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Supramolecular complexation between photoresponsive azobenzene chromophores andaphotopassive polymer host offers synthetic and design advantages compared with conventional covalent azo-containing polymers. In this context, it is important to understand the impact of the strength of the supramolecular interaction on the optical response. Herein, we study the effect of hydrogen-bonding strength between a photopassive polymer host [poly(4-vinylpyridine), or P4VP] and three azobenzene analogues capable of forming weaker (hydroxyl), stronger (carboxylic acid), or no H-bonding with P4VP. The hydroxyl-functionalized azo forms complete H-bonding complexation up to equimolar ratio with VP, whereas the COOH-functionalized azo reaches only up to 30% H-bond complexation due to competing acid dimerization that leads to partial phase separation and azo crystallization. We show that the stronger azo-polymer H-bonding nevertheless provides higher photoin-duced orientation and better performance during optical surface patterning, in terms of grating depth and diffraction efficiency, when phase separation is either avoided altogether or is limited by using relatively low azo contents. These results demonstrate the importance of the H-bonding strength on the photoresponse of azopolymer complexes, as well as the need to consider the interplay between different intermolecular interactions that can affect complexation. Key words: supramolecular complexes, azo-containing materials, photo-orientation, surface relief gratings. La complexation supramoleculaire entre des chromophores azobenzeniques photosensibles et un hote polymerique photopassif offre des avantages sur le plan de la synthese et de la conception par rapport aux polymeres azoiques covalents classiques. Dans ce contexte, il importe de comprendre les effets de la force des interactions supramoleculaires sur la reponse optique. Dans le cadre des presents travaux, nous avons etudie l'effet de la force des liaisons hydrogene entre un hote polymerique photopassif--la poly(4-vinylpyridine), ou P4VP - et trois analogues azobenzeniques capables de former des liaisons hydrogene faibles (hydroxyle) ou fortes (acide carboxylique) avec la P4VP, ou de ne former aucune liaison hydrogene. Les composes azoiques hydroxyles se complexent entierement par liaisons hydrogene avec la VP, la complexation atteignant un rapport equimolaire, tandis que les composes azoiques carboxyles n'atteignent qu'un taux de complexation par liaisons hy-drogene de 30%. Ce dernier resultat est attribuable a la dimerisation de l'acide, qui entre en competition, entrainant une separation de phases partielle et la cristallisation du compose azoique. Nous demontrons que les liaisons hydrogene plus fortes avec le polymere azoique permettent neanmoins une orientation photo-induite plus importante et une meilleure performance durant le modelage optique de la surface, notamment en ce qui concerne la profondeur du reseau et l'efficacite de diffraction, lorsque la separation de phases est evitee completement ou limitee par l'utilisation de quantites relativement faibles de compose azoique. Ces resultats demontrent l'influence de la force des liaisons hydrogene sur la photosensibilite des complexes de polymeres azoiques de meme que la necessite de prendre en compte l'interrelation entre les differentes interactions inter-moleculaires qui peuvent intervenir dans la complexation. [Traduit par la Redaction] Mots-cles : complexes supramoleculaires, composes azoiques, photo-orientation, reseaux de surface., Introduction Supramolecular chemistry, basedon specific noncovalent interactions between complementary molecules, is an excellent tool for building libraries of functional materials, because one structural material element at a time can be [...]

Electrospun fibers of amorphous or low-crystallinity polymers typically exhibit a low molecular orientation that can hamper their properties and application. A key stage of the electrospinning process that could be harnessed to mitigate the loss of orientation is jet rigidification, which relates closely to the solvent evaporation rate. Here, we establish quantitative Raman methods to assess the molecular orientation and crystallinity of weakly crystalline poly(2,6-dimethyl-1,4-phenylene oxide) fibers with varying diameters. Our findings demonstrate that solvent volatility can be leveraged to modulate the orientation and crystallinity through its impact on the effective glass transition temperature (T g,eff) of the polymer jet during the electrospinning process. Specifically, a highly volatile solvent yields a higher and more sustained orientation (median ⟨ P 2⟩ of 0.53 for diameters < 1.0 µm) because its fast evaporation rapidly increases T g,eff above room temperature. This vitrification early along the jet path promotes the formation of an oriented amorphous phase and a moderate fraction of strain-induced crystals. Our data reveals that a high T g is a crucial parameter for reaching high orientation in amorphous or low-crystallinity polymer systems. Graphical Abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

A novel method is presented that is capable of collecting time-resolved vibrational spectroscopic information with sub-100-[micro]s temporal resolution. Unlike previous step scan FT-IR approaches, the phenomena under study do not necessarily need to be repeatable. The methodology described herein is based on the planar array infrared (PA-IR) technique, which utilizes a spectrograph for wavelength dispersion and a mid-infrared focal plane array (FPA) detector for simultaneous detection of multiple wavelengths. Unlike previous PA-IR approaches, a rolling mode FPA is employed. This unique data readout mode, where data are read out of the array two rows at a time, is exploited to generate increased temporal resolution. The capabilities of this technique are demonstrated using the example of the electric field-induced Freedericksz transition of a nematic liquid crystal. It is shown that the orientational dynamics of a single transition can be tracked over a spectral range of 154 [cm.sup.-1] with a temporal resolution of 99.17 [micro]s while requiring a total experimental time of less than 1 s.