Square and Hexagonal Columnar Liquid Crystals Confined in Square and Triangular Pores

Abstract

Columnar liquid crystals confined in cylindrical pores are known to orient perpendicular to the pore axis, although for potential nanoelectronic applications they would need to be aligned axially. The X-ray diffraction study reveals that while in all three compounds examined, the columns arrange in concentric circles in circular pores, axial alignment is indeed achieved for the hexagonal phase of a discotic hexa-peri-hexabenzocoronene in "triangular pores," and for the square phase of a T-shaped amphiphile in "square pores." For the third compound, a carbazole dendron with very soft hexagonal columns, a new three-circle configuration is observed by atomic force microscopy (AFM) in triangular pores. The complex structure of domain walls in columnar liquid crystals is thus seen for the first time on the level of individual columns. A simple estimation of free energies confirms that it is the distortion of polygonal columnar lattice that prevents axial orientation in circular pores. The model also explains the appearance of the three-circle arrangement of soft columns.

Self-assembly of liquid crystals in nanoporous solids for adaptive photonic metamaterials

“…What drives this transition? As suggested by Ungar et al [30,46] it can be rationalised by the competition of the bending energy typical of the CC configuration and the energetic cost for the distortion of the 2D columnar lattice at the cylindrical pore wall in the case of the axial columnar state. Whereas the former scales linearly with the pore diameter d, the latter scales with log d. Thus, below a critical radius d c the axial state should be favoured compared to the radial one, in agreement with our observation.…”

“…However, given the edge-on surface anchoring they do not result from logpile structures, but from hexagonal arranged circular concentric bent columnar structures as illustrated in Figs. 3c and 7a-d(i) [30,47,49]. See also movie M4, where virtual and real scattering patterns are shown in direct comparison as a function of ω rotation for d=86 nm.…”

“…solid nanoporous material can guide the self-assembly and provides a mechanical stable, monolithic 3D scaffold structure [13]. However, because of spatial and topological constraints, the phase and self-assembly behaviour of confined soft matter and in particular confined LCs may substantially deviate from the bulk state [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”

“…An axial arrangement, see Fig. 3(d), which is of interest with respect to electronic applications, could only be achieved in DLCs with increased core-rigidity compared to HAT6 [49] or by non-circular channel cross-sections [30].…”

New Type of Columnar Liquid Crystal Superlattice in Double‐Taper Ionic Minidendrons

“…Such columns can be highly bendable, and circles of radius r down to the size of asingle molecule have been observed by high-resolution atomic force microscopy. [57] But in the case of Col 1 + 3 where neighbouring columns, in this case the major and minor columns, are connected by covalent linkers,t he outer circle with larger circumference is still restricted to containing the same number of mesogensa st he inner circle.C onsequently, the relative distortion in intermolecular spacing in two successive circular columns is Dc/c = d/r,w here d is the width of the column. Only for sufficientlyl arge r will the relative distortion be small enough for the cumulative energy of all distortions along the innermost loop of the s = 1 = 2 disclination to drop below the end energy of the bundle of straight but truncated columns in the middle (Inset 2o fFigure 3d).…”