International Conference on Rheology and Fluid Mechanics November 10-11, 2016 Alicante, Spain

Clara A. Tovar is Doctor on Physical by the University of Vigo (Spain) in 1996. She is the director of the laboratory of biopolymers rheology in the Faculty of Science of Ourense (Spain). She has published 50 papers in reputed journals.

Two lots of aqueous native (N) glucomannan dispersions at a concentration of 5 g/100mL were made at pH=5.3, N (no pressurized lot) and N200 (lot subjected to high hydrostatic pressure of 200MPa). Both lots were stored at -20 °C during two years (FN (frozen no pressurized) and FN200 (frozen-pressurized)), to examine the role of 200MPa on the viscoelastic parameters at the linear viscoelastic (LVE) range after frozen storage. All samples exhibited gel-like behaviour at 25 °C. From stress sweeps, the structural damage associated to frozen storage was observed in the decrease of stress (max) (66.5%) and strain (max) (66%) amplitudes of FN comparing with N, but complex modulus (G*) remained constant (4.20.2 kPa). Nevertheless, 200MPa improved weakly these results, because max decreased something less (62%) and similarly for max (59%). Loss factor (tan) was reduced similarly (23%) in FN200 and FN indicating that frozen storage enhanced the solid-like nature in both lots but maintaining the initial rigidity. Thus, frozen storage produced larger (rod-like) junctions, in line with the lower max and max, and more energy stable interactions by hydrogen bonding in both FN200 and FN relative to N200 and N respectively. This rheological response was corroborated by mechanical spectra, because the ideal-fraction network (Fin) was higher and more time-stable at lower frequencies in both frozen lots, more noticiable in FN200. The specific structural benefits of 200MPa were also shown in thermal profiles, particularly in the low and constant values of tan at 25-90 °C range.

Bair Damdinov - PhD, Dr. of Sci., Dean of faculty of physics at the Buryat State University (BSU, Ulan-Ude); higher scientific researcher at molecular physics lab, Institute of physical material science of Russian Academy of Sciences (Siberian Division). Scientist, Lector, Administrator. Specialist in condense matter physics. Research fields: Physical Acoustics, Physics of condense matter, Physical chemistry. The research of viscoelastic properties of liquids by acoustic method. Viscoelastic relaxation in liquids at low frequencies.

In this article, the shear properties of different liquids are measured. There is a wide class of fluids and multiphase media that are able to change their viscosity under the action of an external load, displaying visco-elastic relaxation properties. Rheological measurements are a powerful indirect method for studying the physicochemical properties of these materials and their states. Dynamic tests allow the elastic and viscous components of mechanical response to be distinguished and the results to be presented in the form of complex moduli of elasticity. The paper discusses rheological method for the determination of the shear modulus and loss modulus of the liquids (Fig.1). Real and imaginary shear modulus and effective viscosity of the liquids and nanoparticle suspensions are measured by the method at various frequencies and temperatures. It was shown that the nanoparticles play a crucial role in the visco-elastic properties of modified suspensions. It was shown that these properties depend on sizes and distributions of nanoparticles. We hypothesize that dynamic structural microinhomogeneity is a feature of both polymers and fluids, and not only highly viscous but also ordinary, less viscous fluids. There is no fundamental difference between highly viscous and ordinary fluids. There is only a quantitative difference. A low-frequency visco-elastic relaxation process is assumed to occur in a fluid with a period of relaxation much longer than the lifetime of the individual fluid particles.