Nonequilibrium fluctuations and nonlinear response of an active bath
Nonequilibrium fluctuations and nonlinear response of an active bath
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DOI：
10.1103/physrevresearch.4.023043
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发表时间：
2021-10
影响因子：
4.2
通讯作者：
Hunter Seyforth;Mauricio Gomez;W. Rogers;J. Ross;W. Ahmed
中科院分区：
文献类型：
--
作者：
Hunter Seyforth;Mauricio Gomez;W. Rogers;J. Ross;W. Ahmed
我们分析了被动胶体探针浸入主动浴中的动力学过程，研究了三个物理过程：（1）由主动浴传递到探针的非平衡涨落，（2）探针在被驱动通过主动浴时所经历的摩擦，以及（3）探针返回到其平衡位置的力松弛。我们测量的局部力动力学，其中所有的以下特性是$\mathcal{O}（1）$：相对于活性浴颗粒的探针胶体的大小;相对于活性颗粒的特征游程长度的探针胶体的大小;和探针运动的时间尺度的持续时间的活性颗粒。我们发现，在P\'{e}clet（Pe）$\ll 1$的活性悬浮液表现出剪切稀化的溶剂粘度（但不低于），在0.85 <$ Pe $\leq 5.1$的活性浴剪切增厚，并在Pe $\geq 8.5$的活性浴的有效粘度显示出降低的增稠和平台的效果。这些结果与最近的建模和模拟的非线性流变学的各向同性的活性浴，提供实验验证，并建议模型预测延伸到中等密度的悬浮液。此外，我们观察到，力波动的分布取决于Pe，不像在被动平衡浴。最后，我们测量从活性浴到探针的能量传递速率为$\langle J \rangle \approx 10^3$ $k_B T/$s，这导致探针的有效扩散增加了$\sim 2$的系数。
We analyze the dynamics of a passive colloidal probe immersed in an active bath using an optical trap to study three physical processes: (1) the non-equilibrium fluctuations transferred to the probe by the active bath, (2) the friction experienced by the probe as it is driven through the active bath, and (3) the force relaxation of the probe returning to its equilibrium position. We measure the local force dynamics where all of the following characteristics are of $\mathcal{O}(1)$: the size of the probe colloid relative to active bath particle; the size of the probe colloid relative to the characteristic run-length of an active particle; and the timescale of probe movement to the persistence time of an active particle. We find at P\'{e}clet (Pe) $\ll 1$ the active suspension exhibits shear thinning down to the solvent viscosity (but not below); at $0.85<$ Pe $\leq 5.1$ the active bath shear thickens; and at Pe $\geq 8.5$ the effective viscosity of the active bath shows a decreased effect of thickening and plateaus. These results are in agreement with recent modeling and simulations of the nonlinear rheology of an isotropic active bath, providing experimental verification, and suggesting the model predictions extends to moderately dense suspensions. Further, we observe that the distribution of force fluctuations depends on Pe, unlike in passive equilibrium baths. Lastly, we measure the energy transfer rate from the active bath to the probe to be $\langle J \rangle \approx 10^3$ $k_B T/$s, which leads to an increase in the effective diffusion of the probe by a factor of $\sim 2$.