Straining soft colloids in aqueous nematic liquid crystals
Significance Liquid crystals (LCs) are anisotropic, viscoelastic fluids that can be used to direct colloids (e.g. metallic nanorods) into organized assemblies with unusual optical, mechanical, and electrical properties. In past studies, the colloids have been sufficiently rigid that their individual shapes and properties have not been strongly coupled to elastic stresses imposed by the LCs. Herein, we explore how soft colloids (micrometer sized shells formed from phospholipids) behave in LCs. We reveal a sharing of strain between the LC and shells, resulting in formation of spindle like shells and other complex shapes and also, tuning of properties of the shells (e.g. barrier properties) These results hint at previously unidentified designs of reconfigurable soft materials with applications in sensing and biology. Liquid crystals (LCs) because of their long range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2 50 um) into two distinct populations of GUVs with spindle like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r 1.54, where R and r are the major and minor radii, respectively) consistent with an LC elasticity induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 R/r 10) that arise from an efflux of LCs from the GUVs during the shape transformation, consistent with LC induced straining of the membrane leading to transient membrane pore formation. A thermodynamic analysis of both populations of GUVs reveals that the final shapes adopted by these soft colloids are dominated by a competition between the LC elasticity and an energy ~0.01 mN/m) associated with the GUV LC interface. Overall, these results provide insight into the coupling of strain in soft materials and suggest previously unidentified designs of LC based responsive and reconfigurable materials.
Proceedings of the National Academy of Sciences