Search

Tailoring the properties of electrospun fibers requires a detailed understanding and control of their microstructure. We investigate the structure/property relationships in fabrics of randomly aligned fibers of polylactide, a prevalent biopolymer, either as-spun or after annealing and solvent-induced crystallization. In-depth characterization by field-emission scanning electron microscope (FESEM), wide-angle X-ray diffraction (WAXD), attenuated total reflection Fourier transform infrared (ATR-FTIR), and modulated temperature differential scanning calorimetry (MT-DSC) reveals that the as-spun fibers comprise crystalline and mesomorphic phases, as well as oriented but mobile amorphous chain segments. These chains are mostly responsible for the low-temperature cold crystallization and for the recovery endotherm around the glass transition, while the mesophase transforms into crystals with nearly zero enthalpy. Such behaviors are attributed to high molecular orientation, which is further evidenced by unveiling a fibrillar superstructure in nanofibers. The thermodynamics and structural evolution under different conditions are described from an energy landscape perspective. Finally, we propose a micromechanism, based on a modified supramolecular model, which helps to elucidate the fibers’ molecular dynamics.

Eumelanin, a macromolecular biopigment, is an attractive candidate for sustainable (green) organic electronics. Establishing structure–property relationships in eumelanin films is an essential step to exploit its technological potential. We report on the evolution from the molecular state to film after spin coating on silicon dioxide solutions of (5,6)-dihydroxyindole (DHI) and (5,6)-dihydroxyindole-2-carboxylic acid (DHICA) eumelanin building blocks (monomers). The evolution of the spin-coated films was studied under various environmental conditions, such as ambient vs an ammonia atmosphere, which catalyzes polymerization. Atomic force microscopy images reveal dramatic morphological changes as a function of the environmental conditions. Infrared and UV–vis spectroscopies indicate that these changes are due to a combination of physical (self-assembly) and chemical (polymerization) processes. Preliminary electrical measurements on films were also carried out.

Elucidating the influence of the monolayer interface versus bulk on the macroscopic properties (e.g., surface hydrophobicity, charge transport, and electron transfer) of organic self-assembled monolayers (SAMs) chemically anchored to metal surfaces is a challenge. This article reports the characterization of prototypical SAMs of n-alkanethiolates on gold (CH3(CH2)nSAu, n = 6–19) at the macroscopic scale by electrochemical impedance spectroscopy and contact angle goniometry, and at the molecular level, by infrared reflection absorption spectroscopy. The SAM capacitance, dielectric constant, and surface hydrophobicity exhibit dependencies on both the length (n) and parity (nodd or neven) of the polymethylene chain. The peak positions of the CH2 stretching modes indicate a progressive increase in the chain conformational order with increasing n between n = 6 and 16. SAMs of nodd have a greater degree of structural gauche defects than SAMs of neven. The peak intensities and positions of the CH3 stretching modes are chain length independent but show an odd–even alternation of the spatial orientation of the terminal CH3. The correlations between the different data trends establish that the chain length dependencies of the dielectric constant and surface hydrophobicity originate from changes in the polymethylene chain conformation (bulk), while the odd–even variation arises primarily from a difference in the chemical composition of the interface related to the terminal group orientation. These findings provide new physical insights into the structure–property relation of SAMs for the design of ultrathin film dielectrics as well as the understanding of stereostructural effects on the electrical characteristics of tunnel junctions.

We demonstrate a unique combination of simultaneous top-down and bottom-up control of the morphology of block copolymer films by application of in situ optical irradiation during dip-coating. A light-addressable and block-selective small molecule, 4-butyl-4′-hydroxyazobenzene (BHAB), is introduced into a diblock copolymer of polystyrene and poly(4-vinylpyridine) (PS-P4VP) of 28.4 wt % P4VP via supramolecular chemistry, notably by hydrogen bonding to P4VP. We show that the spherical morphology of thin films dip-coated from a THF solution at slow withdrawal rates in the dark convert to cylindrical morphology when dip-coated under illumination. This is attributed to volume expansion of the P4VP/BHAB phase due to trans–cis photoisomerization combined with a light-induced increase in BHAB uptake in the film. The demonstrated photocontrol highlights the potential of dip-coating as a scalable film preparation method that can be easily coupled with external stimuli to direct nanostructured self-assembly in the films as solvent evaporates.

Funding Information: For financial support, Jukka Niskanen acknowledges the Department of Chemistry of the University of Montreal (Canada), and Jaana Vapaavuori is grateful for funding from Banting Postdoctoral Fellowship (Canada). Christian Pellerin acknowledges funding from the Natural Sciences and Engineering Research Council of Canada (NSERC #RGPIN‐2015‐04014). Dmitri Golberg is grateful to the Australian Research Council (ARC) for granting a Laureate Fellowship FL160100089 and Discovery project DP170100131. Publisher Copyright: © 2021 Wiley Periodicals LLC. Understanding interfacial interactions in polymer systems is crucial for their applicability for instance in adhesives and coatings. Enclosing polymers in a cylindrical volume provides a system for studying interactions dictated by a continuous interfacial layer and a bulk-like volume in the middle of the cylinders. Here, we describe a simple method for enclosing polymers into boron nitride nanotubes (BNNTs) and establishing the effect of the interfacial interactions on the glass transition temperature (Tg) of the polymers by infrared spectroscopy. The volume of the inner channel is large in comparison to the volume of the loaded polymer coils, allowing the polymer to expand along the inner channel, resulting in the effect of interfacial interactions on polymer dynamics dominating over confinement effects. As examples, we loaded poly(4-vinyl pyridine), poly(methyl methacrylate), poly(vinyl pyrrolidone), and poly(disperse red 1 acrylate) in BNNTs. The strongest interaction between the studied polymer and BNNTswas observed for poly(4-vinyl pyridine), which also caused a significant increase of Tg. In addition to characterizing the effect of interfacial interactions on the thermal transitions of the polymers, this method, which is generalizable to most soluble polymer materials, can be used for studying photoinduced transitions in photoactive polymers thanks to the transparency of the BNNTs at visible wavelengths.

*These authors contributed equally.Electrospun fibers often exhibit enhanced properties at reduced diameters, a characteristic now widely attributed to a high molecular orientation of the polymer chains along the fiber axis. A parameter that can affect the molecular organization is the type of collector onto which fibers are electrospun. In this work, we use polarized confocal Raman spectromicroscopy to determine the incidence of the three most common types of collectors on the molecular orientation and structure in individual fibers of a broad range of diameters. Poly(ethylene terephthalate) is used as a model system for fibers of weakly crystalline polymers. A clear correlation emerges between the choice of collector, the induced molecular orientation, the fraction of trans conformers, and the degree of crystallinity within fibers. Quantitative structural information gathered by Raman contributes to a general description of the mechanism of action of the collectors based on the additional strain they exert on the forming fibers., Graphical Abstract

With the idea of improving the mechanical properties of acrylonitrile–butadiene rubber (NBR) for potential industrial application, hybrid nanofillers prepared by hybridizing graphene oxide (GO) wit...

