Microgravity Dusty Plasmas Exhibit Properties Of Liquid Crystals

Abstract

This study examines structure and stability of filamentary dusty plasmas using data from the Plasmakristall-4 (PK-4) facility on board the International Space Station. Microgravity dusty plasmas have been observed to form extended field-aligned filaments in the DC discharge of the PK-4 experiments, which have been compared to the filamentary state in electrorheological (ER) fluids. Here we show that analysis of the filamentary state of dusty plasma suggests that meaningful comparisons can be made between these microgravity structures and liquid crystals (LCs) with rod-shaped molecules. Specifically, we demonstrate that the coupling between dust particles within filaments is crystal-like, while the coupling across filaments is liquid-like. In addition to a common orientation along a director axis (nematic behavior), the dust filaments also appear to align in large-scale nested structures, or shells (smectic behavior). Finally, the dust filaments are found to arrange in hexagonal patterns in the plane perpendicular to their director axis, suggesting the possibility of a smectic-B or smectic-C state. Based on these observations, we will argue that microgravity filamentary dusty plasmas can be used to study universality of phase transitions and pattern formation in liquid crystals.