Homeotropic and Planar Alignment of Discotic Liquid Crystals: The Role of the Columnar Mesophase

Abstract

Blends of two metal-free phthalocyanine mesogens exhibiting different mesophases (Col r phase from room temperature to isotropization for the first one, and Col r at room temperature then Col h from around 60 °C to isotropization for the second one) have been studied in order to determine the relationship between the type of mesophase and the alignment behavior. The phase diagram of this system has been built and evidence of full solid-state miscibility of the two pure constituents in all proportions and temperatures is presented. Investigation of phase alternation at room temperature as a function of composition revealed that border compositions exhibit Col r phases similar to the pure constituents, whereas Col h mesophase was stabilized for intermediate compositions. Combined polarized optical microscopy observations and X-ray diffraction measurements showed that homeotropic alignment is adopted only for mixed samples exhibiting Col h mesophase, thus demonstrating that the presence of a Col h mesophase is a necessary condition for homeotropic alignment.

Columnar Self‐Assembly in Electron‐Deficient Heterotriangulenes

“…Recently, Geerts and co-workers found that "just" a mesophase is necessary for this characteristic arrangement of the molecules. [30] This observation is in line with our study: compounds 5 and 6 show a LC phase, whereas 2, 3, and 4 are purely crystalline. We conclude from this series that the heterotriangulene-based discotics align homeotropically when an LC phase is present.…”

Miscibility in binary blends of non-peripheral alkylphthalocyanines and their application for bulk-heterojunction solar cells

“…In another study, each phthalocyanine derivative has different HOMO, LUMO level, nevertheless, the charge carrier mobilities of binary mixtures composed of the compounds was almost maintained that of each material [22]. On the other hand, molecular alignment control of mixed materials has been reported [23]. It is possible for the binary mixture composed of phthalocyanine derivatives with different alkyl substituents to continuously control the lattice parameter and the phase transition from Col r phase to Col h phase as a function of the mixture ratio.…”

Synthesis and thermotropic behavior of side chain polysiloxane bearing triphenylene moiety

“…In this organization, the molecules are face-on arranged on the surface with their columnar axis perpendicular to the substrate. This leads to the lack of birefringence in polarized light for typically a dendritic morphology of the LC phase [34][35][36]. We observed in TOA characteristic textures for this type arrangement [21] ( Figure 4 -image 5) indicating a strong interaction with the substrate (Figure&4b).…”