The rate of photomechanical formation of surface relief gratings (SRG) in thin films of azobenzene materials depends on their glass transition temperature (Tg), with an optimal Tg around 50–60 °C yielding the fastest SRG growth. Herein, the SRG growth of five analogous Disperse Red 1 molecular glasses with Tg values ranging from 9 to 71 °C was studied with two different laser wavelengths (488 and 532 nm). It was found that the optimal Tg for SRG growth increases with laser irradiance, from approximately 50 °C at 100 mW cm−2 to over 70 °C at 300 mW cm−2. Furthermore, the azobenzene glass with a sub-ambient Tg of 9 °C can inscribe self-erasable gratings that collapse spontaneously when irradiation is stopped in a repeatable fashion, thereby paving the way for light-controlled optical devices.

Gel polymer electrolytes (GPEs) based on polyacrylonitrile elastomer (HNBR) are investigated for lithium-ion batteries application. This study examines the acrylonitrile content, as well as the sol...

Dip-coating allows nanostructured block copolymer (BCP) thin film fabrication in a fast and facile one-step process. It can also be coupled with external controls, such as illumination. Herein, we expose several design principles that enable photocontrol of the nanostructured surface pattern and thickness of supramolecular BCP thin films. This is done using a polystyrene–poly(4-vinylpyridine) (PS-P4VP) BCP and two hydroxy-functionalized small-molecule (SM) azo derivatives that have different photochemical characteristics and that hydrogen bond to the P4VP block. We show how the film preparation concept provides tunability through the chemical structure of the photoactive SM, the relative amount of SM in the dip-coating solution, and the choice of solvent. It was found that the film thickness and SM uptake in the films are increased by illumination when THF is used but are unchanged when toluene is used as solvent, which is attributed to an optical heating effect observable with volatile solvents. The photocontrol of surface patterns is a result of photoinduced changes in the effective volume fraction of the P4VP+SM phase, which is increased by a greater volume of cis isomers, by higher SM uptake (using THF), and by more trans–cis–trans cycling for systems with shorter cis lifetime. The extent of photoinduced change can also be increased by higher molecular mobility due to more flexible SMs, lower BCP molecular weight, and nonmicellar or softer micellar solutions.

As part of continuing efforts to deepen the understanding of photo-induced mass transport in azo-containing polymers, we compared the diffraction efficiency (DE) during surface-relief grating (SRG) inscription, photo-induced molecular orientation (), and thermal stability in two sets of supramolecular azopolymer complexes, namely, hydrogen-bonded (H-bonded) and ionically bonded (i-bonded) complexes, both as a function of the polymer degree of polymerization (DP). To that end, poly(4-vinylpyridine) (P4VP) polymers with DPs of 41, 480, and 1900 were H-bonded at an equimolar ratio with 4-hydroxy-4′-dimethylaminoazobenzene (azoOH), and the fully quaternized derivatives of the three P4VPs (P4VPMe) were i-bonded via ion exchange to sodium 4-[(4-dimethylamino)-phenylazo]benzene sulfonate (azoSO3), also known as methyl orange, where the OH functionality of azoOH is replaced by a sulfonate group. The i-bonded complexes show much better DE performances and levels than those of H-bonded complexes, which we relate to the liquid crystal structure of the former complexes. Fitting the curves by a biexponential equation leads to two parameters associated with a fast trans–cis or angular hole burning (AHB) process and a slow angular redistribution (AR) process of the azo, respectively. It is found that AHB is predominant in the H-bonded complexes, whereas the AR contribution is much greater in the i-bonded complexes, assuring their superior SRG efficiency that is enabled by the anisotropic free volume created mainly by the AR process. In each set of complexes, the SRG efficiency is much better for the lowest DP complex, while the AR contribution is constant (and low) for the H-bonded complexes and increases roughly linearly with the decrease in DP for the i-bonded complexes. The latter difference might be related to the presence of entanglements in the complexes with DPs 480 and 1900, which slow down the macroscopic movement during SRG inscription but not the molecular-scale movement in photo-orientation.

Electrospun nanofibers (NFs) often demonstrate an exponential increase in mechanical and other properties at reduced diameters. Molecular orientation emerges as a key parameter for the performance of amorphous and low crystallinity polymers, but single-fiber structural investigations are still lacking for highly crystalline polymers. Herein, polarized confocal Raman spectroscopy reveals that fibers of highly crystalline poly(ethylene oxide) (PEO) maintain a high orientation over a broad range of diameters, in strong contrast with the usual exponential trend. This observation stands for five electrospinning solvents of widely different properties. By comparison, poly(oxymethylene) (POM) NFs also show a high orientation at low diameters, but it decreases substantially for diameters larger than ∼1400 nm, a result attributed to the lower crystallinity of POM compared to that of PEO. The results show that the exponential orientation dependence on fiber diameter is not universal and stress the importance of polymer crystallinity on the structure and properties of electrospun nanofibers. This work guides the preparation of fibers with optimal orientation-dependent properties and shows that high crystallinity can afford more robust materials whose performance is less affected by variations in experimental conditions, a valuable feature for most applications.

A challenge in glass engineering is the design of molecular glasses combining a high glass kinetic stability (GS) of the amorphous phase with a low (sub-ambient) glass transition temperature (Tg). Triazine derivatives with arylamino substituents readily form glassy phases that can show outstanding resistance to crystallization. In the present study, a series of 12 analogous compounds incorporating phenylamino and cyclohexylamino groups was synthesized, and their thermal properties and intermolecular interactions were studied. All compounds possess an excellent glass-forming ability, a low Tg ranging from 32 °C to as low as −19 °C, and a high GS. While the cyclohexyl derivatives show higher Tg, the phenyl derivatives possess a higher GS with some compounds remaining completely amorphous for over three years despite their sub-ambient Tg. X-ray diffraction, infrared spectroscopy and DFT calculations reveal that the higher volume occupancy and rotational energy barrier of cyclohexyl groups are the main factors responsible for the compounds' higher Tg values but that they also contribute to their higher propensity to crystallize. In counterpart, the planarity of phenyl groups leads to poorer packing and enhances their GS while keeping their Tg well below ambient. The formation of hydrogen bonds or competing interactions provides an additional handle to tune the Tg of the compounds. Taken together, these studies provide guidelines for the design of molecular glasses with readily tunable thermal properties in view of their functionalization.

