Thermo-Induced Single-Crystal-to-Single-Crystal Transformations and Photo-Induced [2+2] Cycloaddition Reactions in Polymorphs of Chalcone-Based Molecular Crystals: Multi-Stimuli Responsive Actuators

The polymorphs of 2ClChMe-4 in Form I (ribbon-like crystal) and Form II (block-like crystal) were prepared, and they exhibited curling/flipping and expansion upon heating on account of single-crystal-to-single-crystal transformations. The irreversible phase transformations occurred separately at 53.2 °C and 57.8 °C for the crystals in Form I and Form II, during which the molecular conformation of 2ClChMe-4 changed and the molecules slipped along the (100) plane. Movement at the molecular level resulted in changes of cell parameters, which in turn led to macroscopic motions of the crystals upon heating. Additionally, the ribbon-like crystals of 2ClChMe-4 showed photo-induced bending driven by [2+2] cycloaddition. Accordingly, an actuator showing reversible bending behavior was fabricated triggered by light and heat successively. Like biomimetic self-actuators, such multi-stimuli mechanical responsive molecular crystals might have potential applications in soft robots, artificial muscles and microfluidic systems.     

Photoswitchable Conjugated Oligoelectrolytes for a Light-Induced Change of Membrane Morphology

The synthesis of a new conjugated oligoelectrolyte (COE), namely DSAzB, is described, which contains a conjugated core bearing a diazene moiety in the center of its electronically delocalized structure. Similar to structurally related phenylenevinylene-based COEs, DSAzB readily intercalates into model and natural lipid bilayer membranes. Photoinduced isomerization transforms the linear trans COE into a bent or C-shape form. It is thereby possible to introduce DSAzB into the bilayer of a cell and disrupt its integrity by irradiation with light. This leads to controlled permeabilization of membranes, as demonstrated by the release of calcein from DMPG/DMPC vesicles and by propidium iodide influx experiments on S. epidermidis. Both experiments support that the permeabilization is selective for the light stimulus, highly efficient, and repeatable. Target-selective and photoinduced actions demonstrated by DSAzB may have broad applications in biocatalysis and related biotechnologies.     

Bistable Structures for Advanced Functional Systems

Bistable mechanical systems having two local minima of potential energy can rest in either of the two stable equilibrium states in the absence of external loadings. A snap-through action may occur under suitable stimuli and/or loading, during which such systems exhibit distinct properties from linear structures. Such kinds of structures have been widely exploited for designing advanced functional systems for a variety of applications. Here, the advances of bistable structures are summarized for novel advanced functional systems, including actuators, energy harvesters, microelectromechanical systems (MEMS), robotics, energy absorbers, and programmable devices as well as metamaterials. The controllable snap-through motions are highlighted in the nonlinear structures of bistability/multistability. Finally, the major principles, structures, pros and cons, and the future research directions along with its challenges are discussed.     

Durable and highly selective tungsten-substituted MFI metallosilicate catalysts for the methanol-to-propylene process by designing a novel feed-supply technique

For the catalytic reaction of methanol to propylene (MTP), conventional H-ZSM-5 and W-substituted MFI metallosilicate catalysts were successfully synthesized using a hydrothermal method. The catalysts were properly characterized by several techniques. For comparison of the catalytic lifetime, feedstock of MTP was provided by both a conventional system and a novel feed-supply technique. The novel technique used the piezoelectric ultrasonic effect. It was revealed that feed composition via novel feed-supply technique remained totally constant, whereas with conventional system it relatively changed. Complete methanol conversion, higher propylene yield of 54.3%, greater light olefin yield of 85.2%, and longer-term catalytic lifetime of 101 h were productively obtained for H-W(250)AlMFI catalyst using a novel method for provision of feed. The better performance of this catalyst can be attributed to adequate content of tungsten, appropriate mesoporosity, sufficient strength of acidic sites, and stable feed composition of the novel feed-supply technique. Furthermore, the MTP process was miniaturized by the piezoelectric ultrasonic device.     

Autotuning of Vibrational Strong Coupling for Site-Selective Reactions

Site-selective chemistry opens new paths for the synthesis of technologically important molecules. When a reactant is placed inside a Fabry–Perot (FP) cavity, energy exchange between molecular vibrations and resonant cavity photons results in vibrational strong coupling (VSC). VSC has recently been implicated in modified chemical reactivity at specific reactive sites. However, as a reaction proceeds inside an FP cavity, the refractive index of the reaction solution changes, detuning the cavity mode away from the vibrational mode and weakening the VSC effect. Here we overcome this issue, developing actuatable FP cavities to allow automated tuning of cavity mode energy to maintain maximized VSC during a reaction. As an example, the site-selective reaction of the aldehyde over the ketone in 4-acetylbenzaldehyde is achieved by automated cavity tuning to maintain optimal VSC of the ketone carbonyl stretch during the reaction. A nearly 50 % improvement in site-selective reactivity is observed compared to an FP cavity with static mirrors, demonstrating the utility of actuatable FP cavities as microreactors for organic chemistry.     

Micro–macro linear piezoelectric motor based on self-moving cell

This paper deals with the development of a piezoelectric linear motor that can control macro and micro movements. Concept of the motor is based on a self-moving cell, which consists of an elastic shell structure and a piezoelectric stack actuator. Three cells are connected in series and by activating piezoelectric actuators in these cells, macro movement can be achieved. Since these cells are fit into a guideway with interference, this motor can possess a high stall force and fail-safe lock. When one piezoelectric actuator is activated by open loop control with hysteresis compensation, micro movement can be obtained. Design of self-moving cell structure, fabrication, and control of the motor for macro and micro movements are explained. The maximum moving velocity of 1.05 mm/s and the maximum force of 4.3 N were observed. The possibility of nano scale movement was demonstrated by taking into account the hysteresis compensation of the piezoelectric actuator.     

一种新型MEMS离面驱动器的设计与分析

提出了一种基于静电排斥效应的MEMS离面驱动器,在消除静电拉入效应的同时得到了较大的静电排斥力。驱动器主要由三个下极板、一个上极板和弹簧梁组成。首先进行了静电排斥现象原理的分析,然后对弹簧梁中有和没有横梁时的弹性系数和模态进行了详细分析和对比,最后对驱动器的行程、驱动力、频率响应和带宽等性能进行了分析。结果表明,存在横梁时结构更加稳定,施加200V电压时,结构有2.5μm的位移和28μN的驱动力,而且带宽约为7kHz。该驱动器可运用于光通信和空间光调制等领域。     

Theory of 2×2 switch based on electro-optic and piezoelectric effects in photorefractive LiNbO3 crystal

Based on the electro-optic and piezoelectric effects, the principle of a 2×2 bypass-exchange switch in photorefractive LiNbO₃ crystal is discussed. In photorefractive volume grating, the Bragg condition can be changed by applying a field during readout. That is, by applying a specific field E_s or zero, the diffraction efficiency will be 0 or 1, respectively and this property can be used to realize the bypass or exchange operation of the switch. In this paper, considering both the piezoelectric and electro-optic effects caused by the applied electric field, we analyzed relations of both the specific field and the incident intensity ratio with respect to the writing angles and polarizations of writing beams.