Liquid Crystal Properties of Microgravity Dusty Plasma

In this work we demonstrate that microgravity dusty plasmas exhibit various properties of the liquid crystalline state of matter, such as alignment along common director axis, layering transitions, and pattern formation. This study combines analysis of data from the Plasmakristall-4 (PK-4) facility on board the International Space Station (ISS) with predictions from many-body simulations and analytical calculations. Previous ISS experiments have shown that microgravity dusty plasmas can undergo a transition from homogeneous liquid to a filamentary solid, reminiscent of the one occurring in electrorheological colloidal suspensions. However, our analysis suggests that the filamentary dusty plasmas in PK-4 transition to a mesophase intermediate between liquid and solid, i.e., a liquid crystalline phase. 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 findings, we discuss how microgravity filamentary dusty plasmas can be used to study fundamental open questions related to universality of phase transitions, pattern formation, and defect propagation in liquid crystals.