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Analysis of literature data and our own experimental observations have led to the conclusion that, at high deformation rates, viscoelastic liquids come to behave as rubbery materials, with strong domination by elastic deformations over flow. This can be regarded as a deformation-induced fluid-to-rubbery transition. This transition is accompanied by elastic instability, which can lead to the formation of regular structures. So, a general explanation for these effects requires the treatment of viscoelastic liquids beyond critical deformation rates as rubbery media. Behaviouristic modeling of their behaviour is based on a new concept, which considers the medium as consisting of discrete elastic elements. Such a type of modeling introduces a set of discrete rotators settled on a lattice with two modes of elastic interaction. The first of these is their transformation from spherical to ellipsoidal shapes and orientation in an external field. The second is elastic collisions between rotators. Computer calculations have demonstrated that this discrete model correctly describes the observed structural effects, eventually resulting in a “chaos-to-order” transformation. These predictions correspond to real-world experimental data obtained under different modes of deformation. We presume that the developed concept can play a central role in understanding strong nonlinear effects in the rheology of viscoelastic liquids.

Rheological properties of concentrated oil-in-water emulsions containing dissolving polymers in both phases, partially playing a role of surfactants, were studied. Additionally, nanoparticles were added to the aqueous phase, and they had an influence on rheological behavior and emulsion stability. The main peculiarity of the objects is the superposition of viscoelastic properties related to the presence of polymers and to interface interactions. Emulsion viscoelasticity were characterized by three separate relaxation modes with very different relaxation times. They reflect relaxation processes of polymeric origin inside both phases, which are dilute polymer solutions, and elasticity of interface layers. Presence of nanoparticles strongly affects the rheological properties leading to the increase in the apparent viscosity, elastic modulus, and yield stress of emulsions.

The combined superimposing influences of the surface area of silica nano-particles and molecular weight of polyethylene oxide matrix on the rheological properties of suspensions have been studied. The parameters of both components varied over a wide range: the surface area of silica from 100 to 390 m 2 /g, molecular weight of poly(ethylene oxide) from 200 to 2 × 10 5  Da, and concentration of silica from 1 to 13 vol%. In all cases, silica formed aggregates in suspension with apparent diameters of 50 to 230 nm; the higher values were observed for particles with larger surface area. Low-concentration suspensions in an oligomer matrix showed a slight non-Newtonian behavior; the size of silica particles was a determining parameter. Increasing the silica concentration led to dilatancy at high shear stresses. There was a threshold in the concentration dependence of viscosity, beyond which gelation of suspensions occurred. Depending on the silica concentration and molecular weight of the polymeric matrix, the dispersions behaved more like typical colloidal suspensions in a low molecular weight matrix or viscoelastic polymer melts containing an amount of solid filler. An increase in molecular weight of the polymeric matrix resulted in competition between increase in viscosity, appearance of viscoelasticity, and finally the transition from the gel state of a suspension in viscous medium to an elastic fluid.

A new method for determining parameters of a relaxation spectrum of visco-elastic bodies is proposed. The basic idea of the method consists of presenting measured frequency dependencies of the dynamic modules components by the power series. The coefficients of these series are found by comparing varying values with experimental data by linear functional of errors. The parameters of a spectrum are then calculated from the coefficients of the series. This procedure allows us to overcome the main problem of finding relaxation times, i.e. to pass from non-linear to linear functional of errors. It gives us the unique possibility of unambiguously estimating weights (partial moduli) of lines in a discrete relaxation spectrum and relaxation times because there is only a single minimum in the functional of errors.

A flow channel for experimental modeling of the structural reaction injection molding (SRIM) process, for producing composites with a sandwich‐like structure, has been designed and constructed. It consists of a thin rectangular box, in which the reinforcing glass fabrics with different permeabilities are positioned parallel to each other. The core layer is a thick, porous mat. Location of the other denser and thinner reinforcing materials into the flow channel was symmetrical with respect to the spacer mat. The channel has transparent walls for observing propagation of the impregnation front in the spacer mat and in the reinforcing dense layers. Development of the impregnation front during filling the flow channel and the pressure profile in the gate were measured for non‐foaming reactive polyurethanes. Enough good correspondence between the calculated and experimentally observed flow front position and pressure profiles was obtained.

A mathematical model of the infusion process in producing reinforced articles is proposed. The model is based on the analysis of flow of a Newtonian liquid inside a rectangular multilayer channel. According to the model, a liquid enters the central (feeding) layer, moves through this layer, and simultaneously impregnates peripheral layers. So, the flow is two‐dimensional. Flow inside the porous layers is treated in terms of the Darcy equation with different permeability coefficients in two directions. Principal solutions for the flow front development and pressure evolution were obtained and analyzed. Then the initial model, developed for a Newtonian liquid, is generalized for the so‐called “rheokinetic” liquid, which changes its rheological properties in time as a result of temperature variation and/or any possible chemical process, in particular, the reaction of curing of a binder. It was proven that in this case the solution is automodel. This means that the solutions obtained for a Newtonian liquid in the dimensionless form are valid for an arbitrary rheokinetic liquid.

