Rigid Rod-like 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.

Time-resolved small-angle X-ray scattering and wide-angle X-ray diffraction studies on the nanostructure of melt-processable molecular composites

Novel melt-processable molecular composites were obtained from isotactic polypropylene (iPP) and liquid-crystalline oligoester (LCO). The nanostructure and thermal behaviour of molecular composites were examined by real-time synchrotron small-angle X-ray scattering and wide-angle X-ray diffraction methods, and differential scanning calorimetry. The synthesized oligoester, with low melting temperature (391 K), exhibits the ability to form a thermotropic mesophase. It was shown that strong rigid rod-like macromolecules of LCO are dispersed at the molecular scale in iPP matrix and act as reinforcing fibres.

The fractal nature of 1-step highly-branched rigid rodlike macromolecules and their gelled-network progenies

Highly branched aromatic polyamides characterized by stiff trifunctional branchpoints connected by rigid rodlike segment are prepared by one-step polycondensation and studied in their pregell and postgel states. It is shown that the nature of the growing one-step rigid aggregates in the pregel state is consistent with the fractal model and that because of of the branchpoint and segmental rigidity and the rather large average length of the segments between branch-points, the rigid one. Step fractals are remarkably porous on the scale of the solvent molecules

A new mechanism of ultrasonic absorption in aqueous solutions of rigid macromolecules

The temperature- and frequency-dependences of the ultrasonic absorption in lyotropic liquid crystals of rod-like FD virus particles have been measured with the ultrasonic beam being parallel or perpendicular to the rod axis. The experimental results show a strongly anisotropic ultrasonic absorption in the lyotropic liquid crystals, which varies with temperature exactly as the shear viscosity of water. Experimental results are in good agreement with the following model for the absorption process. The authors believe that the absorption arises from differential flow of water between the relatively long and rigid rod-like macromolecules. This mechanism of ultrasonic absorption becomes dominant for frequencies of 1-100 MHz. The validity of this mechanism is, however, not restricted to the special lyotropic crystals discussed here. Instead, this absorption process is expected to be important also for other macromolecular solutions whenever the dissolved macromolecular objects have a sufficiently large linear dimension in the direction parallel to the sound beam.

Multiple-time scale approach to stress growth in suspensions of rodlike macromolecules

The rheologial properties of a dilute suspension of rigid rodlike macromolecules at the inception of a steady homogeneous flow are examined within the framework of the kinetic theory of polymeric liquids. The cases of simple shear and elongational flows are considered under the assumption of small non-dimensional shear rates, ϵ = κ 0/6 D, where D is the rotation diffusion of the particles. The method of multiple-time scales is used to solve the problem and the resulting transport coefficients are shown to reveal new features as compared with the results of the straightforward perturbation technique. In particular, the onset of stress oscillations leading to an undershoot following the overshoot of the shear viscosity and the overshoot of the normal stress difference are detected as ϵ approaches unity.

On the kinetic theory and rheology of a solution of rigid-rodlike macromolecules

On the kinetic theory and rheology of a solution of rigid-rodlike macromolecules

Kinetic theory and rheology of solutions of rigid rodlike macromolecules

It is known that the second normal-stress coefficient Ψ 2 is quite sensitive to molecular structure. Here Ψ 2 is tudied for suspensions of rigid rodlike molecules, which are modeled as rigid multibead rods with hydrodynamic interaction described by the Rotne-Prager-Yamakawa hydrodynamic-interaction tensor. It is shwon that Ψ 2 is positive for N ⩽ 6 and negative for N ⩾ 7 for rods made up of osculating spheres. Results are also given for the viscosity η, the first normal-stress coefficient Ψ 1, and the elongational viscosity, −η. The first two terms of the corotationnal memory-inegral expansion are given explicitly, and the effective-velocity-gradient method for accounting for hydrodynamic interaction is discussed.

Orientational effect of the extensional flow field on solutions of rigid rodlike macromolecules-disappearance of the isotropic to nematic phase transition

The effect of steady state uniaxial extensional flow on a solution of rigid rodlike macromolecules is theoretically studied. The mean field theory of Maier and Saupe is extended to cover situations in which the macromolocular solution is subjected to an extensional flow field. It is found that for a given solution a critical flow gradient exists beyond which the first order nematic-isotropic phase transition, which is typical of such solutions in the absence of flow, disappears. A similar result is obtained when the theory of Onsager is applied to the problem. Order parameter as a function of flow gradient is calculated and it is shown that the contribution of flow to the ordering of macromolecules is most significant when the stationary solution is isotropic but close to the transition point.

Viscosity of Solutions of Rigid Rodlike Macromolecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTViscosity of Solutions of Rigid Rodlike MacromoleculesR. R. Matheson Jr.Cite this: Macromolecules 1980, 13, 3, 643–648Publication Date (Print):May 1, 1980Publication History Published online1 May 2002Published inissue 1 May 1980https://doi.org/10.1021/ma60075a030RIGHTS & PERMISSIONSArticle Views204Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (821 KB) Get e-Alerts Get e-Alerts

Theory of Chromatography of Rigid Rod-Like Macromolecules on Hydroxyapatite Columns: VIII. Further Theory of Analytical Calculation of Chromatograms and Further Investigations on the Resolving Power of the Columns

Theoretical chromatograms for mixtures of rigid rod-like macromolecules with the same dimensions and the same shape but with different adsorption energies have been calculated analytically for the case when the slope of the linear gradient of the competing ion is small enough. Account has been taken of the fact that the number, x', of sites of hydroxyapatite covered by an adsorbed molecule has a finite value. In Part VII of this series, it was shown that high resolutions can generally be obtained by using a small slope of the gradient. In this paper, we show that the resolving power of the column cannot be improved further if the slope of the gradient of the competing ion is already small enough.

Theory of chromatography of rigid rod-like macromolecules on hydroxyapatite columns : VII. Investigations on the resolving power of the columns

The resolving powers of hydroxyapatite columns for several types of mixtures of rigid rod-like model molecules with different values of the adsorption energies and lengths obtained under different chromatographic conditions have been investigated theoretically. It has been shown that, when the properties of different molecules are similar, high resolutions can generally be obtained by using a small slope of the gradient of competing ions and short columns (or high loads). High resolutions can also be obtained when the activity of competing ions in the initial buffer is sufficiently small. When both the molecular length and the adsorption energy per unit molecular length are not constant, the order of elution of different molecules depends on the chromatographic conditions. When all molecules have the same length, the resolution increases with increase in molecular length.

Steric hindrance in macromolecular solutions

AbstractThe same point in the space cannot be occupied simultaneously by two molecules. In a solution of rigid rodlike macromolecules, each molecule prevents its neighbors from occupying certain positions, the whole of which form the forbidden angle. Calculation shows that in the case of rigid, filiform molecules, this angle is large even at very low concentrations. Isotropy is not possible at moderate concentrations. The consideration of the forbidden angle is necessary in the study of viscosity, osmotic pressure, flow birefringence, sedimentation, and molecular light scattering. In the solid state, the substance can be put under great tension, and the return to the normal state is extremely slow. This tension accounts for the abnormal solubility of disordered high polymers.