General characteristics of the visco-elastic properties of flexible-chain polymer solutions over a wide range of concentrations

Summary The paper summarizes the ideas and results of investigations of viscous and high-elastic properties of polymer solutions in the whole interval of concentrations, chemical structure of the polymers used and the goodness of the solvents tried being varied in wide ranges.

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Zusammenfassung In diesem Beitrag sind die Ideen und experimentellen Resultate der Forschung von viscosen und hochelastischen Eigenschaften polymerer Lösungen im gesamten. Konzentrationsbereich zusammengestellt. Dabei wurden die chemische Struktur und Lösungsmittelqualität in weiten Grenzen variiert.

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With 20 figures     

Temperature-frequency reduction of the dynamic functions of black-filled rubbers in the nonlinear region

The possibility of using temperature-frequency reduction of the dynamic functions of black-filled rubbers in the nonlinear region is demonstrated and an additional applicability criterion — similar slopes of the isotherms of the amplitude dependences of the dynamic functions — is formulated. In the case of heavily filled rubbers it may be necessary to determine the constants of the Williams-Landel-Ferry equation and the reference temperature T_S from the experimental data — they may not coincide with the universal values. Master curves of the dynamic functions are obtained for a series of shock-absorbing rubbers at a shear strain amplitude =0.01.A. V. Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Scientific-Research Institute of the Rubber Industry, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 751–754, July–August, 1973.     

Ponderomotive effects in intense pumping wave action on electron and plasma bunches

Ponderomotive effects that arise when an intense plane pumping wave acts on low-concentration electron and plasma bunches are theoretically studied within the framework of a one-dimensional model. Using the Lagrange variables, an electron (plasma) bunch under the action of a pumping field can be represented as a gas comprising macroparticles with ponderomotive and Coulomb interactions. The ponderomotive force at small interparticle distances is attractive, that is, directed oppositely to the Coulomb force; it cannot, however, completely balance the latter. The constructed model is used to study superradiance, which arises when an intense pumping wave acts on an extended electron bunch. Radiation is then scattered in the form of narrow pulses whose amplitude is proportional to the total number of particles in the bunch. In addition, we describe acceleration of a neutral plasma layer, narrow on the wavelength scale, in the field of an intense wave and radiation field-induced partial contraction of an electron bunch with an incompletely compensated charge.     

Coherent states and asymptotic behavior of the symmetric top wave functions

Wave packets which may be considered as an analogue of the coherent states of the top are constructed. New integral representations are obtained for the D-function; making use of those, various types of the asymptotic behaviour of the D-function are obtained in the region of large quantum numbers.     

Viscoelastic properties and unstable flow of monodisperse polybutadiene solutions

The conditions governing the onset of unstable flow when concentrated solutions of monodisperse polybutadiene in -methylnaphthalene are extruded through a capillary have been investigated. The critical values of the parameters corresponding to these conditions have been found. It is shown that unstable flow of the "elastic turbulence" type is associated with transition of the system to the forced high-elastic state.Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 132–137, January–February, 1973.     

Master curves for elastic and plastic properties of highly concentrated emulsions

Critical comparison of dependences of elastic and plastic properties of highly concentrated emulsions (so-called “compressed” emulsions) on the concentration and droplet sizes is performed. The studied emulsions of water-in-oil type are so-called “liquid explosives.” They are characterized by different mean sizes and different droplet size distributions of the dispersed phase. Different average values (D _av, D ₃₂, and D ₄₃) are used as characteristics of droplet sizes. Experiments are carried out with emulsions of two concentrations. Aqueous phase (dispersed droplets) is presented by supercooled solutions of inorganic salt in water in a metastable state. The concentration limit of the existence of highly concentrated emulsions is determined by the condition of the closest packing of liquid droplets, which lies in the φ* = 0.77–0.80 range. In addition, there is a limiting value of the maximal size of droplets. This limiting value depends on the concentration and meets the requirement that droplets should be small enough for the solution to exist in a supercooled state. The elastic modulus and the yield stress of emulsions studied are proportional to the square of the reciprocal linear size of droplets, which contradicts some theoretical models, according to which these parameter should be proportional to the reciprocal size of droplets. Using the obtained experimental data, we constructed generalized dependences of the elastic modulus and the yield stress on the concentration and size of droplets. These characteristics are in good agreement with the experimental data.     

Quasi-optical theory of amplification of surface waves propagating above corrugated structures by a relativistic electron beam (impedance approximation)

The impedance model that describes the amplification of a monochromatic wave by a relativistic electron beam that propagates rectilinearly over a corrugated structure is constructed based on quasi-optical approach. In this model, the electric field component acting on electrons is written taking into account induced rf fields of the space charge of the beam. The dispersion equation used to determine the instability increments in various ranges of parameters has been obtained in the weak signal approximation. The efficiency of the energy exchange at the saturation stage of amplification is determined using a 2D nonlinear model in which the propagation of the wave has been described by a parabolic equation with a radiative boundary condition. The possibility of using the system under investigation to amplify submillimeter radiation has been demonstrated.     

Sol–gel transition and rheological properties of silica nanoparticle dispersions

Possible variants of the rheological behavior of silica model dispersions have been analyzed. Different types of interaction between the particles and a dispersion medium make it possible to obtain different systems from low-viscosity sols to gels. Proton-donor (water) and aprotic (dimethyl sulfoxide) media have been used for comparison. Dispersions in the aprotic medium behave as non-Newtonian viscous fluids exhibiting shear thinning or shear thickening depending on deformation rate. Aqueous dispersions are viscoelastic and viscoplastic objects that exhibit the shear thickening at stresses higher than the yield stress. The introduction of small amounts of poly(ethylene oxide) into the organic dispersion medium initiates gelation. An increase in the polymer content in the dispersion medium above the concentration corresponding to the formation of a macromolecular network promotes an increase in stiffness and strength of the gels. The rheological behavior of gels is influenced by the polymer molecular mass and its affinity for a solvent.     

Explosive spreading of a concentrated emulsion over a liquid surface

Spreading of a droplet of a concentrated oil-in-water emulsion over a water surface has been monitored. At the initial moment, this process proceeds at a high rate like an explosion. The stationary spreading is soon followed by the development of instability with the formation of a flower-shaped structure. At the final stage, the spot of the spread liquid may somewhat shrink. The characteristic times of these three stages are about 0.1, 1, and 10 s. The explosive character of the initial stage of spreading may be explained by the loss of dimensionality (3D → 2D) and the passage of the dispersion medium into the aqueous substrate with the release of a high free energy, while the subsequent spreading of the oil spot is explained by the Marangoni effect. A decrease in the energy of the interaction between dispersed phase (“oil”) particles in the emulsion leads to the phase separation. The final shrinkage of the oil spot may be due to the surface wave disturbance, which arises upon the explosive phase separation in the emulsion.