Design of Liquid Crystalline Block Molecules with Nonconventional Mesophase Morphologies:  Calamitic Bolaamphiphiles with Lateral Alkyl Chains

Abstract

Novel bolaamphiphiles, consisting of a biphenyl rigid core, polar 2,3-dihydroxypropoxy groups at each terminal end, and an additional long alkyl chain in a lateral position have been synthesized. The structures of these ternary block molecules were systematically changed by variation of the length and position of the alkyl chain, by introduction of additional spacer units between one of the 2,3-dihydroxypropyl groups and the rigid core, and by replacement of one of the 2,3-dihydroxypropoxy groups by a single hydroxy group. The influence of these structural variations on the liquid crystalline properties of these new materials was investigated by polarized-light microscopy, differential scanning calorimetry, and X-ray diffraction. These investigation have shown that, by elongation of the lateral chain, a transition from a smectic monolayer structure (SmA 1 ) via a strongly distorted layer structure (SmA + ), a centered rectangular columnar phase (Col r /c2mm) and a noncentered rectangular columnar phase (Col r /p2gg) to a hexagonal columnar phase (Col h /p6mm) takes place. Elongation of the bolaamphiphilic core leads to the loss of the columnar phases, which are replaced by smectic phases, whereas reduction of its length favors the hexagonal columnar phase. This phase sequence is explained as a result of the microsegregation of the lateral alkyl chains from the rigid aromatic cores. The segregated alkyl chains are organized in columns that interrupt the smectic layers. The hydrogen bonding keep the bolaamphiphilic cores fixed end to end, so that they form networks of cylinders around the lipophilic columns. The space required by the alkyl chains with respect to the length of the bolaamphiphilic cores is restricted and largely determines the geometry of the cylinders, which leads to the observed phase sequence. The obtained mesophase morphologies, built up by three distinct sets of subspaces, are related to morphologies of some ternary block copolymers. Furthermore, the investigated compounds represent a novel class of materials, capable of forming supramolecular columnar mesophases.

Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene) Cores on Self-Assembly Behaviour. Part 1: Transition between Amphiphilic and Polyphilic Self-Assembly in the Bulk

“…Depending on the ratio between chain volume and space available in the prismatic cells (mainly determined by the length of the rod-like units), the cross-sectional shape of the prismatic cells changes. As observed experimentally [10][11][12][13][14][15][16][17] and supported by simulations [18][19][20][21], there is a transition from rhombic or triangular via square, pentagonal to hexagonal cells with growing lateral chain volume or with decreasing rigid core length. Occasionally, complex tiling patterns composed of cells with different shapes were found [22], especially if different lateral chains (e.g., fluorinated and further increased volume, giant honeycombs (Figure 1i-k) [25][26][27] and lamellar phases with coplanar organization of rods (Lam) (Figure 1l-n) were observed [28][29][30][31].…”

“…In the SAXS pattern, there is an additional diffuse scattering around 2θ ~ 2-3° (see Figure 13c), corresponding to a mean distance of ~4.4 nm, which could indicate a partial separation of the RF and RH chains from the rod-like OPE cores into distinct domains with short range correlation. This kind of SmA+ phase (see Figure 1b) with diffuse small angle scatterings and very weak layer reflection has previously been observed for lamellar phases of polyphiles close to the crossover to the organization in honeycombs [11,12]. Figure S2); abbreviations: SmA+ lamellar phase with short range correlation of the nano-segregated domains of the lateral chains (see Figure 1b) for other abbreviations, see Figure 2; numerical XRD data are collated in Table S3, for calculation of nwall, see Table S6; b Enthalpy involves both transitions, and the sample immediately crystallizes during formation of the SmA+ phase.…”

“…In the SAXS pattern, there is an additional diffuse scattering around 2θ~2-3 • (see Figure 13c), corresponding to a mean distance of~4.4 nm, which could indicate a partial separation of the R F and R H chains from the rod-like OPE cores into distinct domains with short range correlation. This kind of SmA+ phase (see Figure 1b) with diffuse small angle scatterings and very weak layer reflection has previously been observed for lamellar phases of polyphiles close to the crossover to the organization in honeycombs [11,12]. by alternating non-polar layers involving the aromatic cores, the alkyl chains, and the RF segments and polar layers involving the disordered EO chains and the glycerols.…”

Novel Phase Morphologies in a Microphase-Separated Dendritic Polymer Melt

“…We employ a numerical solution of the SCFT equations (eq [13][14][15][16][17][18][19] to evaluate the canonical ensemble free energies for various candidate inhomogeneous phases in their unit cells. Initial field configurations are seeded in order to produce a unit cell of a given mesophase, and the modified diffusion equation (eq 9) is solved pseudospectrally with an operator splitting scheme.…”

Simulation of bulk phases formed by polyphilic liquid crystal dendrimers

“…In one sense the simplest polyphilic mesogens are linear or star-shaped ABC triblock copolymers, which undergo microphase separation to produce interesting mesophase structures [1][2][3][4].However, the range of molecular architectures possible are limited only by the ingenuity of chemists. Recent interesting examples include the use of calamitic bolaamphiphiles with a rigid rod-like aromatic unit, two hydrophilic terminal groups, and a liphophilic or semifluorinated lateral alkyl chain [5][6][7]; and the use of 'Janus molecules' with two groups of differing mesogens tethered to a molecular core via semi-flexible spacers [8].…”