Realization of hydrodynamic experiments on quasi-2D liquid crystal films in microgravity

Abstract

Freely suspended films of smectic liquid crystals are unique examples of quasi two-dimensional fluids. Mechanically stable and with quantized thickness of the order of only a few molecular layers, smectic films are ideal systems for studying fundamental fluid physics, such as collective molecular ordering, defect and fluctuation phenomena, hydrodynamics, and nonequilibrium behavior in two dimensions (2D), including serving as models of complex biological membranes. Smectic films can be drawn across openings in planar supports resulting in thin, meniscus-bounded membranes, and can also be prepared as bubbles, either supported on an inflation tube or floating freely. The quantized layering renders smectic films uniquely useful in 2D fluid physics. The OASIS team has pursued a variety of ground-based and microgravity applications of thin liquid crystal films to fluid structure and hydrodynamic problems in 2D and quasi-2D systems. Parabolic flights and sounding rocket experiments were carried out in order to explore the shape evolution of free floating smectic bubbles, and to probe Marangoni effects in flat films. The dynamics of emulsions of smectic islands (thicker regions on thin background films) and of microdroplet inclusions in spherical films, as well as thermocapillary effects, were studied over extended periods within the OASIS (Observation and Analysis of Smectic Islands in Space) project on the International Space Station. We summarize the technical details of the OASIS hardware and give preliminary examples of key observations.

Freely suspended smectic films with in-plane temperature gradients

“…It is difficult to estimate the resulting temperature profile in the chamber, so that we can provide only a qualitative discussion of the observed phenomena shown in figure 4. The material used was a smectic A mixture (8CB + Displaytech MX 12160 [31]), with phase sequence Isotropic 56°C Nematic 54°C SmA 5°C Cryst. The uniformly thin bubble with a film thickness of a few smectic layers (10-20 nm) was first decorated with small islands (approximately 80 nm thick), which were created using airjets [31].…”

“…The material used was a smectic A mixture (8CB + Displaytech MX 12160 [31]), with phase sequence Isotropic 56°C Nematic 54°C SmA 5°C Cryst. The uniformly thin bubble with a film thickness of a few smectic layers (10-20 nm) was first decorated with small islands (approximately 80 nm thick), which were created using airjets [31]. Then the needle temperature was set to 40°C, with a nominal background temperature of the chamber walls of 28°C.…”

“…Marangoni flow in the opposite direction, towards the supporting needle, was achieved by setting that needle to the chamber temperature and heating the two metal airjet needles at the opposite pole of the smectic bubble [31]. Selected images of this experiment are shown in figure 7.…”

“…Transport processes in thin smectic films driven by thermal gradients have also been investigated in microgravity (μg) experiments on the International Space Station ISS [31]. Smectic bubbles about 15mm in diameter and with film thicknesses of a few nanometers were created on a thin support needle 1.27mm in diameter.…”

Liquid Crystals

“…My own work involves collaborators not only in the United States, but in Canada, France, Slovenia, and Israel. In fact, liquid crystal research has gone beyond the globe, with several experiments requiring microgravity having been performed aboard the International Space Station [9], and at least three more planned for the near future. In addition to the regular stream of liquid crystal-related papers appearing in Crystals, the section is organizing two exciting special issues.…”