Smectic Demixing in the Phase Behavior and Self-Assembly of a Hydrogen-Bonded Polymer with Mesogenic Side Chains

Abstract

We present a detailed study of the structure and properties of a supramolecular complex formed via hydrogen bond association between poly(acrylic acid) chains and an imidazole-terminated biphenyl mesogen. The system exhibits a rich phase behavior as a function of temperature and stoichiometry, expressed as the molar ratio S between the number of mesogens and binding sites present. Smectic mesophases are formed for all S ≥ 0.033, a surprisingly small number. The dependence of the characteristic length scale of the mesophase on stoichiometry does not follow the expected 1-D swelling law. At low stoichiometries, S ≤ 0.2, the system exhibits little or no change in structure up to temperatures as high as 200 °C, beyond which changes become temperature irreversible. In contrast, at higher S, the system features complex thermally driven transitions among tilted monolayer and bilayer arrangements and complete, reversible isotropization of the system at elevated temperatures. Over a limited range of temperatures and compositions, a supramolecular length scale emerges that is well beyond the upper limit imposed by a bilayer construct and thus cannot be accounted for within the conventional paradigm. Binding isotherms reveal that the polymer has a limited capacity for the ligand with saturation occurring for S ≥ 0.33. These results suggest that the common assumption of homogeneously distributed tightly bound ligands with layer-like phase separation from the polymer backbone do not apply in this system over all compositions. The anomalous phase display is consistent with demixing between polymer rich and polymer poor domains due to the presence of excess unassociated mesogen, which can act as a solvent for the system.

Diblock copolymer–azobenzene complexes through hydrogen bonding: Self‐assembly and stable photoinduced optical anisotropy

“…1). This wavelength is intermediate between 1736 and 1705 cm −1 —the signals corresponding to the carbonyl stretching band of free and dimerized forms of the AZO, respectively—and supports the presence of hydrogen bonding interactions between complementary AZO carboxylic acid groups and vinylpyridine repeating units 46. While the main band in the carbonyl stretching region of P4VP(AZO) 0.75 is centred at 1711 cm −1 , it is also possible to distinguish a shoulder at higher wavenumbers.…”

Mesoporous Block Copolymer Nanoparticles with Tailored Structures by Hydrogen‐Bonding‐Assisted Self‐Assembly

“…Amphiphilic small molecules can hydrogen‐bond with one of the functional block of the copolymers, leading to the formation of comb‐like supramolecules which can further self‐assemble into hierarchical structure‐within‐structure morphologies 22–24. The supramolecular assemblies can be controlled by readily varying the molar ratio of small molecules to block copolymers which can regulate the volume fraction of the supramolecules.…”

Hydrogen bonding and liquid crystallinity of low molar mass and polymeric mesogens containing benzoic acids: a variable temperature Fourier transform infrared spectroscopic study

“…[3] This concept was extended by Kato, Fr echet and colleagues to consider liquid crystalline systems formed via hydrogen bonding between unlike hydrogen bond donors and acceptors such as benzoic acid and pyridyl-based fragments, respectively (see, for example, [6][7][8][9][10]). This material design approach has been very widely adopted and remains an area of considerable research activity; recent examples of hydrogen-bonded systems have included both main chain [11][12][13] and side chain liquid crystal polymers (SCLCPs), [14,15] and new discotic systems. [16][17][18] Hydrogen bonding also plays a key role in driving liquid crystalline behaviour in a diverse range of other materials including commercially important high-performance fibres, [19] protonic conductors [20,21] and liquid crystal sugars.…”