Memory effects from topological connectivity of nematic liquid crystals confined in porous materials

It is known that confinement of nematic liquid crystals (NLC) into porous structures gives rise to systems having strong and intriguing memory effects. Some work has been done on NLC hosting nanostructured gels, but a general understanding of these effects is still missing. Prompted by experimental results, we have studied by computer simulation, the behavior of NLC confined in porous media with various bicontinuous geometries and providing perpendicular anchoring of the nematic director at their surface. We find that in all structures, frustration induced by the conflicting boundary conditions induces the formation of disclination defect lines that are stabilized by the very geometry of the porous media. Various sets of defect arrangements are possible, a property that makes the system highly metastable and capable of memorizing the alignment forced by external fields. We determine which geometrical features of the porous matrices maximize metastability and how they affect the dynamics of NLC. We provide the basics for designing NLC-based heterogeneous structures targeting specific electro-optical properties.