Rheological properties of highly concentrated emulsions of the water-in-oil type were studied. Water phase (concentration approximately 91%) consists of a supersaturated aqueous solution of nitrate salts; water comprises less than 20% by mass. The average size of droplets, D, in the emulsions was varied. It was found that the emulsions are non-Newtonian liquids and flow curves measured in a sweep regime of shearing have clear low-shear-rate Newtonian domain. The complete flow curves are fitted by the Cross equation. The elastic modulus is practically constant in a very wide frequency range. Hence the viscoelastic relaxation processes might be expected at times >>100 s and in the short-term side of the curve at approximately 0.01 s. The elastic modulus (measured in oscillating testing and in elastic recovery as well) is proportional to D-2 while the Newtonian viscosity is proportional to D−1.The time effects were observed: it was found that the emulsions behave as rheopectic materials because prolonged shearing results in an increase of viscosity in the low shear rate domain of several orders of magnitude.

The kinetics of curing of several phenolic resin compounds were studied with the use of four techniques: viscometry, infrared spectroscopy (IR), differential scanning calorimetry (DSC), and thermomechanical analysis. The objective was to compare the effectiveness of these methods. It was found that the viscosity increase during oligomer curing can be described by an exponential function, and that the rate of viscosity increase can be described in terms of a “viscometric” kinetic constant, kη. The gel‐time, t*, was found by extrapolation of the time dependence of the reciprocal viscosity. The product (t*kη) appears to be constant for all temperatures. It was concluded that each experimental technique reflects a different kinetic process, and it is not possible to correlate the results of one technique with those of another. The degree of conversion at the gel point, β*, depends on temperature, and it is thought that this is due to the heterogeneous nature of curing. The glass temperature (as determined from the maximum in the loss tangent) is related to the degree of curing by the DiBenedetto equation, which can be used to determine the degree of conversion during the final stages of the reaction. POLYM. ENG. SCI. 45:95–102, 2005. © 2004 Society of Plastics Engineers

The analysis of the Fourier Transform Mechanical Spectroscopy (FTMS) method in application to measuring viscoelastic properties of a material in a linear viscoelastic domain shows that sensitivity of the method at higher harmonics strongly depends on the form of the input signal. Then the problem of the choice of the optimal signal is discussed. It is shown that the function f(t)=(sinωt)/t provides the best form of the input signal basing on the requirement to hold equal amplitudes of all higher harmonics. The comparison of data obtained by the FTMS method and viscoelastic properties measured in harmonic oscillations demonstrates that both methods give adequate results.The application of the FTMS method with the input signal of the optimal form for measuring linear viscoelastic properties of a material saves time of an experiment (up to 3–4 times) and might be specially interesting for analysis of unstable (“rheokinetic”) materials, in particular, curing oligomers, because the time evolution of different relaxation modes can proceed in different manner.

The main goal of the paper is to compare predictive power of relaxation spectra found by different methods of calculations. The experimental data were obtained for a new family of propylene random copolymers with 1-pentene as a comonomer. The results of measurements include flow curves, viscoelastic properties, creep curves and rubbery elasticity of copolymer melts.Different relaxation spectra were calculated using independent methods based on different ideas. It lead to various distributions of relaxation times and their “weights”. However, all of them correctly describe the frequency dependencies of dynamic modulus. Besides, calculated spectra were used for finding integral characteristics of viscoelastic behaviour of a material (Newtonian viscosity, the normal stress coefficient, steady-state compliance). In this sense all approaches are equivalent, though it appears impossible to estimate instantaneous modulus.The most crucial arguments in estimating the results of different approaches is calculating the other viscoelastic function and predicting behaviour of a material in various deformation modes. It is the relaxation and creep functions. The results of relaxation curve calculations show that all methods used give rather similar results in the central part of the curves, but the relaxation curves begin to diverge when approaching the high-time (low-frequency) boundary of the relaxation curves. The distributions of retardation times calculated through different approaches also appear very different. Meanwhile, predictions of the creep curves based on these different retardation spectra are rather close to each other and coincide with the experimental points in the wide time range. Relatively slight divergences are observed close to the upper boundary of the experimental window.All these results support the conclusion about a rather free choice of the relaxation time spectrum in fitting experimental data and predicting viscoelastic behaviour of a material in different deformation modes.