Barus effect in polymer flows through cylindrical and flat dies

The determination of the swell factor of a polymer jet extruded from a cylindrical or flat die is examined. Relations are obtained for the dependence of the swell factor on shear rate and shear stress, expressed in terms of the constants of the rheological model.Scientific Research Institute of Plastics, Moscow. Kiev Polytechnic Institute. Translated from Mekhanika Polimerov, No. 3, pp. 487–492, May–June, 1976.     

Newtonian viscosity of polymer solutions over a wide range of compositions as a function of certain parameters determining it

Using solutions of various polymers in a large number of solvents as an example, the possibility of constructing a generalized characteristic for their viscosity, which is invariant relative to the molecular weight of the polymer and the nature of the solvent, is indicated. It is shown that the parameters characterizing the properties of individual macromolecular chains are the dimensions of the coils [], and the rheological effectiveness of interaction of the segments K_M retain their importance and quantities determining the viscous properties of the polymer solution over the whole range of compositions. A connection is established between the datum parameter K_M and the thermodynamic properties of dilute solutions of polymers, the flexibility of the polymer chain, and the energy of its intermolecular interaction.A. M. Gor'kii, Ural State University, Sverdlovsk. A. V. Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1110–1117, November–December, 1972.     

Rheological properties of anisotropic poly(para-benzamide) solutions

A study has been made of the viscous properties of poly(para-benzamide) (PBA) solutions in dimethyl acetamide, which undergo a transition from an isotopic to an anisotropic (liquid-crystal) state at a definite concentration C^*. The polymer solutions behave in many respects (as regards the concentration and temperature dependence of viscosity, etc.) like solutions of low molecular weight compounds forming a liquid crystal phase, although the transitions are less pronounced in the polymer solutions owing to their polydispersity. It is shown that the viscometric method, being extremely sensitive to C^*, is convenient for determining phase diagrams of anisotropic polymer solutions. The values of C^* as related to the molecular weight of PBA have been determined, and a general criterion for transition from isotropic to anisotropic solutions established; the latter has the form (CM?)^* ≈ 1.3 × 10⁵ at 20°C. This criterion is in line with the condition for the formation of the liquid-crystal structure in a dispersion of rodlike particles as proposed by Flory. Generalized concentration dependences of viscosity have been plotted by reducing concentration to C^* and viscosity, to the maximum viscosity at the phase transition point. In investigating the flow properties of PBA solutions we revealed the existence of a yield point in the range of low shear stresses, and an intersection of the flow curves of solutions of different concentration at high shear stresses, which excludes a generalized representation of the flow curves in reduced ordinary-type coordinates.     

Photochemistry of molecular systems for optical 3D storage memory

The photochemistry, kinetics and spectra of several spiropyran molecules have been studied. The transient species of the photochromic reactions and precursors have been identified and the rate of formation and decay measured. We also present means for the utilization of spiropyrans in writing and accessing information in 3D volume optical memory.     

Enhanced superhyperfine structure of the EPR spectra of a U<Superscript>3+</Superscript> ion introduced into the Van Vleck paramagnet LiTmF<Subscript>4</Subscript>

The observation of the superhyperfine structure (SHFS) in EPR spectra due to enhanced nuclear magnetism is reported. The X-band spectrum of a U³⁺ ion introduced into the Van Vleck paramagnet LiTmF₄ is measured in the temperature range of 5–20 K and compared with the spectra of LiLuF₄:U³⁺ and LiYF₄:U³⁺ single crystals. The spectra reveal well-resolved and strikingly different SHFS. The SHFS of Li(Lu, Y)F₄:U³⁺ is due to the fluorine ions forming the nearest surroundings of the U³⁺ ion. The main contribution to the SHFS of the U³⁺ spectrum in LiTmF₄ comes from the Tm³⁺ ions with a highly enhanced nuclear gyromagnetic tensor. The text was submitted by the authors in English.