论文标题
在振荡性剪切下的闭合胶体分散剂的动力学
Depinning dynamics of confined colloidal dispersions under oscillatory shear
论文作者
论文摘要
剪切下的强限胶体分散体可以表现出各种动力学现象，包括渗透过渡和复杂的结构变化。在这里，我们研究了这种系统在纯振荡剪切下的行为，剪切速率$ \dotγ（t）= \dotγ_0\ cos（ωt）$，因为它是流变学实验中的常见情况。胶体的繁殖行为是根据基于轨迹的颗粒水平评估的，该轨迹从过度阻尼的布朗动力学模拟获得。基于有效的单粒子模型的分析方法，在弱和强驱动的范围内，数值方法得到了补充。调查了一系列剪切速率振幅$ \dotγ_0$和频率$ω$，我们观察到完整的固定以及临时销售行为。我们发现，对于频率依赖性的临界幅度$ \dotγ_0^\ mathrm {crit}（ω）$以上的剪切速率振幅发生的临时静止。对于一系列频率，接近$ \dotγ_0^\ mathrm {crit}（ω）$伴随着强烈的沉降时间。高于$ \dotγ_0^\ mathrm {crit}（ω）$，我们进一步观察到各种动态结构，其稳定性表现出有趣的（$ \dotγ_0，ω$）的依赖性。这可能使潜在控制方案的新观点。
Strongly confined colloidal dispersions under shear can exhibit a variety of dynamical phenomena, including depinning transitions and complex structural changes. Here, we investigate the behaviour of such systems under pure oscillatory shearing with shear rate $\dotγ(t) = \dotγ_0 \cos(ωt)$, as it is a common scenario in rheological experiments. The colloids' depinning behaviour 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 $\dotγ_0$ and frequencies $ω$, we observe complete pinning as well as temporary depinning behaviour. We discover that temporary depinning occurs for shear rate amplitudes above a frequency-dependent critical amplitude $\dotγ_0^\mathrm{crit}(ω)$, for which we attain an approximate functional expression. For a range of frequencies, approaching $\dotγ_0^\mathrm{crit}(ω)$ is accompanied by a strongly increasing settling time. Above $\dotγ_0^\mathrm{crit}(ω)$, we further observe a variety of dynamical structures, whose stability exhibits an intriguing ($\dotγ_0, ω$) dependence. This might enable new perspectives for potential control schemes.
