The article presents the results of experiments on studying of rheological behaviour of dilute solutions of agar-agar. The chosen range of concentration 0,1–0,7% allows to avoid gelation at ambient temperature. Dependence of viscosity and shear stress on concentration, shearing speed and temperature in an interval 25–45 °С is investigated. It was found that the concentration dependence of viscosity severely depends on the shear speed, a nonlinearity is observed that increases with decreasing shear speed. The dependence of the viscosity on the shear speed for concentrations of 0,3–0,7% has a similar but gradually changing type of the asymptotic decrease, whereas for 0,1%, solution dependence linearly grows with increase of shear speed. The interrelation of viscosity and shear stress is studied. Curves for solutions of 0,3–0,7% have a similar type and differ significantly from curves for 0,1% solutions. Moreover, the dependencies are not typical for polymer solutions. The activation energy of viscosity and shear stress is studied. For two temperature intervals: 25–35 and 35–45 °C, there is no correlation and a smooth dependence of the measured parameters on temperature. The activation energy of both viscosity and shear stress not decreases with temperature increase, as one might expect, but increases, for many times. This fact is observed completely individually for the different concentrations. An explanation is proposed for the observed dependences, which is based on the assumption of a structural change in agar-agar solutions, which is caused by changing the concentration of solution and magnitude of the mechanical influence.
The effectiveness of high frequency electromagnetic field influence on the analytical signal value in the stripping voltammetry method depending on such factors as the nature and concentration of the defined element, nature and concentration of the supporting electrolyte and agitation velocity has been studied. It has been demonstrated that an analytical signal increase may be achieved that allows one to lower a detection limit and to reduce the time of individual definition. The highest peak current is observed at some definite frequencies of the exterior field depending on the nature of the element and on the supporting electrolyte as well.
The paper presents the results of a study of the rheological properties of agar-agar solutions prepared using water exposed to an electromagnetic field with a frequency of 30 to 170 MHz. The studies were carried out at three temperatures: 25, 35, 45 °С, the concentration varied from 0.1 to 0.7%, and the shear rate varied in the range of 100–1000 s-1. As a result of the study, a distinct influence of the electromagnetic field was found, and the quantitative response depends on the shear rate, solution concentration, temperature and frequency of the electromagnetic field. In the vast majority of cases, a decrease in the viscosity of solutions is observed as a result of exposure to an electromagnetic field. There is practically no quantitative correlation of viscosity changes with frequency. There is a complex picture of the mutual influence of the solution concentration, the frequency of the electromagnetic field, temperature and shear rate when measuring viscosity. The temperature dependence of viscosity for solutions subjected to and not exposed to an electromagnetic field is multidirectional in nature and substantially depends on both the concentration of the solution, the frequency of the electromagnetic field, and the shear rate at which measurements were taken. An explanation of the observed dependencies is proposed, which is based on the two-component agar-agar solutions, which leads to individualization of the changes in the rheological properties determined by agarose and agaropectin, respectively.
The influence of a high-frequency electromagnetic field on the process of water crystallization has been stud-ied.Water irradiated by аfield at 30–200 MHz was kept from 0 to 21 days, then it was frozen. Volumes of ice at crystallization were compared for water irradiated and unirradiated by the field. Values located more or less symmetrically near zero; 2) values with a predominantly positive shift, and 3) values for which the shift is mostly negative. Positive shift was noted when combining 200 MHz and the exposure time up to 11 days. The maximum effect of relative volume increase almost two times was observed at 200 MHz and one day ex-posure time. The maximum compression of ice approximately three times compared to the unirradiated sam-ple occurred twice: after field effect at 90 MHz and exposure time of 11 days, and at 140 MHz and exposure time of 21 days. The similarity of time dependence at 170MHz with the dependence of thermal effect of glu-cose dissolution found in early works was noted.The data obtained confirm that field effect results in both strengthening and loosening of water structure
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