Yu. G. Yanovsky

Resonance behavior of viscoelastic fluids in Poiseuille flow and application to flow enhancement

Resonance-like phenomena in axisymmetric Poiseuille flows of viscoelastic fluids are studied. It is shown that instantaneous flow velocities of the upper convected Maxwell fluid with a spectrum of relaxation times drastically increase at certain frequencies of the oscillating pressure gradient. This effect becomes more pronounced as the tube radius gets smaller. Non-linear constitutive structures are also considered to show that the most effective mean flow rate enhancement for pulsating flows can be reached at the resonance frequencies.

Influence of Vibrations on the Viscoelastic Behavior of Monodisperse Polybutadienes

Abstract The viscoelastic behavior of monodisperse polybutadienes is studied at different amplitudes of cyclic deformation. The concept of initial relaxation spectrum is introduced, this spectrum corresponding to small amplitudes. Under the action of high amplitudes the relaxation spectrum changed. This changed-effective spectrum can be calculated by means of the linear theory of viscoelasticity. The initial spectra of monodisperse polybutadienes have maxima. Under the action of high amplitudes the long-time parts of the spectra are truncated and the maxima shift into the short-time regions. There is an unambiguous correspondence between the amplitude of the deformation rate on cyclic deformation and the rate of shear on continuous deformation. It is shown that the length of the high-elasticity plateau, estimated on a logarithmic scale of relaxation times, and the maximum relaxation times of polybutadienes, as well as their initial Newtonian viscosities are dependent on molecular weight to a power of 3.6....

Linear inverse problems in viscoelastic continua and a minimax method for Fredholm equations of the first kind

A new theory based on an extensively modified version of the minimax method is proposed to estimate the cause from the result, that is, the characteristic functions of viscoelastic media from experimentally obtained material functions through the solution of Fredholm integral equations of the first kind. The method takes into account the non-Gaussian outliers, and does not require the assumption of a priori error bounds as in other smoothing techniques which may lead to instability or to a stable solution not representative of the true solution. The algorithm is applied to several hypothetical test problems to show the excellent performance of the method in extreme severe conditions. The shortcomings of the Tikhonovs regularization and other smoothing techniques are discussed. It is shown that the solution via these methods may not represent the real solution in any norm. The new method is applied to linear viscoelasticity to obtain the relaxation spectrum from experimental material functions. The relaxation spectra of some materials obtained via the proposed adaptive-robust minimax algorithm and experiments run in a rotary viscometer are presented.

Viscoelastic Characteristics of Polymers of Narrow Molecular-Mass Distribution in Various Physical States According to Data on Small-Amplitude Oscillating Shear

Abstract This work is concerned with the results of dynamic investigations of 1,2-polybutadienes of narrow molecular-mass distribution over a wide temperature-frequency range covering various physical states of the material, from the fluid to the glassy state. The limits of applicability of the use of the temperature-frequency reduction are given. The experimental results have been obtained under the following test conditions: at variable frequency and constant temperature; at variable temperature and constant frequency.

Viscoelasticity of Solutions and Blends of Narrow Molecular-mass Distribution Polymers

Abstract A study has been made into the initial values of viscoelasticity parameters that characterized the binary polymer systems containing 1,4-polybutadienes, produced by anionic polymerization and having a relatively narrow molecular-mass distribution (M w/M n ≤ 1.1–1.2). These binary systems contained polymers with M/M c > 1. On the one hand, the latter ratio approached 2, on the other, they contained high-molecular components with M/M c exceeding 300. The binary systems contained the high-molecular components in the amount of 0.1 to 20% which permitted determining the intrinsic characteristic values of viscosity [η] and elastic coefficient [A O G]. It has been found that from the above-mentioned sample of PB two types of the systems can be formed: 1) solutions of a high-molecular-mass polymer in a low-molecular one; 2) blends of polymer with well developed entanglement network. In the first case the intrinsic values of the viscosity and the coefficient of elasticity are presented in the following fo...