Hydrogen bonding is a key element of supramolecular chemistry and is often used in crystal engineering to direct crystal packing. In particular, systems where motifs with multiple hydrogen (H) bonds are present, such as the donor–acceptor–donor – acceptor–donor–acceptor (DAD–ADA) synthon, can be used to generate various supramolecular architectures. However, H-bonding can also be used to frustrate crystallization if it impedes an efficient molecular packing, instead resulting in glass formation. Herein, triazine-based molecular glass-formers, which can form multiple hydrogen bonds and show outstanding resistance to crystallization, are strategically used to hinder the crystallization of barbiturate derivatives, even in blends with low molar fractions, depending on the structure of the glass-former. Besides the strong DAD–ADA motifs, the molecules can form several sub-optimal motifs that can serve to hinder the crystallization of the barbiturate component during solvent evaporation or cooling. A triazine derivative with a covalently bound barbituric acid moiety was also synthesized, and did also not show any crystallization, showing that the presence of strong and predictable hydrogen bonding motifs does not necessarily contribute to crystallization. Our results highlight molecular design guidelines to hinder the crystallization of a compound, either by covalent functionalization or by blending with a glass-former capable of establishing similar interactions, thus leading to a variety of motifs for glass engineering.

The black-brown biopigment eumelanin screens the harmful ultraviolet (UV) radiation in the human skin. In industry, the absorption of plastics in the UV range is improved by the inclusion of additives. Our work reports an evaluation of the biopigment eumelanin as a nature-inspired additive for polymers to improve their UV-absorption. Eumelanin, being non-toxic and produced by natural sources, represents an interesting candidate for sustainable plastic additives. We fabricated eumelanin-including films of commercial linear low-density polyethylene (LLDPE), a plastic ubiquitous in packaging applications. The films were obtained by melt-compounding and compression molding. The melanin free acid treatment (MFA) was used to enhance the biopigment dispersion in the films. We observed that amounts of eumelanin as low as 0.8% wt. bring about an increase of the UV absorption up to one order of magnitude in the UVA range. We also assessed the effect of eumelanin on the film stability under prolonged UV irradiation: the biopigment proved to work both as UV-absorption enhancer but also as a photo-prooxidant, as inferred by thermogravimetric analysis (TGA) and infrared (IR) spectroscopy.

To optimize azobenzene-containing materials for applications such as rewritable waveguides and holographic data storage, it is imperative to understand the effect of the azobenzene structure on the photoresponse of the material. Supramolecular materials, in which a complexed photoactive azobenzene controls the motion or other properties of a passive polymer, are uniquely convenient for studying the impact of specific chemical modifications. Here, we use polarization modulation infrared structural absorbance spectroscopy (PM-IRSAS) to hydrogen-bonded supramolecular azobenzene complexes using poly(4-vinylpyridine) (P4VP) as a model polymer. We show that changing the tail group from hydrogen (AH) to cyano (ACN) induces greater angular redistribution of the chromophores and, remarkably, provokes P4VP pyridine ring orientation. Increasing the degree of complexation decreases the saturated orientation of both AH and ACN, whereas for P4VP/ACN it increases the pyridine orientation as well as the orientation stability of both components. These results explain the contrasting photoinduced birefringence behavior previously observed for these complexes and identify azo-azo intermolecular interactions as the main reason. To our knowledge, this is the first molecular-level spectroscopic analysis of the contrasting contributions of azobenzenes to the photo-orientation of supramolecular azopolymer complexes and the first report of the large impact of small molecular changes on the capacity of azo dyes to transfer light-induced orientation to a photopassive polymer.

A star shaped poly(sulfobetaine methacrylate) (PSBMA) and its linear analogs, display upper-critical-solution-temperature (UCST) type behavior in 0.1 M NaCl. The presence of sodium dodecyl sulfate (SDS) or cetyl trimethyl ammonium bromide (CTAB) has a significant effect on the thermal transition of the polymer. The association of the polymer with the surfactants is confirmed by isothermal titration calorimetry (ITC) and infrared (IR) spectroscopy. SDS forms hydrophobic domains along the polymer chains, preventing the polymers from undergoing a thermal phase transition. These domains can be used to capture 1-anilino-8-naphthalenesulfonate (1,8-ANS), pyrene and curcumin, and increase their fluorescence intensity. Curcumin, which is unstable in aqueous solutions, is stabilized against degradation upon solubilization by the PSBMA-SDS complexes.

Electrospun fibers are complex polymeric materials with a typical diameter of a few hundred nanometers that are often frozen in out-of-equilibrium states due to the fast solvent evaporation and high elongational forces during the process. Their molecular orientation, and the parameters affecting it, is a critical (although challenging) parameter to characterize because it allows improving and tuning many properties. In this paper, we characterize molecular orientation of poly(ethylene oxide) (PEO) fibers produced with the three most common collectors by applying our recently developed Raman spectroscopy methodologies to probe individual fibers. Results reveal an extremely high orientation in all PEO fibers and, surprisingly, the absence of any effect of the collector on molecular orientation. This contrasts with reports by several other research groups in the context of studies on bundles of fibers, as well as with our WAXD results on the same fibers. It is concluded that studies on bundles composed of thousands of imperfectly aligned fibers lead to a systematic underestimation of the orientation and to apparent results that prevent us from drawing clear conclusions on the molecular impact of processing parameters when they generate different levels of macroscopic alignment. This work highlights how Raman spectroscopy helps to overcome one of the major challenges in the field, the characterization of individual fibers, to reach a better understanding and control of electrospun fibers properties.

It has recently been established that physical vapor deposition (PVD) can produce organic glasses with enhanced kinetic stability, high density, and anisotropic packing, with the substrate temperature during deposition (Tsubstrate) as the key control parameter. The influence of hydrogen bonding on the formation of PVD glasses has not been fully explored. Herein, we use a high-throughput preparation method to vapor-deposit three triazine derivatives over a wide range of Tsubstrate, from 0.69 to 1.08Tg, where Tg is the glass transition temperature. These model systems are structural analogues containing a functional group with different H-bonding capability at the 2-position of a triazine ring: (1) 2-methylamino-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (NHMe) (H-bond donor), (2) 2-methoxy-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (OMe) (H-bond acceptor), and (3) 2-ethyl-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (Et) (none). Using spectroscopic ellipsometry, we find that the Et and OMe compounds form PVD glasses with relatively high kinetic stability, with the transformation time (scaled by the α-relaxation time) on the order of 103, comparable to other highly stable glasses formed by PVD. In contrast, PVD glasses of NHMe are only slightly more stable than the corresponding liquid-cooled glass. Using IR spectroscopy, we find that both the supercooled liquid and the PVD glasses of the NHMe derivative show a higher average number of bonded NH per molecule than that in the other two compounds. These results suggest that H-bonds hinder the formation of stable glasses, perhaps by limiting the surface mobility. Interestingly, despite this difference in kinetic stability, all three compounds show properties typically observed in highly stable glasses prepared by PVD, including a higher density and anisotropic molecular packing (as characterized by IR and wide-angle X-ray scattering).

