High-sensitivity fiber optic Fabry-Perot ultrasonic sensor based on a grooved silicon diaphragm for partial discharge detection.

An extrinsic fiber optic Fabry-Perot interferometric (EFPI) ultrasonic sensor based on a grooved silicon diaphragm for partial discharge (PD) detection has been proposed. The size of the groove is determined by finite element simulation, which allows the resonant frequency of the sensor to meet the requirements of PD ultrasonic detection and improves the sensitivity of the sensor by 5.07 times compared with that based on a traditional circular diaphragm. The microelectro-mechanical system process is used to fabricate the diaphragm on a silicon-on-insulator wafer, and the prepared diaphragm has a grooved section with a diameter of 829.34 µm and a thickness of only 2.09 µm. At its resonant frequency of 61.5 kHz, the acoustic pressure sensitivity of the sensor is 172.42 mV/Pa. The ultrasonic signal detection capability of the sensor is verified in the PD experiment. Furthermore, the characteristics of the corona discharge are successfully manifested based on the ultrasonic waves detected by the EFPI sensor. It is demonstrated that the proposed sensor is suitable for PD detection due to its high sensitivity, simple production process, and good resistance to environmental interference.

Self-Healing, Thermadapt Triple-Shape Memory Ionomer Vitrimer for Shape Memory Triboelectric Nanogenerator.

Benefiting from the associative exchange reaction, vitrimers could be deformed to various shapes while maintaining the integrity of the network, thus being regarded as promising candidates for shape memory polymers. However, it is still a challenge to design the highly desired smart electronic devices with triple and multishape memory performances through a facile method. Here, a novel dual-cross-linked poly(acrylonitrile-co-butyl acrylate-co-hydroxyethyl methacrylate-co-zinc methacrylate) (Zn-PABHM) copolymer was developed via a facile and one-pot free radical polymerization strategy. Ionic cross-linking, the transcarbamoylation reaction, and glass transition were used to fix the permanent shape and two temporary shapes of the obtained ionomer vitrimer, respectively. The thermomechanical and stress relaxation performances of Zn-PABHM vitrimer can be customized by tuning the proportion of the chemical cross-linking and physical cross-linking knots. Furthermore, the Zn-PABHM was employed to construct a shape memory triboelectric nanogenerator, which demonstrates distinctive performance and tunable electrical outputs (37.4-96.0 V) due to variable contact areas enabled by triple shape memory effects. Consequently, the triple-shape memory ionomer vitrimer obtained via a facile and one-pot synthetic strategy has great potential in smart multifunctional electronic devices.

Mechanical stimuli-induced multiple photophysical responsive AIEgens with high contrast properties.

A new cyano-distyrylbenzene derivative with a mechano-force induced high contrast transition in color and emission was demonstrated here. Under mechanical stimuli, the emission peak can undergo a large wavelength shift from 440 nm to 650 nm, while the appearance color can switch from white to pink.

Fluorescence to multi-colored phosphorescence interconversion of a novel, asterisk-shaped luminogen via multiple external stimuli.

We designed and characterized an asterisk-shaped luminogen, hexakis(pyridin-4-ylthio)benzene (HPTB). Via external stimuli such as CH3OH, H+, and Ag+, HPTB's luminogenic character transitioned from blue fluorescence to green, yellow, and orange phosphorescence. Results showed that this interconversion was a reversible process that was also reproducible in liquid and in the solid state.

Dual Cross-linked Vinyl Vitrimer with Efficient Self-Catalysis Achieving Triple-Shape-Memory Properties.

As an emerging class of dynamic cross-linked network, vitrimers have attracted much attention due to the combination of mechanical advantages of thermosets and recyclability of thermoplastics at an elevated temperature. In particular, most vitrimers with multi-shape memory properties usually involve more than one thermal transition or molecular switch, which might pose a challenge for facile sample fabrication and potentially limits their applications. In pursuit of a more universal and simple route, utilizing commercially available and inexpensive reagents to prepare shape-memory vitrimers with dual cross-linked network from vinyl monomer-derived prepolymers is reported here. Copolymerization of desired vinyl monomers gives prepolymers containing carboxyl and zinc carboxylate groups, which are later converted into vitrimers in a single step by post-curing with diglycidylether of bisphenol A. The Zn2+ ions can not only act as physical crosslinking points through ionic coordination interactions, thus providing the triple-shape-memory properties, but also play the role of catalyst to activate transesterification in the dynamic covalent network. This new self-catalyzed vitrimer has excellent transesterification efficiency, triple-shape-memory properties, and can be sufficiently healed and reprocessed at an elevated temperature. The proposed molecular design of self-catalyzed materials opens a new avenue toward commercially relevant fabrication of high-performance vitrimers with multiple shape-memory properties.

High-performance polyurethane nanocomposites based on UPy-modified cellulose nanocrystals.

Densely H-bonding assemblies are the key strategy found by nature to enhance the rupture strength of natural polymers without sacrificing their toughness, such as spider silk, while it still remains a great challenge using such intriguing strategy to prepare high-performance synthesized polymer or biopolymer enhanced polymer nanocomposites. To address this challenge, we report here a bio-inspired strategy using densely H-bonding assembly for facile fabrication of high performance polyurethane (PU) nanocomposites reinforced by hydroxyl-rich cellulose nanocrystals (CNCs) functionalized with 2-ureido-4-[1 H]-pyrimidinone motifs (CNC-UPy) containing self-complementary hydrogen bonds. These PU/CNC-UPy nanocomposites showed remarkably improved mechanical strength without sacrificing the elongation at break and toughness compared to pure PU matrix. Differential scanning calorimetry(DSC) results indicated that CNC-UPy could induce the formation of long range ordering of hard segment domains, due to the strong hydrogen bonding interactions between UPy motifs attached on CNC-UPy and PU matrix. Furthermore, wide angle X-ray diffraction (WAXD) measurements demonstrated that the strain-induced crystallization (SIC) was enhanced significantly by introducing CNC-UPy into PU, leading to a large stress at break. The enhanced interfacial H-bonding interactions between CNC and PU though UPy anchoring could overcome the inherent trade-off between the stiffness and toughness of polymer composites. The proposed bio-inspired strategy using densely H-bonding assembly will be with more extensive application prospects.