Structural complexity driven by liquid–liquid crystal phase separation of smectics

Many phase separated systems-including industrial nanocomposites, biomaterials, and cellular condensates-can form dispersed droplets that exhibit internal liquid crystalline ordering. The elasticity of the internal liquid crystalline mesophase often reshapes the droplet geometry, resulting in structures such as filaments, tactoids, tori, and surface facets. Our recent work demonstrated that by slowly cooling into the binodal from a well-mixed state, the dynamics of this liquid-liquid crystal phase separation (LLCPS) can give rise to striking filamentous networks of smectic condensates. Here, we investigated how choice of mesogen, solvent, and concentration can dramatically alter these networks. Using X-ray scattering, we observed that the solvent swells the smectic layers, seemingly reducing the smectic layer's bend modulus, altering the geometric structure of the network. Consistent with this interpretation, samples with a higher smectic layer swelling exhibited more geometrically-complex structures that require higher smectic layer bending to form. We further demonstrated that the formation of filaments and networks does not occur in all systems exhibiting coexistence of a smectic and isotropic phase. Instead, we only observed filament and network formation when the smectic phase developed directly from the isotropic phase-further highlighting the importance of path-dependence in forming these non-equilibrium structures. These results demonstrate some of the structural diversity of dispersed droplet geometries that can be accessed by LLCPS, and elucidate some of the requisite conditions for them to form networked morphologies.