Calamitic Bolaamphiphiles with (Semi)Perfluorinated Lateral Chains:  Polyphilic Block Molecules with New Liquid Crystalline Phase Structures

Abstract

Novel bolaamphiphiles consisting of a rigid biphenyl unit, two terminal polar 1,2-diol units and laterally attached (semi)perfluorinated chains have been synthesized via palladium-catalyzed cross coupling reactions as the key step. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light optical microscopy, DSC, and X-ray scattering, and the influences of the length, number, structure, and position of the lateral chain on the mesomorphic properties were studied. A wide variety of unique liquid crystalline phases were found upon elongation of the lateral semiperfluorinated chains. For short- and medium-chain length a series of columnar phases were observed, and upon further elongation of the lateral chain a series of novel mesophases with layer structures were found. In the columnar phases, the nonpolar lateral chains segregate into columns, which are embedded in honeycomb-like networks of cylinders consisting of the biphenyl units. Strings of hydrogen-bonding networks of the diol groups provide cohesive forces, which maintain the overall structure. Changing the length of the lateral chains influences the diameter of the columns and thus determines the number of biphenyl units which are required to surround these columns. The number of these units [four (c2mm, p4mm), five (p2gg), six (p6mm), eight (c2mm) or 10 (p2gg)] defines the shape of the cylinders as well as the lattice type of the columnar phase. It is proposed that the columnar phases with a p2gg lattice result from the regular organization of pairs of cylinders which have a pentagonal cross sectional shape. In the mesophases with layer structure the aromatic rodlike cores are arranged parallel to the layer planes, and the onset of orientational and positional ordering of the biphenyl segments leads to a sequence of subtypes for these lamellar phases (Lam(Iso)-Lam(N)-Lam(X)).

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 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.…”

“…Prominent examples of these laterally substituted compounds are T-shaped and X-shaped bolapolyphiles composed of a rod-like π-conjugated core, terminally functionalized by hydrogen bonding glycerol groups at each end, and carrying one (T-shaped) [11,12] or two lipophilic lateral chains at opposite sides of the rod-like unit (X-shaped) [13]. These flexible lateral chains cause a frustration of the layer-like organization for steric reasons (Figure 1a,b).…”

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].…”