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Compared with normal stimulus such as light and heat, ultrasonic possesses much deeper penetration into tissues and organs and has lower scattering in heterogeneous systems as a noninvasive stimulus. Reversible addition‐fragmentation chain‐transfer polymerization (RAFT) in aqueous media is performed in a commercial ultrasonic wash bath with 40 kHz frequency ultrasonic, in the presence of piezoelectric tetragonal BaTiO3 (BTO) nanoparticles. Owing to the electron transfer from BTO under the ultrasonic action, the water can be decomposed to produce hydroxyl radical (HO•) and initiate the RAFT polymerization (piezo‐RAFT). The piezo‐RAFT polymerization exhibits features of controllable and livingness, such as linear increase of molar mass and narrow molar mass distributions (Mw/Mn < 1.20). Excellent temporal control of the polymerization and the chain fidelity of polymers are illustrated by "ON and OFF" experiment and chain extension, separately. Moreover, this ultrasonic‐driven piezoelectric‐induced RAFT polymerization in aqueous media can be directly used for the preparation of piezoelectric hydrogel which have potential application for stress sensor. [ABSTRACT FROM AUTHOR]

Azobenzene (Azo) liquid‐crystalline polymers are intriguing due to their unique photo‐induced isomerization and supramolecular chirality. However, clarification on multicomponent chiral induction towards Azo polymers remains ambiguous and challenging. Herein, chiral solvents and amines were employed to control the chiroptical activity of achiral Azo polymers. Methyl L‐/D‐lactate was added as the poor solvent and chiral inducer to achieve the first chiral induction in Azo aggregates. Chiral amines were utilized for the second chiral induction based on the acid–base interactions between the carboxyl groups of polymers and amines. The chiral enhancement and inversion of Azo units could be observed through the synergistic or antagonistic effect between solvents and amines. The impacts of solvent, chemical structures, feed ratio, enantiomeric excess, and temperature on supramolecular chirality were systematically studied. Furthermore, this system displayed the chiroptical switching property and chiral recovery under reversible irradiation. [ABSTRACT FROM AUTHOR]

Liquid metal (LM) and liquid metal alloys (LMs) possess unique physicochemical features, which have become emerging and functionalized materials that are attractive applicants in various fields. Herein, uniform LM nanodroplets armored by carbon dots (LMD@CDs) were prepared and exhibited high colloidal stability in various solvents, as well as water. After optimization, LMD@CDs can be applied as functional additives for the 3D/4D printing of hydrogel and cross‐linked resin through digital light processing (DLP). The light absorption of LMD@CDs not only improved the printing accuracy, but also led to the cross‐linking density differential during the post‐curing process. Base on the cross‐linking density differential of soft hydrogel and photothermal performance of the LM, the 3D printed objects can exhibit stimulus responses to both water and laser irradiation. Additionally, the CDs shell and LM core of LMD@CDs provide the printed objects interesting photoluminescence and electric conductivity capabilities, respectively. We deduce this versatile 3D/4D printing system would provide a new platform for the preparation of multi‐functional and stimuli‐responsive advance materials. [ABSTRACT FROM AUTHOR]

A high incidence of traffic accidents is often observed in freeway exit ramp areas. Slowing down, wandering, and changing lanes suddenly and continually in a short interval near the exit ramp are important reasons for accidents. Helping drivers start changing lanes sooner and more efficiently in freeway exit ramp areas is a feasible solution to vehicle interweaving. This paper aims to optimize the current guiding sign system and improve drivers' lane-changing behavior before the exit ramp. Three guiding sign optimization measures (sign symbols, ground signs and voice prompts) had been considered before five guiding sign plans were made for driving simulation experiments: original sign (OS) plan, new type sign (NTS) plan, ground guiding sign (GOS) plan, voice prompt (VOS) plan, and voice-ground sign (VGOS) plan. The decisions, reactions, and operation processes of 43 Chinese drivers were compared to confirm the optimal guiding sign plan. The results showed that updating sign symbols, adding ground signs and voice prompts all contributed to the drivers' shorter response time, earlier arrival at the lane-changing location, higher average speed and greater longitudinal distance of lane-changing. These findings can help freeway designers optimize the guiding sign system for freeway exit ramps. [ABSTRACT FROM AUTHOR]

