The influence of the extent of excluded volume interactions on the linear viscoelastic properties of dilute polymer solutions

The Rouse model has recently been modified to take into account the excluded volume interactions that exist between various parts of a polymer chain by incorporating a narrow Gaussian repulsive potential between pairs of beads on the Rouse chain (cond-mat/0002448). The narrow Gaussian potential is characterized by two parameters: z* - which accounts for the strength of the interaction, and d* - which accounts for the extent of the interaction. In the limit of d* going to zero, the narrow Gaussian potential tends to the more commonly used delta-function repulsive potential. The influence of the parameter d*, in the limit of infinite chain length, on equilibrium and linear viscoelastic properties, and on universal ratios involving these properties, is examined here. A renormalization group calculation of the end-to-end vector suggests that the value chosen for the variable d* will not affect critical exponents, or universal ratios. A similar trend is also observed for results obtained with an approximate solution, which is based on the assumption that the non-equilibrium configurational distribution function is Gaussian.Comment: 23 pages, 6 figures, LaTe

The Kinetic Theory of Dilute Solutions of Flexible Polymers: Hydrodynamic Interaction

The development of a coherent conceptual basis for the treatment of non-linear microscopic phenomena, such as, hydrodynamic interaction, finite extensibility, excluded volume and internal viscosity, in molecular theories of dilute polymer solutions, is discussed. In particular, recent advances in the treatment of hydrodynamic interaction are reviewed, and the successive refinements which have ultimately led to the prediction of universal viscometric functions in theta solvents are highlighted.Comment: 31 pages, 1 figure, latex, To appear in: Advances in the Flow and Rheology of Non-Newtonian Fluids, D. A. Siginer, D. D. Kee, R. P Chabra, eds., Elsevier Science, 199

Viscoelastic fluid flow in a 2D channel bounded above by a deformable finite thickness elastic wall

The steady flow of three viscoelastic fluids (Oldroyd-B, FENE-P, and Owens model for blood) in a two-dimensional channel, partly bound by a deformable, finite thickness neo-Hookean solid, is computed. The limiting Weissenberg number beyond which computations fail to converge is found to increase with increasing dimensionless solid elasticity parameter {\Gamma}, following the trend Owens > FENE- P > Oldroyd-B. The highly shear thinning nature of Owens model leads to the elastic solid always collapsing into the channel, for the wide range of values of {\Gamma} considered here. In the case of the FENE-P and Oldroyd-B models, however, the fluid-solid interface can be either within the channel, or bulge outwards, depending on the value of {\Gamma}. This behaviour differs considerably from predictions of earlier models that treat the deformable solid as a zero-thickness membrane, in which case the membrane always lies within the channel. The capacity of the solid wall to support both pressure and shear stress, in contrast to the zero-thickness membrane that only responds to pressure, is responsible for the observed difference. Compar- ison of the stress and velocity fields in the channel for the three viscoelastic fluids, with the predictions for a Newtonian fluid, reveals that shear thinning rather than elasticity is the key source of the observed differences in behaviour.Comment: 32 pages, 17 figures, accepted for publication in J. Non-Newton. Fluid Mec

Degree of Polarization in Quantum Optics through second generalization of Intensity

Classical definition of degree of polarization is expressed in quantum domain by replacing intensities through quantum mechanical average values of relevant number operators and is viewed as first generalization of Intensity. This definition assigns inaccurately the unpolarized status to some typical optical fields such as amplitude coherent phase randomized and hidden polarized, which are not truly unpolarized light. The apparent paradoxical trait is circumvented by proposing a new definition of degree of polarization in Quantum Optics through second generalization of Intensity. The correspondence of new degree of polarization to usual degree of polarization in Quantum Optics is established. It is seen that the two definitions disagree significantly for intense optical fields but coincides for weak light (thermal light) or for optical fields in which occupancy of photons in orthogonal mode is very feeble. Our proposed definition of degree of polarization, similar to other proposals in literature, reveals an interesting feature that states of polarization of optical quantum fields depend upon the average photons (intensity) present therein.Comment: 17 pages, Accepted in PR