Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

Abstract

This work describes the dilute solution and solid-state structure of polyelectrolyte complexes generated from hyperbranched polylysine (HBPL) and various anionic, sodium alkyl sulfate surfactants. In dilute solution, the radius of gyration (R g ) of the HBPL and HBPL-surfactant complexes was determined in the Guinier regime in good solvent conditions by means of small-angle X-ray scattering (SAXS). With increasing molecular weight of the HBPL, an increase in R g up to a maximum of 3.7 and 4.2 nm was observed for the HBPLs and HBPL-surfactant complexes, respectively. In the solid state, HBPL-surfactant complexes were found to form liquid crystalline (LC) phases, whose thermal stability and structure depended both on the molecular weight of the HBPL as well as on the nature of the anionic surfactant. Depending on the surfactant alkyl chain length, liquid crystalline phases with short range liquid-like order, columnar hexagonal packing or lamellar ordering were observed. By combination of small-angle X-ray scattering, differential scanning calorimetry (DSC), and cross-polarized light optical microscopy (CPOM), the exact structure of the LC phases, as well as their region of thermal stability, could be identified. HBPL-sodium dodecyl sulfate LC phases showed thermotropic behavior and underwent two transitions with increasing temperature. First, at lower temperatures, an order-nematic transition was observed. Upon further temperature increase, a second transition from a nematic to an isotropic phase was observed. Structural models for these different LC phases are proposed.

Controlling Hierarchical Self-Assembly in Supramolecular Tailed-Dendron Systems

“…A delay between the melting of the alkyl tails and the clearing of the lamellar phase has, however, been found by the same authors for hyperbranched polypeptides supramolecularly complexed to alkyl ionic tails. 44 We believe that in the present case, as in ref 42, either the uncorrelation or the simultaneous occurrence of order-order transitions and alkyl tail melting observed for G2-PMeDEG 33 -C 18 SO 4 and G2-PMeDEG 26 -C 18 SO 4 may be related to: (i) the volume fraction of the alkyl tails themselves and (ii) to whether the hierarchical lamellar organization is the most stable morphology when the constraints imposed by the crystalline alkyl tails are released upon melting. In support of this scenario, for G2-PMeDEG 26 -C 18 SO 4 , where the volume fraction of surfactant and dendron is 0.26 (0.74 polymer), the lamellar structure is maintained when the crystallinity of alkyl tails melts; on the contrary, for G2-PMeDEG 33 -C 18 SO 4 , where the volume fraction is 0.22 (0.78 polymer), the stable phase upon suppression of alkyl tail crystallinity becomes the core-shell columnar hexagonal.…”

Self‐Assembly and Dynamics of Polypeptides

“…[75] Below we review some recent work on the self-assembly and dynamics of peptide-functionalized polyphenylene cores.…”

Mesogenic Structures, Lyotropic and Thermotropic Phase Transitions in Demethyl-Ionene Alkyl Sulfonate Complexes

“…So the first six reflections (hk) were all present, and their positions should satisfy the equation q 10 :q 11 :q 20 :q 21 :q 30 :q 22 = 1:√3:2:√7:3:√12. We observe a broad (11) reflection at √3 q 10 , that predominates the IMAXS pattern and might hide a smaller (20) scattering maximum next to it. There is no sign of a (21) reflection, corresponding to the ratio √7.…”