Supramolecular complexation between photoresponsive azobenzene chromophores and a photopassive 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 photoinduced 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., La complexation supramoléculaire entre des chromophores azobenzéniques photosensibles et un hôte polymérique photopassif offre des avantages sur le plan de la synthèse et de la conception par rapport aux polymères azoïques covalents classiques. Dans ce contexte, il importe de comprendre les effets de la force des interactions supramoléculaires sur la réponse optique. Dans le cadre des présents travaux, nous avons étudié l’effet de la force des liaisons hydrogène entre un hôte polymérique photopassif — la poly(4-vinylpyridine), ou P4VP – et trois analogues azobenzéniques capables de former des liaisons hydrogène faibles (hydroxyle) ou fortes (acide carboxylique) avec la P4VP, ou de ne former aucune liaison hydrogène. Les composés azoïques hydroxylés se complexent entièrement par liaisons hydrogène avec la VP, la complexation atteignant un rapport équimolaire, tandis que les composés azoïques carboxylés n’atteignent qu’un taux de complexation par liaisons hydrogène de 30%. Ce dernier résultat est attribuable à la dimérisation de l’acide, qui entre en compétition, entraînant une séparation de phases partielle et la cristallisation du composé azoïque. Nous démontrons que les liaisons hydrogène plus fortes avec le polymère azoïque permettent néanmoins 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 réseau et l’efficacité de diffraction, lorsque la séparation de phases est évitée complètement ou limitée par l’utilisation de quantités relativement faibles de composé azoïque. Ces résultats démontrent l’influence de la force des liaisons hydrogène sur la photosensibilité des complexes de polymères azoïques de même que la nécessité de prendre en compte l’interrelation entre les différentes interactions intermoléculaires qui peuvent intervenir dans la complexation.

Knowledge of the thermotropic phase behavior of solid-supported bilayer lipid assemblies is essential to mimick the molecular organization and lateral fluidity of cell membranes. The gel-to-fluid phase transitions in a homologous series of single phospholipid bilayers supported on planar silicon substrates were investigated by temperature-controlled atomic force microscopy and attenuated total reflection infrared spectroscopy to obtain complementary information at the mesoscopic and molecular scales. Symmetric bilayers of dipalmitoylphosphatidylcholine (DPPC) and vertically asymmetric bilayers composed of a leaflet of DPPC and another of acyl-chain-deuterated DPPC (DPPC-d62) were prepared by the Langmuir-Blodgett technique. The selective deuteration of one of the bilayer leaflets enabled the simultaneous monitoring by IR spectroscopy of the acyl chain melting in each leaflet via the spectrally isolated CH2 and CD2 stretching vibrations. Two gel-to-fluid transitions were discerned for both the symmetric and asymmetric bilayers in ultrapure water. The deuterium isotope effect observed in free-standing membranes was maintained for the supported bilayers. IR spectroscopy revealed that the melting of one leaflet promotes the disordering of the acyl chains in the adjacent one. The findings suggest that the two leaflet phase transitions do not evolve in isolation. This work sheds insight into the nature of leaflet-leaflet interactions and the thermodynamic properties of surface-confined phospholipid bilayers.

International audience; Advanced fibers revolutionized structural materials in the second half of the 20th century. However, all high-strength fibers developed to date are brittle. Recently, pioneering simultaneous ultrahigh strength and toughness were discovered in fine (

Introducing photochromic or polymeric dopants into nematic liquid crystals is a well-established method to create stimuli-responsive photonic materials with the ability to "control light with light". Herein, we demonstrate a new material design concept by showing that specific supramolecular interactions between the host liquid crystal and the guest dopants enhance the optical performance of the doped liquid crystals. By varying the type and strength of the dopant-host interaction, the phase-transition temperature, the order parameter of the guest molecules, and the diffraction signal in response to interference irradiation, can be accurately engineered. Our concept points out the potential of supramolecular interactions in liquid-crystal photonics, being valuable for optimizing the design of dye-doped functional liquid-crystalline systems. publishedVersion

Langmuir–Blodgett (LB) films of amphiphilic block copolymers (BCs) form well-defined nanostructures with long-range order useful, for instance, for nanolithography applications. Nanostructures with a 2D circular micelle (“dot”) morphology are known to present a constant pressure plateau in their Langmuir isotherm (surface pressure vs molecular area curve at the air/water interface), indicative of a first-order transition. We have previously shown, with LB films of polystyrene-b-poly(4-vinylpyridine) (PS-P4VP) and its supramolecular complex with 3-n-pentadecylphenol (PDP), that there is an order–order transition of the dots from hexagonal to square at the plateau. However, various literature results indicate that the molecular-level understanding of the transition is poorly understood. Here, using polarized infrared spectroscopy on the PS-P4VP/PDP system, we identify what molecular changes occur at the plateau. The only changes found are an edge-on to isotropic orientation of the pyridine rings and an increase in the level of P4VP hydrogen bonding with PDP; no changes are found in alkyl chain conformation or orientation. On the basis of these results and AFM observations of the film morphologies, we propose a new mechanism involving 2D to 3D folding of the P4VP chains on the water surface at the plateau pressure that connects the molecular changes with the hexagonal-square reorganization of the dot array. We further show how the model can be generalized to dot-forming LB films of pure PS-P4VP and other BC systems and even to BC monolayers obtained by spin-coating from dilute solutions. This study thus lays the foundation for a generalized fundamental understanding of dot-forming LB block copolymer films and enables predicting their behavior in order to precisely control their organization and, ultimately, their properties at different length scales.

The byssus that anchors mussels to solid surfaces is a protein-based material combining strength and toughness as well as a self-healing ability. These exceptional mechanical properties are explained in part by the presence of metal ions forming sacrificial bonds with amino acids. In this study, we show that the properties of hydrogel films prepared from a byssus protein hydrolyzate (BPH) can also be improved following the biomimetic formation of sacrificial bonds. Strengthening and toughening of the materials are both observed when treating films with multivalent ions (Ca2+ or Fe3+) or at the BPH isoelectric point (pI) as a result of the formation of metal–ligand bonds and salt bridges, respectively. These treatments also provide a self-healing behavior to the films during recovery time following a deformation. While pI and Ca2+ treatments have a similar but limited pH-dependent effect, the modulus, strength, and toughness of the films increase largely with Fe3+ concentration and reach much higher values. The affinity of Fe3+ with multiple amino acid ligands, as shown by vibrational spectroscopy, and the more covalent nature of this interaction can explain these observations. Thus, a judicious choice of treatments on polyampholyte protein-based materials enables control of their mechanical performance and self-healing behavior through the strategic exploitation of reversible sacrificial bonds.