Quantum mechanics simulation and experimental study of adhesive interaction and aggregation of carbon-silicate nanoparticles—reinforcing fillers of polymer composites

Nanoparticles are widely used as polymer composite-reinforcing additives—fillers. Understanding the interaction mechanisms and regularities responsible for nanoparticle aggregation is of great significance for elucidating the nature of reinforcing of polymer composites. The paper reports on quantum mechanics calculations and full-scale experimental study of adhesive interaction of carbon and silicate adsorption complexes (nanomodels of active filler particles of polymer composites). The quantum mechanics approach allowed describing the adhesive properties of particle aggregates reasoning from nanoscopic structure of their surface. The quantum mechanics data were checked for adequacy on schungite—a natural mineral containing carbon and silicate. Schungite microparticles were milled to nanosizes by colloidal grinding in various disperse liquid media (alcohol, acetone, water) and the structure and properties of aggregated schungite micro- and nanoparticles were studied; fractal analysis of their surface was performed. It is found that smaller aggregates of silicate and carbon particles with higher surface fractal dimension are formed in colloidal grinding with small molecular sizes of disperse media (in our case, ethanol or methanol) and this agrees with the data predicted by quantum mechanics calculations.

Investigation of magnetite-nanoparticle agglomeration on the surface of structured polyamide films

An atomic force microscopy investigation into the deposition of nanoscale magnetite from drops of an aqueous suspension applied to the surface of a porous polymer film is conducted. Analysis of the micros-copy images reveals the formation of agglomerates and a certain orientation of the deposited magnetite nanoparticles due to anisotropy of the structured space of the porous material and magnetic interaction of the nanoparticles with each other.

Comparative Investigations of Structure and Absorptive Capacity of Nano- and Microsized Magnetic-Operated Particles for their Application in Medicine and Biology

For the first time, the comparative investigations of structure and sorption efficiency of nano- and microsized magnetic-operated particles in respect to both the antigen and virus hepatitis B and also to the substance-markers (low-, middle- and highmolecular substances) were carried out. The sorption efficiency of magnetic particles: magnetite (Fe3O4), cobalt-ferrite (CoFe2O4), composite ferro-carbon (FeC) to the substances of different molecular weight was evaluated in vitro experiments. The high absorptive capacity to low- and highmolecular substance-markers has been observed for microsized composites of FeC. Absorptive capacity of the nanosized Fe3O4 and CoFe2O4 particles to the substance-markers was low. But the nanosized Fe3O4 and CoFe2O4 particles had a good absorptive capacity to virus of hepatitis B and its antigen (HBsAg). The sorption efficiency results of nano- and microsized magnetic particles correlate with the structure of their surface.

Studies on surface structure of polymer membranes - biosensor carriers with dynamic force microscopy

Useful information about the surface pore structure of polymeric track and Millipore membranes chosen as biosensor carriers have been obtained using the easyScan dynamic force microscope

Nano-Modeling Structure and Micromechanical Properties of Mesoscopic Composite Systems

We discuss the results of molecular modeling (quantum mechanics and molecular dynamics methods) of mesoscopic composite systems based on thermoplastic (polyethylene, polypropylene, etc.) and elastomeric (polybutadiene, polyisoprene, etc.) polymer matrices and active nanofillers (commercial carbon in different structural modifications, silicate, fullerens, nanotubes). Consideration is given to the structure, energy and micromechanical properties of model particles of commercial carbon, including those with surfaces terminated with various chemical compounds, and to the adsorption of various polymer chains on them. Shear strain and uniaxial tension in different adsorption complexes as well as molecular friction are calculated. The reinforcement effect, i.e. the change of most important physico-mechanical characteristics, and energy parameters are analyzed. We make important inferences about the influence of filler properties on its activity during interaction with polymer matrix particles. It is noticed that the best adhesion of polymer chain fragments (largest force of microscopic molecular friction) is observed for the isoprene elastomer — silicate filler system. Such nanoparticles as fulleiene and carbon nanotubes exhibit weak (almost equal) molecular adhesion, which makes it impossible to consider them as promising reinforcing fillers without proper modification. Carbon fillers are found to exert a different effect on the structure of thermoplastics and elastomers. In the first case, the structure becomes amorphous, while in the second one it stabilizes. This explains the known effect of elastomer reinforcement with carbon fillers. Thus, we have developed molecular simulation algorithms and methods, which employ parallel computing technologies on a supercomputer, to study the structure and micromechanical characteristics of large molecular systems, namely, clusters of representative elements of polymer composites. Based on the investigation by quantum mechanics and molecular dynamics methods, conclusions have been made concerning the effect of the filler nature on its interaction with polymer molecules comprising the polymer composite matrix.