Easy Processable Photomechanical Thin Film Involving a Photochromic Diarylethene and a Thermoplastic Elastomer in Supramolecular Interaction.

A novel supramolecular photoactuator in the form of a thin film of centimetric size has been developed as an alternative to traditional liquid crystal elastomers (LCE) involving azobenzene (AZO) units or photochromic microcrystals. This thin film is produced through spin coating without the need for alignment or crosslinking. The photoactuator combines a photochromic dithienylethene (DTE) functionalized with ureidopyrimidinone (UPy) units, and a telechelic thermoplastic elastomer, also functionalized with UPy, allowing quadruple hydrogen bonding between the two components. Upon alternating ultraviolet (UV) and visible light exposure, the film exhibits reversible bending and color changes, studied using displacement and absorption tracking setups. For the first time, the photomechanical effect (PME) is quantitatively correlated with photochromism, showing that DTE units drive the movement under both UV (photocyclization) and visible (photoreversion) light. In situ illumination techniques reveal that the PME arises from photoinduced strain within 160 nm UPy-bonded DTE domains, which expand and contract by approximately 50% under UV and visible light, respectively. The semicrystalline nature of the elastomer and a robust supramolecular network connecting both components are critical in converting microscopic photostrain into macroscopic actuation.

New Insight into Nanoscale Identification of the Polar Axis Direction in Organic Ferroelectric Films.

Ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-co-TrFE)] thin films have been deposited by spin-coating onto the Bi0.5Na0.5TiO3(BNT)/LNO/SiO2/Si heterostructure. The copolymer microstructure investigated by using grazing-incidence wide-angle X-ray diffraction (GIWAXD) and deduced from the (200)/(110) reflections demonstrates that the b-axis in the P(VDF-co-TrFE) orthorhombic unit cell is either in the plane or out of the plane, depending on the face-on or on the two types of edge-on (called I and II) lamellar structures locally identified by atomic force microscopy (AFM). For edge-on I lamellae regions, the electroactivity (dzzeff ∼ -50.3 pm/V) is found to be twice as high as that measured for both edge-on II or face-on crystalline domains, as probed by piezoresponse force microscopy (PFM). This result is directly correlated to the direction of the ferroelectric polarization vector in the P(VDF-co-TrFE) orthorhombic cell: larger nanoscale piezoactivity is related to the b-axis which lies along the normal to the substrate plane in the case of the edge-on I domains. Here, the ability to thoroughly gain access to the as-grown polar axis direction within the edge-on crystal lamellae of the ferroelectric organic layers is evidenced by combining the nanometric resolution of the PFM technique with a statistical approach based on its spectroscopic tool. By the gathering of information at the nanoscale, two orientations for the polar b-axis are identified in edge-on lamellar structures. These findings contribute to a better understanding of the structure-property relationships in P(VDF-co-TrFE) films, which is a key issue for the design of future advanced organic electronic devices.

Solvent-Free Design of Biobased Non-isocyanate Polyurethanes with Ferroelectric Properties.

Increasing energy autonomy and lowering dependence on lithium-based batteries are more and more appealing to meet our current and future needs of energy-demanding applications such as data acquisition, storage, and communication. In this respect, energy harvesting solutions from ambient sources represent a relevant solution by unravelling these challenges and giving access to an unlimited source of portable/renewable energy. Despite more than five decades of intensive study, most of these energy harvesting solutions are exclusively designed from ferroelectric ceramics such as Pb(Zr,Ti)O3 and/or ferroelectric polymers such as polyvinylidene fluoride and its related copolymers, but the large implementation of these piezoelectric materials into these technologies is environmentally problematic, related with elevated toxicity and poor recyclability. In this work, we reveal that fully biobased non-isocyanate polyurethane-based materials could afford a sustainable platform to produce piezoelectric materials of high interest. Interestingly, these non-isocyanate polyurethanes (NIPUs) with ferroelectric properties could be successfully synthesized using a solvent-free reactive extrusion process on the basis of an aminolysis reaction between resorcinol bis-carbonate and different diamine extension agents. Structure-property relationships were established, indicating that the ferroelectric behavior of these NIPUs depends on the nanophase separation inside these materials. These promising results indicate a significant potential for fulfilling the requirements of basic connected sensors equipped with low-power communication technologies.

Nanoscale Investigations of α- and γ-Crystal Phases in PVDF-Based Nanocomposites.

The impact of carbon nanotube (CNT) incorporation into semicrystalline poly(vinylidene fluoride), PVDF, was investigated at both the macro and nanoscales. A special effort was devoted to probe the local morphology and the mechanical, ferroelectric, piezoelectric, and electrical conductivity response by means of atomic force microscopy. Incorporation of CNTs mainly induces the development of the polar γ-phase, and as a consequence, the coexistence of the γ-phase with the most stable nonpolar α-phase is observed. A maximum γ-phase content is reached at 0.7 wt % CNT loading. The spherulitic morphology of the PVDF α-phase is assessed, in conjunction with the lack of any ferroelectric response, while the presence of the polar γ-phase is confirmed, owing to clear piezoresponse signals. Local piezoelectric measurements on γ-phase domains yield a maximum effective coefficient | d33| ≈ 13 pm/V, thus underlining the potential for applications of such functional PVDF-based nanocomposites in advanced piezoelectric devices. An increase in macroscopic conductivity with CNT content is observed, with a percolation threshold achieved for a composition close to 0.7 wt %. Nanoscale investigation of the electrical conductivity confirms the presence of some infinite CNT cluster homogeneously distributed over the surface. The macroscopic viscoelastic behavior of the composite reflects the reinforcing effect of CNTs, while the nanomechanical characterization yields a local contact modulus of the γ-phase domains larger than that of its α-phase counterpart, in agreement with the fact that the CNTs act as γ-phase promoters and subsequently reinforce the γ-domains.