Structure and Phase Behavior of a Discotic Columnar Liquid Crystal Confined in Nanochannels

The confinement of discotic columnar liquid crystal in nanoporous templates is a promising strategy to design nanofibers with potential applications in organic electronics. However, for many materials, geometric nanoconfinement has been shown to induce significant modifications of the physical properties, such as structure or phase behavior. We address the case of a discotic columnar liquid crystal confined in various templates. The influence of the size, the roughness, and the chemical nature of pores was investigated for a pyrene derivative by small-angle neutron scattering, X-ray diffraction, and calorimetry on a wide range of temperatures. A homeotropic anchoring (face-on orientation of the disk-shape molecules at the interface) is favored in all smooth cylindrical nanochannels of porous alumina while surface roughness of porous silicon promotes more disordered structures. The hexagonal columnar isotropic phase transition is modified as a result of geometrical constraints and interfacial interactions.