Large-area metal/molecule/metal junctions based on self-assembled monolayers (SAMs) of organothiolates are of interest for investigations of charge transport across ultrathin organic films and the fabrication of molecular electronic devices. Several recent reports demonstrate an odd-even dependency in the rate of charge transport through SAMs of the insulating n-alkanethiolates (CH3C n S)1,2 or the redox-active ferrocenylalkanethiolates (FcC n S)3. This parity effect has been attributed to differences in the orientation of the terminal functional group and alkyl chain packing in SAMs consisting of an odd versus even number of methylene repeat units. We have sought experimental evidence for odd-even distinctions in the molecular organization of these SAMs using infrared reflection-adsorption spectroscopy (IRRAS), electrochemistry, and contact angle goniometry. The findings of the investigations will be presented in this talk and the molecular origin of the parity effect of SAM macroscopic properties will be discussed. References: 1. Baghbanzadeh, M.; Simeone, F. C.; Bowers, C. M.; Liao, K.-C.; Thuo, M.; Baghbanzadeh, M.; Miller, M. S.; Carmichael, T. B.; Whitesides, G. M., Odd–Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs. J. Am. Chem. Soc. 2014, 136, 16919- 16925. 2. Chen, J.; Giroux, T. J.; Nguyen, Y.; Kadoma, A. A.; Chang, B. S.; VanVeller, B.; Thuo, M. M., Understanding Interface (Odd–Even) Effects in Charge Tunneling using a Polished EGaIn Electrode. Phys. Chem. Chem. Phys. 2018, 20, 4864-4878. 3. Thompson, D.; Nijhuis, C. A., Even the Odd Numbers Help: Failure Modes of SAM-Based Tunnel Junctions Probed via Odd-Even Effects Revealed in Synchrotrons and Supercomputers. Acc. Chem. Res. 2016, 49, 2061-2069.

In the human body, the black-brown biopigment eumelanin blocks the harmful ultraviolet (UV) radiation. In the plastics industry, additives are often added to polymers to increase their UV-absorption properties. We herein report an assessment of the biopigment eumelanin as a nature-inspired additive for plastics to enhance their UV-absorption. Since eumelanin is produced by natural sources and is non-toxic, it is an interesting candidate in the field of sustainable plastic additives. In this work, eumelanin-including films of commercial ethylene-vinyl acetate copolymer (EVA), a plastic used for packaging applications, were obtained by melt-compounding and compression molding. The biopigment dispersion in the films was improved by means of the Melanin Free Acid treatment (MFA). It was observed that eumelanin amounts as low as 0.8% wt. cause an increase of the UV absorption, up to one order of magnitude in the UVA range. We also evaluated the effect of eumelanin on the thermal and photostability of the films: the biopigment proved to be double-edged, working both as UV-absorption enhancer and photo-prooxidant, as thermogravimetric analysis (TGA) and infrared (IR) spectroscopy revealed.

Lithium-ion batteries (LiBs) are a mature technology which has attracted much attention over the last three decades with the development of portable devices. With the increasing number of LiBs and their use in electric vehicles, there are persistent efforts to enhance their safety by identifying suitable substitutes for liquid non-aqueous electrolytes, which are highly flammable, volatile, and can cause leakage. To this end, gel polymer electrolytes (GPEs) represent a promising alternative. To be suitable in applications and maximize ionic conductivity, polymers must meet specific requirements, the most important ones being a low glass transition temperature (Tg) and a low crystallinity, as ions move faster in amorphous phase. Moreover, these polymers need to be electrochemically stable and provide mechanical resistance as well as flexibility to the GPE. To increase the conductivity, polymers with polar functional groups that can dissolve salts are required. Several polymers, like PEO or PAN have already been studied but one limitation is their high Tg (above ambient temperature) as well as a high crystallinity which make them brittle and limit the ionic conductivity. To circumvent this limitation, we studied an amorphous polymer based on acrylonitrile monomers. This elastomer, HNBR (Hydrogenated Nitrile Butadiene Rubber), was previously studied by our group and was shown to be thermally cross-linkable, leading to a polymer chemically resistant to electrolytes and electrochemically stable over a wide potential range. Hence, we propose to investigate thermally cross-linked HNBRs to gain a better understanding on the effect of interactions between polar nitrile functions and lithium ions and finally use this system as a GPE for Li-ion battery. To do so, a three-component system comprising HNBR:solvent:LiTFSI was studied to pinpoint the correct ratio to provide the GPE with competitive conductivity. Infrared spectroscopy was used to shed light on the interactions between nitriles and lithium ions while PFG-NMR was utilized to obtain spin-lattice relaxation times (T1) and diffusion coefficients of 7Li and 19F for various HNBR-based GPEs. These results were correlated to EIS measurements and among the GPEs tested, those composed of 2M LiTFSI in propylene carbonate and HNBR with an acrylonitrile content of 50% are the most promising. This study highlights the benefits of high acrylonitrile content in the polymer and the use of a solvent with moderate donor number to promote interactions between nitriles and Li+.

Large-area metal/molecule/metal junctions based on self-assembled monolayers (SAMs) of organothiolates are of interest for the investigation of charge transport across ultrathin organic films and the fabrication of molecular electronic devices such as diodes and switches. Several reports demonstrate an odd-even dependency in the rate of charge transport across SAMs of the redox-active ferrocenylalkanethiolates Fc(CH2) n S1, 2 and insulating n-alkanethiolates CH3(CH2) n S3-6. This parity effect is attributed to small changes in the orientation of the terminal functional group (ferrocene or methyl) and in the alkyl chain packing in SAMs consisting of an odd versus even number of methylene repeat units (n odd or n even). These odd-even differences ultimately impact device performance. For instance, junctions comprising gold-supported Fc(CH2) n S SAMs (Figure 1) of n even present lower leakage currents and rectify current, while those of n odd do not.1, 2 We have sought experimental evidence for odd-even distinctions in the molecular organization of these SAMs using electrochemistry,7 infrared reflection-absorption spectroscopy (IRRAS), contact angle goniometry, and surface stress measurements8. The findings of these investigations will be presented in this talk. References: 1. Nerngchamnong, N.; Yuan, L.; Qi, D.-C.; Li, J.; Thompson, D.; Nijhuis, C. A., The Role of van der Waals Forces in the Performance of Molecular Diodes. Nat. Nanotechnol. 2013, 8, 113-118. 2. Yuan, L.; Thompson, D.; Cao, L.; Nerngchangnong, N.; Nijhuis, C. A., One Carbon Matters: The Origin and Reversal of Odd–Even Effects in Molecular Diodes with Self-Assembled Monolayers of Ferrocenyl-Alkanethiolates. J. Phys. Chem. C 2015, 119, 17910-17919. 3. Baghbanzadeh, M.; Simeone, F. C.; Bowers, C. M.; Liao, K.-C.; Thuo, M.; Baghbanzadeh, M.; Miller, M. S.; Carmichael, T. B.; Whitesides, G. M., Odd–Even Effects in Charge Transport across n-Alkanethiolate-Based SAMs. J. Am. Chem. Soc. 2014, 136, 16919-16925. 4. Thuo, M. M.; Reus, W. F.; Nijhuis, C. A.; Barber, J. R.; Kim, C.; Schulz, M. D.; Whitesides, G. M., Odd−Even Effects in Charge Transport across Self-Assembled Monolayers. J. Am. Chem. Soc. 2011, 133, 2962-2975. 5. Chen, J.; Giroux, T. J.; Nguyen, Y.; Kadoma, A. A.; Chang, B. S.; VanVeller, B.; Thuo, M. M., Understanding Interface (Odd–Even) Effects in Charge Tunneling using a Polished EGaIn Electrode. Phys. Chem. Chem. Phys. 2018, 20, 4864-4878. 6. Jiang, L.; Sangeeth, C. S. S.; Nijhuis, C. A., The Origin of the Odd–Even Effect in the Tunneling Rates across EGaIn Junctions with Self-Assembled Monolayers (SAMs) of n-Alkanethiolates. J. Am. Chem. Soc. 2015, 137, 10659-10667. 7. Feng, Y.; Dionne, E. R.; Toader, V.; Beaudoin, G.; Badia, A., Odd–Even Effects in Electroactive Self-Assembled Monolayers Investigated by Electrochemical Surface Plasmon Resonance and Impedance Spectroscopy. J. Phys. Chem. C 2017, 121, 24626-24640. 8. Dionne, E. R.; Dip, C.; Toader, V.; Badia, A., Micromechanical Redox Actuation by Self-Assembled Monolayers of Ferrocenylalkanethiolates: Evens Push More Than Odds. J. Am. Chem. Soc. 2018, 140, 10063-10066. Figure 1

