Solution Of Rodlike Macromolecules Research Articles

Depletion interactions induced by flexible polymers in solutions of rod-like macromolecules

An analytic integral equation treatment is developed for the entropic depletion attractions induced by flexible polymers in dilute solutions of rigid rod-like macromolecules. The polymer-induced changes in the pair correlation functions between rod-like molecules and the rod–rod second virial coefficient are compared with results derived from a scaling approach. Results from both approaches predict that, for flexible coil-like depletants with radii of gyration sufficiently large compared to the rod lengths, the rod–rod second virial coefficient shows a nonmonotonic dependence on the coil concentration with a minimum located near the semidilute threshold. Our results are analogous to prior findings for athermal mixtures of flexible coils and hard spheres, and the predicted nonmonotonicities in the second virial coefficients between dispersed particles have the same physical origins.

Phase transitions in a solution of rodlike macromolecules of two different sizes

Phase equilibria for a solution of long rigid rods of diameters Di and lengths Li (i = 1,2) are studied analytically using Gaussian trial functions. The conditions on the molecular size parameters for a nematic—nematic phase transition to be possible are determined, and found to be satisfied everywhere except in a closed domain in the diameter ratio—length ratio plane. Information on the relative ordering of the two components is also provided.

Polydispersity and ordered phases in solutions of rodlike macromolecules.

We apply density functional theory to study the influence of polydispersity on the stability of columnar, smectic and solid ordering in the solutions of rodlike macromolecules. For sufficiently large length polydispersity (standard deviation $\sigma>0.25$) a direct first-order nematic-columnar transition is found, while for smaller $\sigma$ there is a continuous nematic-smectic and first-order smectic-columnar transition. For increasing polydispersity the columnar structure is stabilized with respect to solid perturbations. The length distribution of macromolecules changes neither at the nematic-smectic nor at the nematic-columnar transition, but it does change at the smectic-columnar phase transition. We also study the phase behaviour of binary mixtures, in which the nematic-smectic transition is again found to be continuous. Demixing according to rod length in the smectic phase is always preempted by transitions to solid or columnar ordering.

Analysis of Depolarized Light Scattering from a Solution of Rod-Like Macromolecules Through A Laplace Transform Method

Abstract In this work, an analysis is made of the depolarized component of the light scattered by a solution of rod-like macromolecules by measuring the Laplace Transform (LT) of the time interval probability between successive photoelectrons, P(t). The study was performed in forward scattering conditions, which allows direct evaluation of the Rotational Diffusion Coefficient, Dr. Results were obtained by means of computer simulation and are compared with those obtained through the measurement of the second order correlation function, g(2)(τ), for the same experimental conditions.

Light scattering from liquid crystalline solutions of rod-like macromolecules

Light scattering from liquid crystalline solutions of rod-like macromolecules

Toward Monodisperse Poly(γ–benzyl α,L-glutamate): Uniform, Polar, Molecular Rods

Poly(γ-benzyl α,L-glutamate) (PBLG) has been widely used in studies of the physics of rod-like polymer chains [1]. The helical structure of PBLG gives rise to considerable chain stiffness, such that the persistence length of the chain is on the order of 70 nm in helicogenic solvents [2]. This feature, coupled with the ease of synthesis and good solubility of the polymer has made PBLG the system of choice for the study of both isotropic [2,3] and liquid crystalline [4] solutions of rod-like macromolecules.

The phase behaviour and gelation of a rod-like polymer in solution and implications for microcellular foam morphology

The phase separation and gelation of the rod-like macromolecule, poly(γ-benzyl- l-glutamate), were studied in an effort to understand the mechanism by which microcellular materials are made via thermally induced phase separation processes. Previous workers have studied similarly prepared materials from molecules which exist as random coils in solution. The microcellular materials were formed by lowering the solution temperature until phase separation and solvent freezing occurred. The solvent was removed by vacuum sublimation. An emphasis was placed on dilute isotropic solutions (<5 wt%) which yield low-density materials or ‘foams’. Both one- (e.g. benzene) and two-component (e.g. dioxane/water) solvent systems were employed. The morphology produced by liquid-liquid phase separation and gelation was an open-celled, fibrous structure, which resembles a three-dimensional lattice. The cell diameters were in the range of 1–10 μm and the fibres which comprise the struts were 0.2 to 2.0 μm thick. Various experimental observations are discussed in terms of the theories and proposed mechanisms of phase separation in solutions of rod-like macromolecules. Calculations of the spinodal for the Flory theory of rod-like particles were also made to assess the possibility of placing the isotropic solutions into an unstable region.

Rheology of dilute solutions of rod-like macromolecules

The rheological properties of dilute solutions of rod-like macromolecules are treated on the basis of a new model of macroparticle dynamics. Calculations are presented of the rigidity modulus, the shear viscosity, and the first and second normal stresses.

Screening of hydrodynamic interaction in a solution of rodlike macromolecules

Influence de la concentration de la solution. Resultats inverses de ceux pour une solution de chaines flexibles

Note on the Normal Stress Effect in the Solution of Rodlike Macromolecules

Three components of normal stresses in a solution of rodlike macromolecules are calculated on the basis of the general theory of irreversible processes of macromolecular solutions developed by Kirkwood. The results are expressed in expansion series of even powers of the rate of shear and are explicitly given to their fourth powers. When the hydrodynamic interaction is not taken into account, two components of the normal stresses perpendicular to the direction of flow identically vanish, while, by the introduction of this interaction, they appear. The action of normal stresses is still mainly ``pull'' in the direction of flow as in the free-draining case.