Morphology-Mediated Photoresponsive and Fluorescence Behaviors of Azobenzene-Containing Block Copolymers

We investigated the relationship between the self-assembled morphology of poly­(<i>tert</i>-butyl acrylate)-<i>block</i>-poly­(6-[4-(4′-methoxyphenylazo)­phenoxy]­hexyl methacrylate) (P<i>t</i>BA-<i>b</i>-PAzoMA) block copolymers and their photoresponsive and fluorescence behaviors. The morphology of P<i>t</i>BA-<i>b</i>-PAzoMA copolymers was manipulated by dissolving them in mixed dimethylformamide (DMF)/hexanol solvents. When P<i>t</i>BA-<i>b</i>-PAzoMA was dissolved in DMF-rich (neutral) solvents, a favorable interaction between the DMF molecules and both blocks resulted in a random-coiled conformation. The unconfined morphology facilitated the formation of both nonassociated and head-to-head organized azobenzene mesogens, which promoted fluorescence emission. When hexanol, a P<i>t</i>BA-selective solvent, was added to DMF, the solvency of P<i>t</i>BA-<i>b</i>-PAzoMA worsened, leading to its assembly into micelles, with PAzoMA in the micelle core. The confinement of azobenzene moieties in the micelle core hindered their <i>trans</i>-to-<i>cis</i> photoisomerization, thereby considerably decreasing the kinetics of photoisomerization and the population of <i>cis</i> isomers. Additionally, a nanoconfined geometry resulted in compactly packed chromophores, causing fluorescence loss. When P<i>t</i>BA-<i>b</i>-PAzoMA was exposed to UV light, the increased number of <i>cis</i> isomers hampered the closely packed mesogens, resulting in a substantial enhancement of fluorescence emission. When the mole fraction of the PAzoMA block was increased, P<i>t</i>BA-<i>b</i>-PAzoMA formed clusters, causing the slow kinetics of photoisomerization and fluorescence quenching

Biomineralization of Calcium Phosphate and Calcium Carbonate within Iridescent Chitosan/Iota-Carrageenan Multilayered Films

This work systematically explores the biomineralization of calcium phosphate (CaP) and carbonate (CaCO₃) within chitosan/iota-carrageenan multilayer films. Multilayer films of chitosan and iota-carrageenan (up to 128-coupled layers) were prepared on glass substrates by a layer-by-layer dip-coating technique. Cryo-scanning electron microscopy revealed dense interfaces between the chitosan and iota-carrageenan layers with thicknesses in the range 250 and 350 nm in the hydrated state, accounting for the iridescent nature of multilayer films when wet. Immersion of the multilayered films in simulated body fluid or simulated seawater at 25 °C resulted in the mineralization of CaP and CaCO₃, respectively, at the interfaces between the biopolymer layers and modified the iridescence of the films. Lamellar scattering features in small-angle neutron scattering measurements of the mineralized films provided evidence of the localized mineralization. Further evidence of this was found through the lack of change in the dynamic and static correlation lengths of the polymer networks within the bulk phase of the chitosan and iota-carrageenan layers. CaP mineralization occurred to a greater extent than CaCO₃ mineralization within the films, evidenced by the higher lamellar density and greater rigidity of the CaP-mineralized films. Results provide valuable new insights into CaP and CaCO₃ biomineralization in biopolymer networks

Molecularly Engineered Intrinsically Healable and Stretchable Conducting Polymers

Advances in stretchable electronics concern engineering of materials with strain-accommodating architectures and fabrication of nanocomposites by embedding a conductive component into an elastomer. The development of organic conductors that can intrinsically stretch and repair themselves after mechanical damage is only in the early stages yet opens unprecedented opportunities for stretchable electronics. Such functional materials would allow extended lifetimes of electronics as well as simpler processing methods for fabricating stretchable electronics. Herein, we present a unique molecular approach to intrinsically stretchable and healable conjugated polymers. The simple yet versatile synthetic procedure enables one to fine-tune the electrical and mechanical properties without disrupting the electronic properties of the conjugated polymer. The designed material is comprised of a hydrogen-bonding graft copolymer with a conjugated backbone. The morphological changes, which are affected by the composition of functional side chains, and the solvent quality of the casting solution play a crucial role in the synthesis of highly stretchable and room-temperature healable conductive electronic materials