Recent mechanical studies of ultrafine electrospun polymer nanofibers showed they can simultaneously possess high strength and toughness attributed to high degree of chain alignment coupled with low crystallinity. Quantitative analysis of macromolecular alignment in nanofibers is needed for better understanding of processing/structure/properties relationships and optimization. However, quantification of structural features in nanofibers with ultrafine diameters and low variable crystallinity is highly challenging. Here, we show that application of standard orientation analysis protocols developed for polarized Raman microscopy of bulk polymers and films can lead to severe errors in subwavelength diameter samples. A modified polarized Raman method is proposed and implemented for study of size-dependent orientation in individual nanofibers as small as 140 nm. Macromolecular alignment improved significantly with the reduction of nanofiber diameter, correlating with nanofiber modulus increase. Applicability of the proposed method for quantitative comparative studies of nanofiber systems fabricated from solutions with different solvents is demonstrated.

Mussels’ anchoring threads, named byssus, are collagen-rich fibers with outstanding mechanical properties. Our previous work has shown the possibility of producing a byssus protein hydrolyzate with good film-forming ability, providing a promising new avenue for the preparation of biomaterials. Materials prepared from regenerated fibrous proteins often need additional treatments to reach the performance required for targeted applications. Here, we studied the effect of covalent crosslinking, using a carbodiimide or glutaraldehyde, on the mechanical properties and enzymatic resistance of byssus-based materials. The results show that the mechanical properties of the films can be tuned, and that a higher crosslinking degree leads to increases in modulus and strength accompanied by a loss of extensibility. Structural analysis performed by infrared spectroscopy revealed that crosslinking induces an unexpected transition from aggregated strands to hydrated collagen/PPII-related helical structures. The materials were nevertheless more resistant to collagenase degradation as a result of higher crosslinking density. This new set of materials prepared in aqueous environment could find a niche in tissue engineering.

The electrospinning of continuous fibers normally requires the presence of a network of topological entanglements in solution, limiting the spinnability of low molecular weight polymers. Here, we show that a supramolecular approach can improve, and even render possible, the electrospinning of low molecular weight polymers, illustrated here with poly(4-vinylpyridine) (P4VP), by creating effective (i.e., physical) cross-links via hydrogen bonding or coordination interactions in solution using small molecules. The addition to P4VP solutions in dimethylformamide of 4,4′-biphenol (BiOH), which hydrogen bonds to P4VP, and nitromethane, a poor solvent for P4VP that increases BiOH hydrogen bonding to P4VP, decreases the concentration needed to prepare fibers of 50 kg/mol P4VP by a factor of 2 and enables the formation of unbeaded fibers. Hydrogen bonding in solution is quantified by infrared spectroscopy, and the impact of the supramolecular interactions on the P4VP concentration needed to form a physical network...

Recent literature has shown that the thickness of dip-coated films has a V-shaped dependence on dip-coating rate when very slow rates are included. For supramolecular block copolymer films, small molecule (SM) uptake and film morphology are also rate-dependent, as shown previously for a poly(styrene-b-4-vinylpyridine) (PS–P4VP) block copolymer in THF solutions containing naphthol (NOH) and naphthoic acid (NCOOH). Here, these investigations are extended to p-dioxane, toluene, and CHCl3 solutions. The V-shaped thickness dependence is validated for each solvent, but with the V minimum displaced to lower dip-coating rates and thicknesses for the solvents with lower vapor pressures (p-dioxane, toluene), thereby decreasing the dip-coating rate range of the “capillarity regime” (slow side of the V) and consequently extending that of the “draining regime” (fast side of the V). The SM/VP uptake ratio varies with the nature of the solvent, particularly in the capillarity regime, where it is higher for solvents that...

The fabrication of electrospun fibers generally requires relatively concentrated solutions to have sufficient chain entanglements acting as physical crosslinks during the electrospinning process. We propose a supramolecular approach to diminish the necessary concentration. To this end, we investigated the use of a small hydrogen-bond effective crosslinker, 4,4′-biphenol (BiOH), on the electrospinning behavior of poly(4-vinyl pyridine) (P4VP) in N,N-dimethylformamide (DMF) and in a mixture of DMF and nitromethane (CH3NO2). Since solution rheology plays a crucial role in the electrospinning process, various solution properties were characterized. Coil dimensions showed expansion with addition of BiOH and contraction with addition of CH3NO2 (a poor solvent). Hydrogen-bond crosslinking in solutions of P4VP/BiOH (equimolar pyridine:hydroxyl) was quantified by attenuated total reflection (ATR) infrared spectroscopy, and was found to increase with increasing P4VP concentration, especially in the mixed solvent. Hydrogen-bond crosslinking and the effect of the poor solvent thus enhance the formation of an effectively crosslinked network. This leads to the earlier onset of the apparent semidilute entangled regime and hence to a lower critical concentration for fiber formation, which decreases by a factor of two. Furthermore, the addition of BiOH leads to the appearance of a clear concentrated regime that enables preparing uniform fibers. Based on this supramolecular strategy for increasing the effective crosslinking network, it is possible to prepare long aligned electrospun fibers without the need for using highly viscous solutions.

