The focus of the Tsai research group is, for lack of a better explanation, “cooking up crazy stuff and seeing what it does.”
Liquid crystals (mesogens) are a wonderful niche of materials that can be found at the frontier of many disciplines within chemistry – everything from biochemistry to physical chemistry; and even then liquid crystals can be found everywhere from “origins of life” questions to advanced responsive materials (see: self-folding origami). Our research is probing the relationship between structure at the molecular level, and the function of the “supermolecular” ensemble. While the question is reasonably simple, and seemingly basic, it is still one that is largely unanswered by virtue of the fact that our usual means of predicting behavior relies on both empirical data (mountains of it!), and computational modeling (modeling 10k molecules absolutely with perfect precision is really hard!); and we don’t have nearly the amount of empirical data we wish we had, and computational models are far from perfect.
Currently, our research group is tackling a very interesting problem by dividing our efforts into two separate, but very convergent, approaches: taking systems with curvature, and then forcing splay into the system to cause significant frustration to the ability for the ensemble to retain their original means of dissipating twist and bend – hopefully allowing for interesting interfacially undulating and curved assemblies to manifest.
Tethered “nematic twin” mesogens are a relative new-comer to liquid crystals, though theoretical models predicted phases driven by twist-bend elastic forces well before mesogens manifesting those phases were reported in literature. Now known as nematic twist-bend (NTB) materials, these liquid crystals show a striking type of liquid-crystalline phase where coherent twist of the molecular long axis is paired with a coherent bend of the long axis director along a bulk heliconical axis. The heliconical phase shows striking phase textures (one is shown in the header image for this site!) and is a novel means of bulk curvature that appears to be an intermediate between traditional nematic liquid crystals (the stuff in your LCD TVs) and twisted cholesteric phases (seen commonly in natural materials like beetle shells). Our group is exploring the bounds of the mesophase space mapped out by these types of mesogenic structures by introducing incremental splay drive into the molecular structure in an attempt to create frustration between splay and the fundamental twist-bend ensemble.
Bent-core messages were first described electrooptically in literature in 1996, and the liquid crystal research community has been in love since then. These materials have shown spontaneous symmetry breaking in a fluid phase, incredible richness in phase assembly (to create a multitude of orthoconic, columnar, and lamellar arrangements), and potential applications for photonic and semiconductor devices. While bulk alignment is still difficult without significant effort (unlike their standard calamity cousins), there are a multitude of applications that do not require alignment, that these materials would excel in. Our group is exploring ways of increasing the frustration between crystallinity in the rigid aromatic cores and the isotropic drive of the alkyl tails, in an attempt to induce organization into either highly segregated lamellar systems, or dark conglomerate/sponge phases.