We study binary mixtures of small active and big passive athermal particles interacting via soft repulsive forces on a frictional substrate. Athermal self propelled particles are known to phase separate into a dense aggregate and a dilute gas-like phase at fairly low packing fractions. Known as motility induced phase separation, this phenomenon governs the behaviour of binary mixtures for small to intermediate size ratios of the particle species. An effective attraction between passive particles, due to the surrounding active medium, leads to true phase separation for large size ratios and volume fractions of active particles. The effective interaction between active and passive particles can be attractive or repulsive at short range depending on the size ratio and volume fractions of the particles. This affects the clustering of passive particles. We find three distinct phases based on the spatial distribution of passive particles. The cluster size distribution of passive particles decays exponentially in the homogeneous phase. It decays as a power law with an exponential cutoff in the clustered phase and tends to a power law as the system approaches the transition to the phase separated state. We present a phase diagram in the plane defined by the size ratio and volume fraction of passive particles.

中文翻译：

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主动和被动粒子的二元混合物的相分离

我们研究了小主动和大被动无热粒子的二元混合物，它们通过摩擦基底上的软排斥力。已知无热自推进颗粒在相当低的填充分数下相分离成致密的聚集体和稀的气相样相。这种现象被称为运动引起的相分离，这种现象支配了二元混合物在小到中等尺寸比率的颗粒物种中的行为。由于周围的活性介质，无源颗粒之间的有效吸引导致了大尺寸比例和体积分数的活性颗粒发生真正的相分离。主动和被动粒子之间的有效相互作用在短范围内可能是吸引或排斥的，具体取决于粒子的尺寸比和体积分数。这会影响无源粒子的聚集。基于无源粒子的空间分布，我们发现了三个不同的阶段。无源粒子的团簇尺寸分布在均匀相中呈指数衰减。它在聚集相中作为幂函数衰减且具有指数截止值，并在系统接近过渡到相分离状态时趋于幂定律。我们在由无源粒子的尺寸比和体积分数定义的平面中呈现相图。