Separation of micron-sized dust particles in low-pressure air using a dusty plasma ratchet

The Feynman ratchet has the ability to convert random fluctuations into directional particle transport. The transport velocity of particles is highly dependent on their size, leading to directional transport and subsequent particle separation under suitable parameter conditions. Here, exploiting the distinct responses of particles with different sizes to the system, the separation of bi-dispersed dust particles is achieved experimentally in air at 35 Pa using a dusty plasma ratchet. To reveal the underlying mechanisms, we construct a plasma model and perform Langevin simulations for the particle separation. Our numerical results reveal that charged dust particles experience an asymmetric ratchet potential, which dictates their directional transport. Crucially, bi-dispersed dust particles are suspended at different heights and are subject to ratchet potentials with opposing asymmetries, resulting in their separation. These findings may offer new perspectives for related fields, including microfluidics, nanotechnology, and micrometer-scale particle manipulation.