomogeneous two-point correlation function H from which C is also obtained. The required projection, C(q), is shown and discussed. The coefficient of q4, the apparent bending coefficient, was inequivocally negative, in agreement with the view that the true bending coefficient may be absent in one-component interfaces. The ellipsometric coefficient diverged and its calculation still required an ultraviolet cutoff. It is thus demonstrated that ECW is but the first step and further terms, some discovered earlier, as well as mode–mode coupling, are required. These are discussed.

Hard sphere cavity in a liquid‐density functional approach

The system of particles, interacting via a reasonably realistic intermolecular potential, in contact with a hard spherical wall is studied. The weighted density approximation is used to determine the density distribution and the liquid–wall surface tension. The effect of the wall curvature on the density at contact and the surface tension is investigated. The predictions of the model calculations are compared with the results of the computer simulations and a qualitative agreement is found. It is suggested that the asymptotic expansion of the surface tension and the density at contact in powers of the curvature may not be valid for cavities of microscopic size.

Heat capacities of liquids in the temperature interval between 90 and 300 K and at atmospheric pressure II. Heat capacities and excess heat capacities of propan-1-ol +n-heptane and +n-hexane☆

Molar heat capacities Cp of xC3H7OH + (1 − x)C7H16 and +(1 − x)C6H14 were measured in an adiabatic calorimeter for the whole range of x and at temperatures from 185 to 300 K. Excess heat capacities CpE were derived from these results and from the heat capacities of the pure components. New features of the curves of CpE against x have been observed at moderately low x, notably a shoulder at high temperatures developing into a new minimum at low temperatures in both systems.