We employ reactive dynamical density functional theory (R-DDFT) and reactive Brownian dynamics (R-BD) simulations to study the non-equilibrium structure and phase behavior of an active dispersion of soft Gaussian colloids with binary interaction switching, i.e., we consider a one-component colloidal system in which every particle can individually switch stochastically between two interaction states (here, sizes ‘big’ and ‘small’) at predefined rates. We consider the influence of switching activity on the inhomogeneous density profiles of the colloids confined by various external potentials, as well as on their pair structure and phase behavior in bulk solutions. For the latter, we extend the R-DDFT method to incorporate the Percus test-particle route. Our results demonstrate that switching activity strongly modifies the steady-state density profiles and structural (pair) correlations. In particular, the switching rate interpolates from a near-equilibrium binary colloidal mixture of two states at very low rates to a non-equilibrium, ‘one-state liquid’ at very high rates characterized by one, average interaction size. The latter limit can be described by an equivalent effective one-component (EOC) equilibrium system, for which the exact analytical expression for the effective pair potential is a diffusion-weighted superposition of the active systems' pair potentials. This leads to the interesting fact that under certain conditions an interacting switching system can behave like a non-interacting (ideal) gas in the limit of high switching rates. Moreover, for colloids that are unstable (i.e., demix) near equilibrium, we demonstrate that phase separation and micro-clustering in both confinement and bulk can be dynamically controlled by the switching rate, and vanish for high rates. All R-DDFT results are in excellent agreement with our R-BD simulations.

中文翻译：

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软胶体的主动二元切换：稳定性和结构特性

我们采用反应动力学密度泛函理论 (R-DDFT) 和反应布朗动力学 (R-BD) 模拟来研究具有二元相互作用切换的软高斯胶体的主动分散的非平衡结构和相行为，即，我们考虑一个单组分胶体系统，其中每个粒子都可以在两个相互作用状态（这里，尺寸“大”和“小”）之间以预定义的速率单独随机切换。我们考虑了开关活动对受各种外部电位限制的胶体的不均匀密度分布的影响，以及它们在体溶液中的对结构和相行为的影响。对于后者，我们扩展了 R-DDFT 方法以合并 Percus 测试粒子路线。我们的结果表明，开关活动强烈地改变了稳态密度剖面和结构（对）相关性。特别是，转换速率从两种状态的接近平衡的二元胶体混合物以非常低的速率插入到非平衡的“单态液体”中，具有非常高的速率，其特征在于：平均交互大小。后一个限制可以通过等效有效单组分 (EOC) 平衡系统来描述，其中有效对电位的准确解析表达式是活性系统对电位的扩散加权叠加。这导致了一个有趣的事实，即在某些条件下，相互作用的开关系统在高开关速率的限制下可以表现得像非相互作用（理想）气体。此外，对于不稳定的胶体（这导致了一个有趣的事实，即在某些条件下，相互作用的开关系统在高开关速率的限制下可以表现得像非相互作用（理想）气体。此外，对于不稳定的胶体（这导致了一个有趣的事实，即在某些条件下，相互作用的开关系统在高开关速率的限制下可以表现得像非相互作用（理想）气体。此外，对于不稳定的胶体（ie , demix) 接近平衡，我们证明了限制和体积中的相分离和微团簇可以由开关速率动态控制，并且在高速率时消失。所有 R-DDFT 结果与我们的 R-BD 模拟非常吻合。