标题： 胶体在活性液体中的非常规相分离和分形界面 显示英文标题

标题： Unconventional Phase Separation and Fractal Interfaces of Colloids in Active Liquids

摘要： 由非平衡涨落驱动的相分离是活体和合成活性物质的显著特征。 与平衡系统不同，平衡系统中的有序态源于自由能的最小化，而活性系统则在微观尺度上持续注入能量。 这种驱动系统中有序相的出现挑战了我们对畴生长和界面结构的传统观点。 在本研究中，我们研究了含有大肠杆菌的活性液体中胶体簇的粗化过程。 我们的实验表明，胶体和游动粒子的均匀分散体本质上是不稳定的，导致自发的相分离，其特征是分形界面和非常规的动力学。 序参量的相关函数表现出动态标度，胶体畴的大小随 $t^{1/z}$增长，其中 $z \sim 4$，与具有守恒序参量的热系统的著名生长定律相反。 此外，结构因子表现出非Porod行为，表明具有分形界面的畴。 这种非Porod行为也体现在相关函数中的尖峰奇异性上。 我们使用一种标量场理论来解释实验结果，其中游动粒子活动引起的非平衡涨落被建模为时空相关的噪声。 这个打破时间反演对称性和细致平衡的粗粒化模型成功再现了关键的实验观察结果。 此外，它揭示了一种波动的微相分离，其中初始的畴生长遵循 $t^{1/4}$标度，最终被阻止，从而为活性液体中胶体非常规相分离的微观起源提供了新的见解。 显示英文摘要

摘要： Phase separation driven by nonequilibrium fluctuations is a hallmark of both living and synthetic active matter. Unlike equilibrium systems, where ordered states arise from the minimization of free energy, active systems are fueled by a constant injection of energy at the microscopic scale. The emergence of ordered phases in such driven systems challenges our conventional views of domain growth and interfacial structure. In this study, we investigate the coarsening of colloidal clusters in active liquids containing E. coli. Our experiments reveal that uniform dispersions of colloids and swimmers are inherently unstable, resulting in spontaneous phase separation characterized by fractal interfaces and unconventional kinetics. The correlation function of the order parameter displays dynamical scaling, with the size of colloidal domains growing as $t^{1/z}$, where $z \sim 4$, in contrast to the well-known growth laws for thermal systems with a conserved order parameter. Furthermore, the structure factor exhibits non-Porod behavior, indicating domains with fractal interfaces. This non-Porod behavior also manifests itself as a cusp singularity in the correlation function. We elucidate our experimental findings using a scalar field theory in which the nonequilibrium fluctuations arising from swimmer activity are modeled as spatio-temporally correlated noise. This coarse-grained model, which breaks time-reversal symmetry and detailed balance, successfully reproduces key experimental observations. Furthermore, it reveals a fluctuating microphase separation, where the initial domain growth, following $t^{1/4}$ scaling, is eventually arrested, thereby shedding new light on the microscopic origins of unconventional phase separation of colloids in active liquids.