Activity at director gradients in living liquid crystals and in liquid crystal elastomers
Tuesday, January 16, 2018 - 9:00am - 9:50am
Self-propelled bacteria are marvels of nature. If we can control their dynamics, we could use it to power microsystems of the future. Unfortunately, bacteria swim mostly randomly in isotropic liquids such as water. It is difficult to control their dynamics by factors other than transient gradients of nutrients; visual, acoustic and tactile communication channels that humans use to control large animals are not effective. To establish communication, we replace water with a water-based lyotropic liquid crystal, which couples propulsion of bacteria to the orientational order of the medium. The long-range orientational order of the liquid crystal can be designed as uniform or be pre-patterned into various structures by a photoalignment technique. The pre-imposed patterns of liquid crystal orientation allow one to gain a significant control over the dynamics of bacteria, namely, their trajectories, polarity of swimming, spatial variation of concentration. The mechanism is rooted in the coupling of the activity and spatial gradients of the director. A similar coupling can be observed in a system that is at first sight very different from living liquid crystals, namely, in liquid crystal elastomers with pre-patterned director. Thermal expansion of the elastomer coatings result in a dynamic surface profile that is deterministically connected to the in-plane director gradients. The work is supported by NSF grants DMR-1507637 and DMS-1729509.