Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 139).

This thesis is divided into two parts. In Part A the reference hypernetted-chain (RHNC) approximation is solved for a fluid of hard spheres with embedded point dipoles and linear quadrupoles. The thermodynamic properties, the dielectric constant, ∈, and the pair correlation function are compared with previously calculated Monte Carlo data as well as with results from other integral equation methods. The RHNC is found to closely approximate the Monte Carlo results and is shown to improve on the other methods. In Part B a self-consistent mean field theory for molecular polarizability is used, together with the RHNC approximation used in Part A, for a polarizable dipole-linear quadrupole fluid with ammonia-like parameters. The dielectric constant is calculated at three sub-critical temperatures and it is found to be quite sensitive to the quadrupole moment. Experimental results for ∈ are shown to be well within the uncertainty, set by the quadrupole moment, in the calculated ∈ values. These calculated ∈ values are shown to be significantly larger than the dielectric constants for the equivalent non-polarizable system. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

No description available.

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 170-178).

No description available.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 108-109). Also available in electronic version. Access restricted to campus users.

The statistical mechanics of the interfacial region is studied using the Monte Carlo and molecular dynamics simulation techniques. The penetrable-sphere model of the liquid/vapour interface is simulated using the Monte Carlo method. The pressure equation of state is calculated in the one-phase region and compared to analytic virial expansions of the system. Density profiles of the gas/liquid surface in the two-phase region are calculated and are compared to profiles solved in the mean-field approximation. The effect of the profile near a hard wall is investigated and as a consequence the theory is modified to account for a hard wall. The theory agrees well with the computer result. This is a simple model for adsorption of a gas at a solid surface. A model for methane adsorbed on graphite is proposed. A number of simplifying assumptions are made. The surface is assumed to be perfectly smooth and rigid, and quantum effects are neglected. An effective site-site pair potential for the methane-graphite interaction is adjusted to fit the rotational barriers at OK. The isosteric enthalpy at zero coverage is predicted in the range OK to 200K, by averaging the configurational energy during a molecular dynamics simulation of one methane molecule. The surface second virial coefficients are calculated in the range 225K to 300K and agree with the experimental measurements. The effective pairwise potential predicts the height of the monolayer above the surface and the vibrational frequency against the surface. The translational and rotational behaviour of a single methane molecule are examined. Solid √3 x √3 epitaxial methane is studied at a constant coverage of θ = 0.87 by molecular dynamics simulation. The specific heat and configurational energy are monitored. A slow phase transition occurs between OK and 30K and a sharp transition is observed at 90K. Calculation of the centre-centre distribution functions and order parameters indicates the first transition is due to a slow rotational phase change. At 90K some molecules evaporate from the surface and the remaining bound molecules relax into a 2-d liquid. Between 10K and 25K the adsorbed methane floats across the surface and the question remains open whether this phenomenon is an artifact of the model system or does occur in nature. The dynamical behaviour of adsorbed methane is compared to incoherent inelastic neutron scattering. The principal peaks in the self part of the incoherent structure factor S_s (0,_ω) should correspond to the peaks in the Fourier transforms of the velocity and angular velocity auto-correlation functions. The peaks calculated from the Fourier transform of the auto-correlation functions agree with all the assignments in the experiments. The reorientational motion in the monolayer is monitored and the reorientational auto-correlation functions characterize the slow phase transition from UK to 30K. Three methane molecules are scattered on top of the θ = 0.87 monolayer at 30K. Reorientational correlation functions are compared for the single adsorbed molecule, the monolayer and a few particles in the bilayer. Rotation is less hindered in the monolayer than for a single adsorbed molecule and least hindered in the second layer. Adsorbed methane is studied at coverages of θ < 0.87 over a wide range of temperature in order to unravel various conflicting solid and liquid phases predicted by experiment. By careful monitoring of the structure via changes in the specific heat, the distribution functions and order parameters a liquid/gas coexistence is not observed in the region 56K to 75K. This result is confirmed by calculating the self diffusion coefficients over two isotherms at 65K and 95K. The diffusion coefficients decrease with increasing coverage over both isotherms. If liquid and gas coexist the diffusion coefficient should not change with increasing coverage. The statistical mechanical expression for the spreading pressure of an adsorbed fluid is derived and reported over a wide range of temperature and coverage. Experimental techniques are not as yet sufficiently highly developed to measure this quantity directly. An expression for the coherent neutron scattering structure factor for a model of liquid benzene adsorbed on graphite is derived. This expression is a function of the 2-dimensional centre-centre distribution function and we solve the Ornstein-Zernike equation in the Percus-Yevick approximation to obtain the 2-d distribution functions for hard discs. Agreement with present experimental results is reasonable, but a more highly orientated substrate needs to be used in experiment before a more exact comparison can be made.

Boltzmann's equation for binary chemical reactions has been solved by the modified moment method using the equivalent of the 13-moment approximations. It was found that the transport coefficients are nonlinear in the thermodynamic forces. This nonlinearity is at least quadratic. The rate coefficient also appears to be at least quadratic in fluxes. / The stability of the solutions of two coupled equations of change for the current under the influence of an electric field is examined. These equations are deduced from the structure of dissipative terms calculated in the modified moment method. Two steady state branches in current are found to bifurcate from the primary steady state branch as a critical field value E(,c) = 4.35 V/cm is crossed. The results are in good qualitative agreement with experiment. / The dynamical behaviour of the two coupled equations used above was also studied in order to establish the influence (if any) of the entropy production surface on the trajectory followed by the system. This aspect of the study proved to be difficult since the entropy production surface associated with the two equations used did not have sufficiently distinctive features. / In order to continue studies on the relationship between dynamical behaviour and the topography of the entropy production surface, the two basic equations used before were slightly modified, and new parameters were introduced. At the critical field value E(,c) = 1.48 V/cm, no secondary steady states bifurcated out of the unstable primary steady state as in the previous model. Rather, stable oscillations in current of more or less constant amplitude occurred. This may account for some of the current fluctuations observed in experiment. The entropy production surface associated with this pair of model equations consists of two intersecting locii of minima. It turns out that the trajectory follows these minimal regions for most of the orbit, crossing from one locus of minima to another either through the intersection near to the origin or by crossing a ridge of high entropy production. The average energy dissipated over this cycle turns out to be smaller than if the system had remained with the unstable steady state. / Out of the latter studies, the useful conjecture was made. Given the topography of the entropy production surface and the stability of the steady states, it is possible to qualitatively predict the dynamics of the system provided the entropy production surface has sufficiently distinctive features.

No description available.