Experiments in which an oscillatory shear flow is superimposed on a steady-state circular shear flow between a cone and a plate were performed on non-Newtonian solutions by means of aWeissenberg Rheogoniometer. The steady-state shear stress and in a first approximation also the normal stress difference arising from the steady shear flow appear not to be influenced by the superimposed oscillatory flow. On the other hand, the dynamic moduli as obtained from the oscillatory parts of shear stress and shear flow are highly dependent on the superimposed steady rate of shear. The absolute value of the complex shear modulus decreases and the phase difference between oscillatory shear stress and shear flow increases in all cases and for all frequencies if the superimposed shear rate is increased. Consequently, this phase difference can become equal to and even larger than π/2. Between the angular frequency ω0 at which the phase difference is π/2 and the steady shear rateq the relation ω0= 1/2,q was experimentally found to exist in most cases. These dynamic results cannot be described by the current theories of viscoelasticity. The large and fast deformations imposed on the material should explicitly be taken into account.

Influence of superimposed steady shear flow on the dynamic properties of non-Newtonian fluids

A description is given of a device used for the complex measurement of visco-elestic properties of polymer systems under conditions of continuous harmonic shear deformation. The fundamental system of the device, technical properties and typical examples of determining rheological characteristics of polymer systems are dealt with.

Method for the complex study of rheological properties of polymer systems

Molecular process of stress relaxation for sheared polymer melts

1. The validity of the temperature-frequency superposition in the finite relaxation region has been confirmed for a concentrated solution of PIB filled with solid dispersed particles; 2. the apparent heat of activation of the viscoelastic relaxation times increases at and above a certain filler concentration (c=15%); 3. in the case of fillers for which the apparent heat of activation of the viscoelastic relaxation times is independent of the filler concentration, the filler only shifts the frequency functions of the components of the complex shear modulus along the logarithm of the modulus axis and the relaxation time spectrum H(θ) along the log H axis. In this case G′C/G′M=G″C/G″M=ηOC/ηOM=ηrel; 4. the effective filler concentration for c ccrit, the contour of the relaxation time spectrum changes on account of the formation of a secondary filler structure; 6. when the filler concentration c<ccrit, the dependencies of the viscosity on the shear rate for the composites and the matrix can be reduced with respect to two parameters; 7. possible methods for the reduction of flow curves by means of linear coordinate transformations have been systematized.

Rheology of filled polymers. Steady-state shear flow and periodic deformation. 1. Relaxation time spectra, viscosity

Phase state and morphological features of solutions of cellulose blends with rigid-chain thermotropic LC copolyesters and isotropic poly(m-phenyleneisophthalamide) in the highly polar donor solvent N-methylmorpholine-N-oxide are studied by DSC and polarization microscopy. The ternary phase diagram for the cellulose-copolyesters-N-methylmorpholine-N-oxide system is constructed. Rheological characteristics of the prepared solutions are studied using capillary and rotary rheometers under the regimes of continuous and periodic shear deformation. Rheological characteristics of cellulose solutions with copolyesters in N-methylmorpholine-N-oxide with their different phase states are shown to change in accordance with the traditional mechanism of flow for solutions with high specific interactions between their components. However, the character of the rheological behavior of mixtures of cellulose with poly(m-phenyleneisophthalamide) in N-methylmorpholine-N-oxide primarily stems from structural-morphological transformations in solutions taking place upon deformation.

Solutions of mixtures of cellulose and synthetic polymers in N-methylmorpholine-N-oxide

Rheological properties of polyisobutylene

The variation of mechanical characteristics of poly-p-diaminodiphenylsulphone terephthalamide solutions in DMAA with different water contents was studied during gel formation under stationary and dynamic conditions of shear. It was shown that determination of boundaries between the state of solution and gel should include the force factor, with three ranges: with low stress the material that had formed gel is deformed as an elastic material, with higher stress—effects of flow and slip coexist, at even higher stress—the decomposed gel flows with a viscosity close to the viscosity of the initial solution. A study of kinetics of gel formation of polymer solutions shows that the process is markedly accelerated with an increase of water content in the solvent. Water, apparently, makes contact easier between polymer molecules, resulting in an acceleration of the formation of nuclei in local crystallization. This is also confirmed by an attempt to describe experimental results using the Avrami equation.

Variation of mechanical properties of polysulphonamide solutions in gel formation

Thermomechanical, rheological and X-ray methods have been used to study a series of poly(decamethyleneterephthaloyl-bis-4-hydroxybenzoates) in the interval M = (0.8−4.2) × 104. The LC melts of the polymers constitute quasiviscoplastic liquids. The flow limit is probably connected with the formation of a network of dislocations. The existence of breaks in the dependences of viscosity on MM (on logarithmic scales) and on temperature (in Arrhenius coordinates) has been demonstrated. The characteristic MW and temperature ranges are linked with the presence in the region of the LC state of structures with a different level of orderliness. Depending on the specific LC structure and the intensity of deformation extrudates may be obtained not only oriented in different ways but also with a different structure of the elementary cell.

Aspects of flow and structural transitions in alkylene aromatic polyesters

In a broad temperature range, the rheological properties were studied of nematic polyacrylates differing in the structure of their mesogenic side groups: the series of poly( e -acryloyloxycaproyloxy)- p ′-methoxyphenylbenzoates in the range of M = (0.496–4.96) × 10 4 , and of poly-{1-[4(4-cyan-4′-biphenyloxy)-tetraoxycarbonyl]} ethylene of M = 1.8 × 10 5 . The rheological behaviour of the liquid-crystalline (LC) melts of these systems is characterized by a nearly linear dependence of the first difference of normal stress on shear rate in the range of Newtonian flow, and by the absence of correlation between the stationary and dynamic characteristics of the material. The activation energy of viscous flow in the isotropic and LC ranges was calculated. The value of the activation energy is affected both by the degree of order of the mesogenic side groups, and by their nature. From the character of the temperature variation of the rheological parameters, a structural transition was discovered within the LC state. This transition is interpreted as corresponding to the formation of local layer structures connected with conformational transitions in the macromolecular chain.

On the rheological behaviour of low-molecular-mass comb-like nematic polyacrylates☆

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