Possibilities of using rheological parameters as physical indicators of soil structural changes

The rheological parameters of structured soddy-podzolic soils (Albic Glossic Retisols (Lomic, Cutanic)) and chernozems (Haplic Chernozems (Loamic, Pachic)) in their natural state and involved in agricultural use were studied by the oscillation amplitude sweep test. Shear resistance parameters of the studied soils (shear stress at the end of the linear viscoelasticity range – LVE-range tL, shear stress tF at the Crossover point and maximum shear stress tmax) were more informative and indicated pronounced differences between soil genetic horizons in contrast to viscoelasticity parameters (deformation γL at the end of the LVE-range and the integral zone Z) when comparing natural and arable soils. The agricultural land use resulted in decreased organic carbon content and, as a consequence, reduced viscoelasticity and shear resistance of the soils. At the same time, the higher bulk density of arable horizons and the redistribution of fine soil particles (physical clay) could explain maximal values of the rheological parameters in the upper arable horizons and their slight differentiation with depth. Further development in the application of the proposed and studied rheological parameters can give insight into the nature and strength evaluation of interparticle bonds, the soil processes under the impact of agricultural machinery, and can also be integrated into the system of physical indicators of soil structural changes

Rheological properties of natural and disturbed structure samples of soddy-podzolic and agro soddy-podzolic soil

The rheological properties of two profile`s horizons of soddy-podzolic and agro soddy-podzolic soil were studied by the amplitude sweep test on a rheometer MCR-302 (Anton Paar, Austria) on samples of natural structure (pastes) and disturbed structure (monoliths). Curves of the elasticity and viscosity modules determine the linear viscoelasticity range (LVE-range) of soil pastes and monoliths, the elastic modulus in linear viscoelasticity range as a characteristic of strength of structural bonds, the transition from viscoelastic to viscous behavior-the intersection of the elasticity and viscosity modules. It is established that the LVE-range of monolithic samples is more than paste samples, they are characterized by stronger structural bonds in the linear viscoelastic range; however, the destruction of structure in monolithic samples occurs at lower deformation values than in paste samples. The differentiation of the rheological parameter values of the upper part of profile of soddy-podzolic soil is caused by the large content of organic matter in the humus horizon and the facilitation of the soil texture in the eluvial horizon. The strength of structural bonds of the samples of the lower horizons of soddy-podzolic and agro soddy-podzolic soils differ insignificantly

A Dramatic Change in Rheological Behavior of a Clay Material Caused by a Minor Addition of Hydrophilic and Amphiphilic Polyelectrolytes

Wide usage of clay-based materials in industry requires investigations concerning efficient modification techniques to control their mechanical behavior in aqueous media. The challenging problem in this field involves minimization of the modifying agent content to provide marked changes in the operating characteristics of the material. In this work, the physicochemical, mechanical and structural aspects of the interaction of capillary water-saturated kaolinite with polyelectrolytes were studied. Modification of kaolinite with a negligible amount (0.1 wt.%) of hydrophilic and amphiphilic polyelectrolytes provides the control for rheological parameters of kaolinite suspensions such as storage and loss modulus in the range of three orders of magnitude. The results obtained reveal the wide possibilities for the production of a spectrum of clay materials using minor amounts of polymer modifying agents

Competitive Biosynthesis of Bacterial Alginate Using <em>Azotobacter vinelandii</em> 12 for Tissue Engineering Applications

This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (Mw) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal Mw (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low Mw). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering