# Driving force for a nonequilibrium phase transition in three dimensional complex plasmas

## TL;DR

This paper investigates the non-equilibrium phase transition in three-dimensional complex plasmas, focusing on lane formation driven by particle size and ion mean free path effects under microgravity conditions.

## Contribution

It introduces a model explaining the driving force behind lane formation, highlighting the role of ion mean free path dependence on particle density and size.

## Key findings

- Driving force depends on particle size and ion mean free path.
- Force changes sign when probe and dust particles are equal in size.
- Model aligns with experimental observations of particle motion.

## Abstract

An example of the non-equilibrium phase transition is the formation of lanes when one kind of particles is driven against the other. According to experimental observation, lane formation in binary complex plasmas occurs when the smaller particles are driven through the stationary dust cloud of the larger particles. We calculate the driving force acting on a probe particle that finds itself in a quiescent cloud of particles in complex plasma of the low-pressure radio frequency discharge under microgravity conditions. It is shown that the nonzero driving force is a result of the dependence of the ion mean free path on the particle number density. If this effect is properly included in the model of similar complex plasmas then one arrives at the driving force that changes its sign at the point where the probe and the dust particles have equal radii. If the probe is smaller than the dust particle then the driving force is directed toward the discharge center and vice versa, in accordance with experiment. Obtained results can serve as the ansatz for future investigation of the lane formation in complex plasmas.