期刊
ACS NANO
卷 9, 期 2, 页码 1759-1766出版社
AMER CHEMICAL SOC
DOI: 10.1021/nn506605p
关键词
columnar liquid crystals; discotics; confinementS anodic aluminum oxide; nanopores; orientation; rigidity; AFM; X-ray diffraction; SAXS; GISAXS; disclinations
类别
资金
- NSF-EPSRC PIRE project RENEW (EPSRC) [EP_K034308]
- Leverhulme Foundation [RPG-2012-804]
- 1000 Talents program of the Government of China
- NSF [DMR-1066116, DMR-1120901, OISE-1243313]
- P. Roy Vagelos Chair at Penn
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1066116] Funding Source: National Science Foundation
- Office Of Internatl Science &Engineering
- Office Of The Director [1243313] Funding Source: National Science Foundation
- EPSRC [EP/G032726/1, EP/K034308/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/K034308/1, EP/G032726/1] Funding Source: researchfish
Axial orientation of discotic columnar liquid crystals in nanopores of inorganic templates, with the columns parallel to the axis of the nanochannels, is considered desirable for applications such as production of molecular wires. Here, we evaluate experimentally the role of the rigidity of the LC columns in achieving such orientation in nanopores where the planar anchoring (i.e., columns parallel to wall surface) is enforced. We studied the columnar phase of several discotic compounds with increasing column rigidity in the following order: dendronized carbazole, hexakis(hexyloxy)triphenylene (HAT6), a 1:1 HAT6-trinitrofluorenone (TNF) complex, and a helicene derivative. Using 2-D X-ray diffraction, AFM, grazing incidence diffraction, and polarized microscopy, we observed that the orientation of the columns changes from circular concentric to axial with increasing column rigidity. Additionally, when the rigidity is borderline, increasing pore diameter can change the configuration from axial back to circular. We derive expressions for distortion free energy that suggest that the orientation is determined by the competition between, on the one hand, the distortion energy of the 2-d lattice and the mismatch of its crystallographic facets with the curved pore wall in the axial orientation and, on the other hand, the bend energy of the columns in the circular configuration. Furthermore, the highly detailed AFM images of the core of the disclinations of strength +1 and +1/2 in the center of the pore reveal that the columns spiral down to the very center of the disclination and that there is no amorphous or misaligned region at the core, as suggested previously.
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