Self-shaping liquid crystal droplets by balancing bulk elasticity and interfacial tension

Abstract

The shape diversity and controlled reconfigurability of closed surfaces and filamentous structures, universally found in cellular colonies and living tissues, are challenging to reproduce. Here, we demonstrate a method for the self-shaping of liquid crystal (LC) droplets into anisotropic and three-dimensional superstructures, such as LC fibers, LC helices, and differently shaped LC vesicles. The method is based on two surfactants: one dissolved in the LC dispersed phase and the other in the aqueous continuous phase. We use thermal stimuli to tune the bulk LC elasticity and interfacial energy, thereby transforming an emulsion of polydispersed, spherical nematic droplets into numerous, uniform-diameter fibers with multiple branches and vice versa. Furthermore, when the nematic LC is cooled to the smectic-A LC phase, we produce monodispersed microdroplets with a tunable diameter dictated by the cooling rate. Utilizing this temperature-controlled self-shaping of LCs, we demonstrate life-like smectic LC vesicle structures analogous to the biomembranes in living systems. Our experimental findings are supported by a theoretical model of equilibrium interface shapes. The shape transformation is induced by negative interfacial energy, which promotes a spontaneous increase of the interfacial area at a fixed LC volume. The method was successfully applied to many different LC materials and phases, demonstrating a universal mechanism for shape transformation in complex fluids.

Growth of Myelin Figures from Parent Multilamellar Vesicles

“…As the myelins grow over time, the boundaries of the parent MLVs remain unchanged, in contrast to the continuously growing diameters of other MLVs in the solution (Figure b). Similar growth of isolated long tubular filaments upon cooling has been occasionally observed in suspensions of liquid-crystalline droplets. ,− In this work, we show that the growth rate of such out-of-equilibrium tubular lamellar structures is controlled by the thermodynamic equilibrium of I + LC phases and occurs through the rearrangement of surfactant molecules from the source micellar self-assemblies into the lamellar structures. We use NaLAS as a model system here because it permits the spontaneous formation of MLVs in the absence of extra additives; however, the growth mechanisms discussed here can explain the kinetics of myelin growth in other systems of mixed surfactants and phospholipids. ,, …”

Run-and-halt motility of droplets in response to light

“… 41 One recent research reports that droplets can change shape in response to a temperature-induced decrease in interfacial tension. 42

Figure 2 Insights into the run-and-halt behavior of droplets (A) Trajectory of an oil droplet in a 2 mM trans -azobenzene aqueous solution. The trajectory corresponds to 17 min of movement.

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“…In recent work, a small decrease in interfacial tension was proven sufficient to modify the shape of liquid crystal droplets substantially. 42 , 49 …”

Focal conic flowers, dislocation rings, and undulation textures in smectic liquid crystal Janus droplets

“…For decades, these anisotropic soft materials have yielded surprises, including delicate textures, complex phase behavior, and unusual packings within drops. [1][2][3][4][5][6][7][8] Some current interest centers on experiments that confine LCs in tiny ''containers'' with controllable geometry and boundary conditions. These scenarios offer novel playgrounds to probe fundamental questions about LC assembly and response to frustration.…”