Exciting new applications, from large-area nanopatterning and templating to soft light-powered robotics, are emerging from the fundamental research on light-triggered changes in macromolecular systems upon photoisomeriza-tion of azobenzene-based molecular photoswitches. The understanding of how the initial molecular-scale photoisomerization of azobenzene, a complex photochemical event in itself, is translated into the response of macromol-ecules and even into macroscopic-scale motion of illuminated azomaterials is an enormous task. The focus here is on how this knowledge has advanced by applying different vibrational spectroscopy techniques that provide rich molecular insight into the photoresponse of chemically specific molecular moieties. In particular, infrared and Raman spectroscopy studies are high-lighted, in the context of phototriggered perturbation of self-assembled structures and photoinduced linear and circular anisotropy, as well as photo-induced surface patterning, with the objective of offering a perspective on how vibrational spectroscopy can help in answering an array of essential yet unsettled questions.

Electrospun fibers show a rich and complex variety of diameter-dependent properties. Chain orientation, confinement, and partial disentanglement are the three main factors that have been proposed to explain these phenomena. While molecular orientation is currently the subject of intensive study, the others are more challenging to probe experimentally. Here, we provide support for partial disentanglement in continuous polystyrene electrospun fibers on the basis of infrared spectroscopy measurements. We show that the fiber’s capability to remain partially disentangled, and ours to detect it, is highly dependent on the initial polymer concentration and on the time the fibers are allowed to accumulate on the collector. A model, based on the core–shell morphology observed for the fibers, is proposed to explain the experimental observations.

Offshore and open sea suspension-culture of mussels is largely in development but, in this particular environment, sleeved mussels are submitted to high-energy oceanographic conditions which could increase fall-offs. In this study, we compared the performance of open sea mussel culture to that of culture in a lagoon environment. Byssus attachment strength, condition index, mechanical properties of individual byssal threads, metal content of the filaments for mussels from both the open sea and the semi-closed lagoon sites were monitored as well as the environmental characteristics of these sites. The spawning event occurred approximately one month earlier for mussels in the open sea than in the lagoon, probably due to a difference in temperature and food availability. The attachment strength of the mussels was weaker in the open sea, even if individual threads were bigger and stronger than in the lagoon. This lower attachment strength seems related to a lower production of byssal threads.

To understand the characteristics of electrospun fibers of poly(4-vinyl pyridine) (P4VP) that are potentially crosslinked by hydrogen-bonding when blended with small molecules like 4,4′-biphenol (BiOH), it is necessary to determine the proportion of hydrogen-bonded pyridine rings (fb) and to contrast it with FOH, the mole percent of OH groups available for interacting with the pyridine rings. While this can be done by Fourier transform infrared spectroscopy (FTIR), two practical difficulties must be overcome. First, the correct intensities of the overlapped bands of free and hydrogen-bonded pyridine must be obtained, which is possible using the second derivative spectra. Second, the band absorption coefficient ratio (a) of the pair of bands must be known. In the P4VP/BiOH system, only the pair of free and hydrogen-bonded pyridine ring bands at 993 and 1007 cm−1 can be used for quantitative analysis. We determined, by analysis of liquid blends of BiOH as well as phenol with a model compound, 4-ethylpyridine (EtPy), using the attenuated total reflection mode (ATR), that a = 0.40. This led to values of fb = FOH, indicative of full complexation of the OH groups to pyridine, in the EtPy/BiOH liquid blends up to the BiOH solubility limit in EtPy (FOH = 60%) and in the EtPy/phenol blends up to FOH = 100%. In the electrospun P4VP/BiOH fibers prepared from solutions with FOH up to about 120%, fb averages 0.76FOH, and full complexation of the pyridine groups is achieved only at about FOH = 160%. In both P4VP/BiOH and EtPy/BiOH, the complexation occurs between one pyridine ring and one hydroxyl group. This work thus shows a new method to quantify the relative number of hydrogen-bonded pyridine rings in P4VP; it is expected to be applicable to other polymer-small molecule and polymer-polymer blends having suitable liquid models.

Summary Electrospinning was applied to DMF solution mixtures of poly(methyl methacrylate) (PMMA) and MO/PVP, which is an azo-containing liquid crystalline complex between methyl orange (MO) and methylated poly(4-vinyl pyridine) (PVP), to obtain composite light-responsive fibers. The average diameter of the fibers, which ranged from 700 nm to 1.5 µm, increases with PMMA content. Differential scanning calorimetry, X-ray diffraction and transmission electron microscopy show that they are microphase separated in the form of interspersed nanostrips of PMMA-rich and MO/PVP(-rich) phases. The MO/PVP(-rich) phase is liquid crystalline (smectic A) as in the bulk, but with no orientation relative to the fiber axis. The birefringence of the fibers observed by polarized optical microscopy is attributed, at least in part, to form birefringence. This study is promising for the preparation of light-responsive fibers based on easy-to-prepare polymer complexes.

Electrospinning is the most versatile and popular technique for preparing nanofibers from a very broad range of polymer systems. In spite of more than 20 years of studies, our understanding of the relationships between the microstructure and the properties of these fibers, and how they are influenced by the electrospinning conditions, remains fragmentary. This is especially true for molecular orientation—a critical parameter that is often invoked to explain the properties of fibers but that is challenging to quantify properly. Recently, the emergence of characterization techniques enabling studies at the single fiber level, including their orientation, has propelled the field in new directions and provided a wealth of new knowledge. In this Perspective, we review and discuss our current understanding of the structure and properties of electrospun nanofibers with a particular emphasis on their molecular orientation. We first describe how studies at the mat level have provided crucial knowledge about the im...

The blue mussels Mytilus edulis are widely cultured in the coastal regions of Canada. However, their production on sleeves attached to long lines in the water column suffers from fall-offs due to byssus weakening, especially during the spawning period. Thus, we tested in laboratory the hypothesis that the spawning event changes the chemical and biochemical composition of byssal threads, resulting in a significant modification of their mechanical properties. Metal composition of byssus is interesting, as the proteins are cross-linked by complexation with metals influencing the breaking force. Our results show that the filaments' diameter and breaking force significantly decreased after spawning, as compared to unspawned individuals. However, no differences in the stress-at-break and strain-at-break were observed between the two experimental groups. Analysis of the lipid composition of the fibers' distal region indicates a very low concentration of total lipids, i.e. M. edulis in laboratory conditions was mainly due to a reduction of the fiber diameter, and cannot be related to changes in lipids, amino acid or metal composition.

The physical properties of polymers are strongly affected by their molecular orientation. In this paper, we demonstrate for the first time a new and improved Raman spectroscopy method to characterize this key parameter. In recent years, Raman spectroscopy has emerged as an indispensable tool for this purpose, but its widespread use is still largely restricted by the experimental complexity and the limitations imposed by the standard quantification procedure, referred in this article as the depol constant (DC) method. We have very recently proposed and established theoretically a simplified quantification approach that is based on the most probable orientation distribution (MPD method). Herein, we demonstrate its experimental validity and its wide applicability by studying a series of samples from three highly dissimilar polymers (HDPE, PET, and PS), and covering the full possible orientation range. We show that the new MPD method overcomes the experimental and theoretical difficulties faced with the curre...