Shape memory polyamide elastomers have attracted large attention owing to a variety of favorable properties (e.g., designable chemical structure, good thermal stability, flexibility, and elasticity, et al). However, the polyamide elastomer reported recently still lack good mechanical property. In the present work, a new type of shape memory thermoplastic polyamide elastomer (TPAE), composed of long carbon chain PA1212 and polytetramethylene ether glycol (PTMEG), is synthesized through two‐step melt polycondensation, which is named as poly(ether‐b‐amide) (PEBA). The chemical structure of PEBA is confirmed by FTIR results and it also shows excellent mechanical properties. PEBA, possessing two melting temperatures, stay in microphase separation among PTMEG soft domains and PA1212 hard domains that are amorphous and α crystal, respectively. Furthermore, PEBA can fix a temporary shape after the heated strip is twisted and cooled down and then recover to the original shape after secondary heating, which is attributed to the fixing force provided by PTMEG domains and entropy elasticity of physically cross‐linked PA1212 domains, respectively. Besides, PEBA elastomer can be reshaped between ≈190 and ≈380 °C and it also has shape memory behavior. This new kind of TPAE proposes a new smart material for sensors and soft robotics. [ABSTRACT FROM AUTHOR]

Although tremendous advancement regarding the highly stable metal halide perovskite nanocrystals (PNCs) has been achieved, previous studies were primarily focused on green light-emitting PNCs (i.e., bromine-based PNCs). The stability of chlorine-based PNCs with a violet or blue emission property was still lagging behind that of their bromine-based counterparts. Herein, a nondemanding and versatile strategy for in situ encapsulating all-inorganic chlorine-based PNCs with multifold exceptionally high stabilities was presented. Well-ordered mesoporous silica enabled the confined growth of PNCs in its pores followed by the porosity sealing by tetramethyl orthosilicate hydrolysis, thereby rendering full encapsulation of chlorine-based PNCs in dense silica that originated from high-temperature calcination. This judiciously designed structure imparted enclosed violet/blue emitting PNCs impart with outstanding long-term stability (>1.5 year) with high photoluminescence quantum yield (i.e., 30.4%) in pure water as the result of complete isolation of PNCs from detrimental stimuli, eventually leading to the application in the white light-emitting diode device. [ABSTRACT FROM AUTHOR]

Multiple and two‐way reversible shape memory polymers (M/2W‐SMPs) are highly promising for many fields due to large deformation, lightweight, strong recovery stress, and fast response rates. Herein, a semi‐crystalline block poly(urethane‐urea‐amide) elastomers (PUUAs) are prepared by the copolymerization of isocyanate‐terminated polyurethane (OPU) and amino‐terminated oligomeric polyamide‐1212 (OPA). PUUAs, composed of OPA as stationary phase and PTMEG as reversible phase, exhibit excellent rigidity, flexibility, and resilience, and cPUUA‐C7‐S25 exhibits the best tensile property with strength of 10.3 MPa and elongation at break of 360.2%. Besides, all the PUUAs possess two crystallization/melting temperatures and a glass transition temperature, which endow PUUAs with multiple and reversible two‐way shape memory effect (M/2W‐SME). Physically crosslinked PUUA‐C0‐S25 exhibits excellent dual and triple shape memory, and micro chemically crosslinked cPUUA‐C7‐S25 further shows quadruple shape memory behavior. Additionally, both PUUA‐C0‐S25 and cPUUA‐C7‐S25 have 2W‐SME. Intriguingly, cPUUA‐C7‐S25 can achieve a higher temperature (up to 165 °C) SME, which makes it suitable for more complex and changeable applications. Based on the advantages of M/2W‐SME, a temperature‐responsive application scenario where PUUAs can transform spontaneously among different shapes is designed. These unique M/2W‐SME and high‐temperature SME will enable the applications of high‐temperature sensors, actuators, and aerospace equipment. [ABSTRACT FROM AUTHOR]