Zhu W, Xia Y, Aitken B G, Sen S
Department of Materials Science and Engineering, University of California at Davis, Davis, California 95616, USA.
Science and Technology Division, Corning Incorporated, Corning, New York 14831, USA.
J Chem Phys. 2021 Mar 7;154(9):094507. doi: 10.1063/5.0039798.
The onset of shear thinning and the transition from Newtonian to non-Newtonian behavior in the viscous flow of select chalcogenide and oxide network glass-forming liquids in the deeply supercooled regime and its temperature dependence are studied using parallel plate rheometry. In all cases, the onset occurs at a shear rate γ̇ that is several orders of magnitude lower than the shear relaxation rate τ and the former increases with increasing temperature. These results are in good qualitative agreement with the predictions of the existing models of shear relaxation and shear thinning based on the nonlinear Langevin equation theory, random first order transition theory, and the free volume model. However, in contrast to the theoretical predictions, the reduced shear rate W (=τγ̇) at the onset is found to range between 10 and 10 and decrease with increasing temperature. This temperature dependence becomes stronger with increasing fragility of the liquid. These results likely indicate that the shear thinning mechanism in network liquids could be fundamentally different from those in molecular, metallic, or polymeric glass-formers.
利用平行板流变仪研究了在深度过冷状态下，特定硫族化物和氧化物网络玻璃形成液体粘性流动中剪切变稀的起始以及从牛顿行为到非牛顿行为的转变及其温度依赖性。在所有情况下，起始发生在剪切速率γ̇，该剪切速率比剪切弛豫速率τ低几个数量级，并且前者随温度升高而增加。这些结果与基于非线性朗之万方程理论、随机一阶转变理论和自由体积模型的现有剪切弛豫和剪切变稀模型的预测在定性上高度一致。然而，与理论预测相反，发现起始时的约化剪切速率W（=τγ̇）在10到10之间，并随温度升高而降低。随着液体脆性增加，这种温度依赖性变得更强。这些结果可能表明，网络液体中的剪切变稀机制可能与分子、金属或聚合物玻璃形成体中的机制有根本不同。
