Institut für Theoretische Physik, Hardenbergstrasse 36, Technische Universität Berlin, D-10623 Berlin, Germany.
Phys Rev E. 2023 Jan;107(1-1):014603. doi: 10.1103/PhysRevE.107.014603.
Strongly confined colloidal dispersions under shear can exhibit a variety of dynamical phenomena, including depinning transitions and complex structural changes. Here, we investigate the behavior of such systems under pure oscillatory shearing with shear rate γover ̇=γ[over ̇]{0}cos(ωt), as it is a common scenario in rheological experiments. The colloids' depinning behavior is assessed from a particle level based on trajectories, obtained from overdamped Brownian dynamics simulations. The numerical approach is complemented by an analytic one based on an effective single-particle model in the limits of weak and strong driving. Investigating a broad spectrum of shear rate amplitudes γ[over ̇]{0} and frequencies ω, we observe complete pinning as well as temporary depinning behavior. We discover that temporary depinning occurs for shear rate amplitudes above a frequency-dependent critical amplitude γ[over ̇]{0}^{crit}(ω), for which we attain an approximate functional expression. For a range of frequencies, approaching γ[over ̇]{0}^{crit}(ω) is accompanied by a strongly increasing settling time. Above γ[over ̇]{0}^{crit}(ω), we further observe a variety of dynamical structures, whose stability exhibits an intriguing (γ[over ̇]{0},ω) dependence. This might enable new perspectives for potential control schemes.
在剪切下强烈受限的胶体分散体可以表现出多种动力学现象，包括去钉扎转变和复杂的结构变化。在这里，我们研究了在纯振荡剪切下（剪切速率为γover ̇=γ[over ̇]{0}cos(ωt)）此类系统的行为，因为这是流变实验中的常见情况。胶体的去钉扎行为是根据轨迹从颗粒水平进行评估的，这些轨迹是通过过阻尼布朗动力学模拟获得的。数值方法通过基于弱和强驱动极限的有效单粒子模型的分析方法进行补充。研究了广泛的剪切速率幅值γ[over ̇]{0}和频率ω，我们观察到了完全钉扎和临时去钉扎行为。我们发现，临时去钉扎发生在剪切速率幅值超过频率相关的临界幅值γ[over ̇]{0}^{crit}(ω)时，我们得到了一个近似的函数表达式。对于一系列频率，接近γ[over ̇]{0}^{crit}(ω)伴随着settling time 的强烈增加。在γ[over ̇]{0}^{crit}(ω)以上，我们还观察到了多种动力学结构，其稳定性表现出有趣的（γ[over ̇]{0}，ω）依赖性。这可能为潜在的控制方案提供新的视角。
