Studies Of Orientational Order Of Some Nematogens By Means Of Raman Scattering Spectroscopy

The orientational behaviour of some liquid crystals with various molecular structures was studied by means of the Raman scattering depolarization method. The Raman scattering spectra of linearly polarized light were recorded as a function of temperature in the nematic phase. On the basis of these spectra the order parameters 〈P2〉 and 〈P4〉 as well as the molecular distribution function were determined. The obtained data were compared with those estimated on the basis of polarized light absorption and emission measurements. The influence of the molecular structure on the orientational order of liquid crystals was discussed.

Theory of Boundary Conditions for the Boltzmann Equation

In preceding papers, Refs. 1,2, boundary conditions were developed for transport-relaxation equations by aid of a general reciprocity postulate for the interface. The same method is now used for the linearized Boltzmann equation. A new scheme emerges: the kinetic boundary conditions consist in a linear functional relation between interfacial "forces and fluxes" - in the sense of non-equilibrium thermodynamics - which are, broadly speaking, given by the sum and the difference of the molecular distribution function and its time-reversed, at the wall. The general properties of the kernels occurring in this atomistic boundary law are studied. The phenomenological surface coefficients of (generalized) linear thermo-hydrodynamics, as e. g. temperature jump, slip coefficients etc., can in a simple way be expressed by the kernel of the atomistic boundary law. This kernel is explicitly worked out for completely thermalizing wall collisions.

Kinetic Theory for Mixtures of Dilute Gases of Linear Rotating Molecules II. The Senftleben-Beenakker Effect of the Heat Conductivity

The system of transport relaxation equations obtained from the linearized Waldmann-Snider equation is the starting point for the kinetic treatment of the heat conductivity for mixtures of linear diamagnetic molecules in an external homogeneous magnetic field. The connection of the occurring collision integrals with certain molecular cross sections is discussed and order of magnitude considerations are made for molecules with small nonsphericity of their interaction. With the Kagan polarization as the decisive rotational angular momentum anisotropy term in the molecular distribution function, an expression for the heat conductivity ini the presence of a magnetic field is derived for mixtures with an arbitrary number of components. The mole fraction dependence of the saturation values is studied for binary mixtures of rotating molecules and noble gas atoms for a simplified model. As an example, the system o-D2/He is considered.

Boundary-value problems in the kinetic theory of gases Part I. Slip flow

A new method for treating boundary-value problems in gas-kinetic theory has been developed. The new method has the advantage of reproducing the bulk or asymptotic flow properties accurately whilst giving a realistic description of the behaviour of the molecular distribution function in the neighbourhood of a wall. As an example, the Kramers, or slip-flow, problem is solved for a general specular-diffuse boundary condition and some new expressions for the slip coefficient, flow speed and molecular distribution function at the surface are derived.A brief discussion of the eigenvalue spectrum of the associated Boltzmann equation is given and its physical significance pointed out.Certain analogies between this problem and the Milne problem in neutron transport theory are demonstrated.

A note on Wild's solution of the Boltzmann equation

ABSTRACTIt is shown that Wild's formal solution of the Boltzmann integro-differential equation can be used to obtain Maxwell's classical relaxation behaviour of the second velocity moments of the molecular distribution function.