Polarized Raman spectroscopy is widely used to quantify the level of molecular orientation of various types of materials. By using a simplified procedure we call the depol (depolarization) constant (DC) method, since it assumes that the depolarization ratio is a constant. However, our ability to quantify orientation by using the DC method is often limited by the need for a completely isotropic sample showing the same chemical and phase composition as the oriented sample of interest to obtain information on the depolarization ratio. In this paper, we propose a new method for orientation quantification, the most probable distribution (MPD) method, based on the hypothesis that the population distribution is the most probable one. In contrast to the conventional DC procedure, this new method does not require knowledge of the depolarization ratio and eliminates the assumption that it does not evolve on orientation. Simulations show the wide applicability of the MPD method for large sections of the 〈P2〉 〈P4〉 diagram, especially for coordinates that are most likely to be observed in experimental conditions. They also highlight the significant inaccuracies produced by the conventional DC method due to depolarization ratio errors.

WOS: 000397614200009, PubMed ID: 28153979, Several bivalve species produce byssus threads to provide attachment to substrates, with mechanical properties highly variable among species. Here, we examined the distal section of byssal threads produced by a range of bivalve species (Mytilus edulis, Mytilus trossulus, Mytilus galloprovincialis, Mytilus californianus, Pinna nobilis, Perna perna, Xenostrobus securis, Brachidontes solisianus and Isognomon bicolor) collected from different nearshore environments. Morphological and mechanical properties were measured, and biochemical analyses were performed. Multivariate redundancy analyses on mechanical properties revealed that byssal threads of M. californianus, M. galloprovincialis and P. nobilis have very distinct mechanical behaviours compared with the remaining species. Extensibility, strength and force were the main variables separating these species groups, which were highest for M. californianus and lowest for P. nobilis. Furthermore, the analysis of the amino acid composition revealed that I. bicolor and P. nobilis threads are significantly different from the other species, suggesting a different underlying structural strategy. Determination of metal contents showed that the individual concentration of inorganic elements varies, but that the dominant elements are conserved between species. Altogether, this bivalve species comparison suggests some molecular bases for the biomechanical characteristics of byssal fibres that may reflect phylogenetic limitations., Fonds de Recherche du Quebec sur la Nature et les Technologies (FRQNT) [2012-PR-145239]; Natural Sciences and Engineering Research Council of Canada (NSERC, discovery grant)Natural Sciences and Engineering Research Council of Canada [299100]; Tunisian government and Ressources Aquatiques Quebec (Ressources Aquatiques Quebec, Rimouski, Canada), This work was supported by the Fonds de Recherche du Quebec sur la Nature et les Technologies (FRQNT, team project 2012-PR-145239) and the Natural Sciences and Engineering Research Council of Canada (NSERC, discovery grant 299100 to R.T.).Z.B. would like to thank the Tunisian government and Ressources Aquatiques Quebec (Ressources Aquatiques Quebec, Rimouski, Canada) for the award of scholarships. R.T. and I.M. are members of the RAQ.

The simultaneous orientation of poly(1,4-butylene)succinate (PBS) and 4,4′-bis(2-benzoxazolyl)stilbene (BBS) or 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT) in PBS–BBS and PBS–BBT films was investigated during stretching at 80 °C, about 33 °C below the PBS melting temperature. The PBS orientation was first investigated using the 3430 cm−1 infrared band and its order parameter goes from 0.36 at a local strain of 359% for pure PBS to 0.66 in blends containing 6 wt % of BBT at a local draw ratio of ≈350% (or 0.56 with 5 wt % of BBS). At the same time, BBT shows in the same films an orientation parameter reaching a maximum of 0.31 at a local strain of ≈350%, using the 1580 cm−1 band. Since polarized FT-IR was unable to provide the orientation of BBS due to overlapping bands with PBS, polarized fluorescence spectroscopy was then used and reveals an apparent order parameter of 0.32 for BBS monomers (or 0.34 for BBT monomers), but to no orientation of BBT aggregates and BBS excimers. In other words, the two small molecules behave similarly in terms of orientation independently of their molecular shape and packing. BBS and PBS both exhibit a sharp increase of S and when reaching a BBS concentration of ≈0.08 wt %, whereas BBT and PBS show a smooth increase of S and , respectively, in films containing BBT. The sharp increase, or transition in orientation, is accompanied by a conversion of BBS from monomers to excimers, whereas BBT-containing films show a regular increase of the number/size of BBT aggregates. These results indicate that the dye (BBS or BBT) has a profound influence on the orientation of the semi-crystalline polymer (PBS) since its almost doubles at dye concentrations above 0.08 wt %. The results also suggest that the use of a fluorescent probe to follow the polymer chain orientation is not applicable for such systems.

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Dis‐ perse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol% of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE and initial inscription rate reach a maximum when Tg is 25 to 40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol% azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE sixfold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo‐ orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo‐orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

The influence of the supramolecular interaction type—hydrogen bonding, proton transfer, and pure ionic bonding—on photoresponsive behavior, particularly surface relief grating (SRG) inscription, has been investigated using a homopolymer with an ambient temperature glass transition (Tg). To this end, poly(dimethylaminoethyl methacrylate) (PDMAEMA or PDM) of relatively high molecular weight (42K) was complexed at various azo/DM molar ratios with dimethylaminoazobenzene derivatives functionalized by hydroxyl (azoOH) or carboxylic acid (p-methyl red or azoCOOH) groups, and quaternized PDM (PDMQ) was complexed at equimolar ratio with a sulfonated analogue (methyl orange or azoSO3), and the structural and thermal properties of these complexes were determined. SRG inscription on spin-coated films was found to be possible because complexation increases the Tg above ambient. The efficiency of SRG inscription on spin-coated films, which increases with azo content, is highest for the purely ionic azoSO3/PDMQ complex despite its very high Tg, while the proton transfer azoCOOH/PDM complexes, involving ionic and H-bonding with acid-salt structures, show somewhat more efficient SRG inscription than do the purely hydrogen-bonded azoOH/PDM complexes, and this despite some azoCOOH crystallization at the highest molar ratios. These findings clarify the comparative effectiveness of different supramolecular bond types on SRG inscription and provide a useful guide for the design of supramolecular photoresponsive polymers for SRG applications.

Supramolecular polymer complexes with small molecules are self-assembled through non-covalent interactions and have been proposed for a wide variety of applications in materials science and nanoscience. Our research group has recently shown the possibility of forming highly ordered nanofibers of supramolecular complexes in their thermodynamically stable state using the electrospinning technique. The ultrafast solvent evaporation rate of electrospinning made possible the in-depth characterization of complexes that had never been prepared in their pure state before because of kinetic issues associated with their formation by conventional approaches. The improved understanding of the formation mechanism allowed us to extend the concept to other techniques featuring a fast solvent evaporation rate, such as electrospray and spin-coating. In this article, we review our most significant contributions in this research field.