Rheological characteristics analysis of shear thickening fluids based on response surface methodology
This paper analyzed the influence of various components and the external environment on the rheological properties of shear thickening fluid (STF). The single-factor experimental study was carried out with the silica particle size, the mass fraction of silica particles, the continuous phase's average molecular weight, and the temperature as the influencing factors. Obtain the influence of various factors on the initial viscosity, critical shear rate, thickening period and thickening ratio of STF samples. According to the crossover relationship between the shear stress and the intermolecular force when the shear thickening occurs, the STF's critical shear rate criterion is constructed. By introducing the mechanical balance between small molecules, the relationship between the particles' volume fraction and the distance between particles in the suspension system is established. The influencing factors and formulas of the STF's critical shear rate and shear capacity are deduced, which supports the conclusions obtained in the single-factor experiment. Based on the single-factor experiment conclusion, the mass fraction of silica particles, the average molecular weight of the continuous phase and the temperature are used as the influencing factors, and the critical shear rate, shear thickening ratio and maximum viscosity are the responses indicators. According to the Box-Behnken response surface methodology (RSM) design, 15 analysis experiments with three factors and three levels are carried out. Obtain the rheological characteristics of the STF and regression equation between each factor, based on the three-dimensional response surface graph and F-value in ANOVA result. We found that among the interaction effects, the interaction between the continuous phase's average molecular weight and the temperature has the most significant impact on the critical shear rate of the STF. The interaction between the silica particles' mass fraction and the continuous phase's average molecular weight significantly impacts the shear thickening ratio of the STF. The interaction between silica particles' mass fraction and the temperature has the most significant impact on the maximum viscosity of the STF. Finally, according to the response surface methodology experimental results and ideal STF rheological characteristics standard in engineering applications, when the mass fraction of silica particles is 35%, the average molecular weight of the continuous phase is 387, and the temperature is 20 °C. The critical shear rate of the STF system is 5.84 1/s, the shear thickening ratio is 102.8, and the peak viscosity is 1191.7 Pa·s, reaching the optimal theoretical value within the value scope.
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