The helical nanofilament (HNF) liquid crystal (LC) phase of bent core mesogens (also commonly termed the B4 phase) is among the most unique and exotic LC phases known. The structure involves a spontaneous hierarchical self assembly of molecules leading to a supramolecular twisted rod structure with a square cross section approximately 30 nm on a side, with the length of the filaments unconstrained.
Based upon solid state NMR data, we have proposed that the helical nanofilaments actually represents an unusual assembly of organic crystalline nanoparticles, which form an LC phase, in the case of NOBOW existing in the temperature range between about 150°C and 110°C, which becomes a glass at temperatures below 110°C. That is, the HMF phase is not a typical molecular LC, but an LC of nanocrystals.
Descriptions of the structure of these nanoparticles, their LC phases, and approaches to alignment will be given. Also, the fascinating and potentially useful behavior of the HNF phase as a host for other materials (LC and non-LC) in nanostructured composites will be presented.
The helical nanofilament (HNF) liquid crystal phase is a member of an unusual class of thermotropic phases with lamellar structures dominated by a tendency towards developing negative Gaussian curvature of the layers. Members of this family are sometimes termed “dark conglomerates,” due to their behavior in polarized light microscopy. These include a fluid phases - the high temperature dark conglomerate phase, which is a kind of sponge phase, and the low temperature dark conglomerate phase, also seemingly a sponge phase with structural details currently under investigation. The HNF phase, also a “dark conglomerate,” seems to be unique in the family, since slow conformational dynamics indicate a quasi-crystalline structure within layers, but no long range positional correlations across layers. We have been exploring possible applications of the HNF phase, which is highly porous, as a host for the formation of alignable composites for photovoltaics and other organic semiconductor applications. Recent results regarding the structure of these composites, including data suggesting a remarkably elegant nanostructure for HNF-chiral nematic composites, will be discussed.