Crystallization of orientationally ordered matter

Existing theories of nucleation and growth implicitly assume crystallization occurs from an isotropic parent phase. Polymorphic phase transitions, the solidification of natural (e.g. silk) and synthetic polymers (e.g. Kevlar), and the crystallization of vapor-deposited glasses are just some examples of transformations wherein crystals emerge out of orientationally anisotropic media. Yet, the influence of parent phase anisotropy on crystallization phenomenon remains largely unexplored both from experimental and theoretical standpoints. In this review, we propose that small-molecule liquid crystals are suitable model systems for understanding the role of orientational anisotropy of the precursor phase on crystallization. For small-molecule mesogens, both the LC parent and daughter crystal phases can be organized into single-domain states, where molecular packing can be precisely controlled and determined. Early progress in understanding crystallization of small-molecule liquid crystals is reviewed and outstanding problems in the field are identified. A deeper understanding of the role of anisotropic molecular orientation on crystallization could enable fundamentally new methods to control crystal texture and polymorph selection. Control over these crystallization outcomes is of interest to a diverse range of fields, from pharmacology to organic electronics.