Spontaneous demixing of chiral active mixtures in motility-induced phase separation

The demixing and sorting strategies for chiral active mixtures are crucial to the biochemical and pharmaceutical industries. However, it remains uncertain whether chiral mixed particles can spontaneously demix without the aid of specific strategies. In this paper, we investigate the demixing behaviors of binary mixtures in a model of chiral active particles to understand the demixing mechanism of chiral active mixtures. We demonstrate that chiral mixed particles can spontaneously demix in motility-induced phase separation (MIPS). The hidden velocity alignment in MIPS allows particles of different types to accumulate in different clusters, thereby facilitating separation. There exists an optimal angular velocity or packing fraction at which this separation is optimal. Noise (translational or rotational diffusion) can promote mixture separation in certain cases, rather than always being detrimental to the process. Since the order caused by the hidden velocity alignment in this process is not global, the separation behavior is strongly dependent on the system size. Furthermore, we also discovered that the mixture separation caused by MIPS is different from that resulting from explicit velocity alignment. Our findings are crucial for understanding the demixing mechanism of chiral active mixtures and can be applied to experiments attempting to separate various active mixtures in the future.