Polymer conformation in supramolecular complexes with wedge-shaped ligands: Exploring the impact of the liquid-crystalline organization

International audienceThe chain conformation of poly(2-vinylpyridine) (P2VP) complexed by 4-((4-((3,4,5-tris(dodecyloxy)benzoyl)oxy)phenyl)diazenyl)benzenesulfonic acid at different degrees of neutralization (DN) was addressed by small- and wide-angle neutron scattering technique. To get information on the conformation of P2VP chains spatially confined within lamellar and columnar mesophases at different DNs, the complexes were prepared from a blend of protonated and deuterated P2VP. The 2D scattering patterns of extruded fibers show that at low DN the complex self-organizes in a lamellar phase. The inertial mean distances in the direction parallel and perpendicular to the fiber axis reveal the formation of compact disc-like globules of individual P2VP chains at DN = 25 and 33%. With the increase of DN the interaction between the neighboring side groups along the backbone increases. This results in formation of hexagonal columnar phase at DN = 50%, in which the P2VP macromolecules are confined within cylindrical channels forming most probably a disordered helical conformation. At DN = 1.0, the enhanced rigidity of the complex hinders the accommodation of the ligands at the interface with polymer chain. This results in appearance of non-bonded side groups in the columns giving rise to a poorly-ordered structure. In contrast to more rigid chains of poly(4-vinylpyridine), the transition from lamellar to columnar mesophase in P2VP occurs at lower DNs, indicating a significant role of the chain flexibility in the formation of ordered structures

Aqueous microgels modified with photosensitive wedge-shaped amphiphilic molecules: synthesis, structure and photochemical behaviour

International audienceAqueous microgels based on poly(N-vinylcaprolactam) with reversible temperature-induced volume transition are promising “smart” materials for various applications. In this work, the microgels are modified via acid–base interaction by wedge-shaped amphiphilic sulfonic acid molecules with alkyl chains of different lengths and an azobenzene group. In contrast to the pristine microgel the modified microgels retain colloidal stability in water and show different responses to the change of temperature and pH. The azobenzene group in the ligand molecules acts as a spectroscopic and kinetic probe sensing the microenvironment inside the microgel particles. Thus, the observed hyperchromicity upon heating suggests the enhancement of hydrophobicity with the increase of temperature. The hydrophobicity of the microgel interior increases with the increase of the modification degree as indicated by the increase of activation energy of the thermal Z/E isomerization of the azobenzene group

Control of Self-Assembly of Amphiphilic Wedge-Shaped Mesogens Using a Combination of Magnetic Field and Temperature Treatment

The report elucidates for the first time a significant effect of a strong magnetic field combined with thermal treatment on the texture of thin liquid-crystalline films in a smectic state. The metastable texture generated in the magnetic field was arrested via the crystallization of mesogens while they cooled to room temperature. The effect was demonstrated on a series of wedge-shaped amphiphilic mesogens based on 1,2,3-tris-(dodecyloxy)benzene (TDOB): asymmetric 2,3,4-tris-(dodecyloxy)benzenesulfonic acid (TDOBSH) and its sodium (TDOBSNa) and pyridine (TDOBSPyr) salts. The thermotropic properties and the structure of the liquid crystal phases of the synthesized compounds were studied using differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. It was shown that, depending on the type of counterion, the synthesized mesogens formed different supramolecular structures. The largest effect of the intense magnetic field was observed for the pyridine salt for which an ordered primitive cubic phase texture was generated upon the normal application of the magnetic field with respect to the film. In contrast, for the corresponding acid, an improvement of the gyroid cubic phase orientation was detected with the magnetic field oriented along the film. A highly ordered columnar phase of the sodium salt was affected only minimally by the magnetic field

Control of Self-Assembly of Amphiphilic Wedge-Shaped Mesogens Using a Combination of Magnetic Field and Temperature Treatment

The report elucidates for the first time a significant effect of a strong magnetic field combined with thermal treatment on the texture of thin liquid-crystalline films in a smectic state. The metastable texture generated in the magnetic field was arrested via the crystallization of mesogens while they cooled to room temperature. The effect was demonstrated on a series of wedge-shaped amphiphilic mesogens based on 1,2,3-tris-(dodecyloxy)benzene (TDOB): asymmetric 2,3,4-tris-(dodecyloxy)benzenesulfonic acid (TDOBSH) and its sodium (TDOBSNa) and pyridine (TDOBSPyr) salts. The thermotropic properties and the structure of the liquid crystal phases of the synthesized compounds were studied using differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. It was shown that, depending on the type of counterion, the synthesized mesogens formed different supramolecular structures. The largest effect of the intense magnetic field was observed for the pyridine salt for which an ordered primitive cubic phase texture was generated upon the normal application of the magnetic field with respect to the film. In contrast, for the corresponding acid, an improvement of the gyroid cubic phase orientation was detected with the magnetic field oriented along the film. A highly ordered columnar phase of the sodium salt was affected only minimally by the magnetic field

Tuning the properties of electrospun polylactide mats by ethanol treatment

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