4D Printing Dielectric Elastomer Actuator Based Soft Robots

4D printing is an emerging technology that prints 3D structural smart materials that can respond to external stimuli and change shape over time. 4D printing represents a major manufacturing paradigm shift from single-function static structures to dynamic structures with highly integrated functionalities. Direct printing of dynamic structures can provide great benefits (e.g., design freedom, low material cost) to a wide variety of applications, such as sensors and actuators, and robotics. Soft robotics is a new direction of robotics in which hard and rigid components are replaced by soft and flexible materials to mimic mechanisms that works in living creatures, which are crucial for dealing with uncertain and dynamic tasks. However, little research on direct printing of soft robotics has been reported. Due to the short history of 4D printing, only a few smart materials have been successfully 4D printed, such as shape memory and thermo-responsive polymers, which have relatively small actuation strains (up to ~8%). In order to produce the large motion, dielectric elastomer actuator (DEA), a sheet of elastomer sandwiched between two compliant electrodes and known as artificial muscle for its high elastic energy density and capability of producing large strains (~200%), is chosen as the actuator for soft robotics. Little research on 3D printing silicone DEA soft robotics has been done in the literature. Thus, this thesis is motivated by applying the advantages in 3D printing fabrication methods to develop DEA soft robotics. The ultimate research goal is to demonstrate fully printed DEA soft robots with large actuation. In Chapter 1, the research background of soft robotics and DEAs are introduced, as well as 3D printing technologies. Chapter 2 reports the rules of selecting potentially good silicone candidates and the printing process with printed material characterizations. Chapter 3 studies the effects of pre-strain condition on silicone material properties and the performance of DEA configurations, in order to obtain large actuation strain. In Chapter 4, two facial soft robots are designed to achieve facial expressions as judged by a smiling lip and expanding pupils based on DEA actuation. Conclusions and future developments are given in chapter 5 and 6, respectively

Development of Novel Battery Materials for Lithium-Ion Batteries and Beyond

As fossil fuels are depleting and causing environmental issues, it becomes imperative to widely implement renewable energies (e.g., solar and wind power). In this context, electrical energy storage (EES) systems are essential to accommodate the intermittent supply and uneven distribution of renewable energies. To this end, high-energy-density EES devices are highly demanded, such as rechargeable batteries. This dissertation presents my efforts in developing novel battery materials for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and solidstate lithium batteries (SSLBs). These efforts include electrochemical evaluations of battery materials, surface modifications of electrodes via atomic layer deposition (ALD), and advanced characterizations of batteries materials. In this dissertation, my first effort invested on the growth of ZnO nanofilms via ALD. ALD technique possesses some unrivaled merits, including atomic-scale controllability, excellent uniformity and conformality, and the accessibility of a large variety of materials. In the past decade, it has been widely used for surface-modifying battery electrodes. This study investigated growth characteristics and underlying mechanisms of ALD ZnO nanofilms using diethylzinc and water precursors. The temperature-controllable growth and crystal-orientation of ALD ZnO films were disclosed. This study offered key understanding and preliminary preparation for the following study to surface-modify electrode materials. A subsequent effort was focused on developing a novel anode for SIBs. SIBs have attracted an ever-growing research interest, due to their cost-effectiveness as large-scale stationary EES devices. However, compared with LIBs, SIBs are significantly hindered by the lack of suitable anodes. In this study, Cu2S was chosen for high capacity and fast-charge capability. The nitrogendoped graphene (NG) wrapped Cu2S (Cu2S@NG) composite anode exhibited stable cyclabilityand excellent rate capability. The electrochemical mechanism was investigated using synchrotronbased X-ray techniques. Whereas the parasitic reactions at the electrode/electrolyte interface continuously deteriorated performance, which could be resolved by surface modifications via ALD. In the sequential effort to enhance interfacial stability of Cu2S@NG anode, the electrochemically inactive Al2O3 via ALD was selected as the coating material. A 6-nm ultrathin Al2O3 coating could improve the interfacial stability of the Cu2S@NG anode and thereby enhance its electrochemical performance with the highest capacity reported to date. Additionally, this dissertation includes an effort in investigating a promising solid-state electrolyte (SSE), Li7La3Zr2O12 (LLZO). Conventionally, flammable liquid-organic electrolytes have been used in LIBs but induced some safety issues (e.g., fires and explosions). In this regard, SSEs are highly regarded to replace liquid organic electrolytes. LLZO is among the most promising SSEs with high ionic conductivity (~10-3 S cm-2 at room temperature) and high stability with Li metal anode. Nevertheless, LLZO’s stability in the ambient storage is challenging, causing deteriorated ionic conductivity and interfacial instability. This study investigated the structural and stoichiometric reversibility of air-aged LLZO during heat treatment. In addition, the correlation between restoration degree and dopant chemistry was unveiled. In summary, the contributions in this dissertation provide critical understandings to electrochemical mechanisms and degradation causes of novel electrode and electrolyte materials and demonstrate the vital surface modification route via ALD for enhanced performance

Perovskite heterojunction based on CH3NH3PbBr3 single crystal for high-sensitive self-powered photodetector

Perovskite single crystals exhibit extraordinary optoelectronic performances due to their advantages such as low trap-state densities, long carrier diffusion, and large absorption coefficient, and thus, photodetectors based on perovskite single crystals have attracted much research interest. Unlike the reported one-component single-crystal perovskite photodetectors, here, we have developed a facile two-step approach to fabricate a core-shell heterojunction based on the CH3NH3PbBr3 single crystal. A photodetector made of the as-prepared perovskite heterojunction renders the feature of self-power attributed to a built-in electric field in the junction and exhibits a wavelength-dependent responsivity with a peak responsivity up to 11.5 mA W−1 under 450 nm irradiation at zero bias, which is one order of magnitude higher than the CH3NH3PbBr3 single crystal and shows a maximum external quantum efficiency of 3.17%, also higher than the reported 0.2% of the CH3NH3PbBr3 single crystal. Our work may lead to more efficient self-powered heterojunction systems based on perovskite single crystals.Publisher PDFPeer reviewe

Expression of pathogenesis related genes in response to salicylic acid, methyl jasmonate and 1-aminocyclopropane-1-carboxylic acid in Malus hupehensis (Pamp.) Rehd

<p>Abstract</p> <p>Background</p> <p>Many studies have been done to find out the molecular mechanism of systemic acquired resistance (SAR) in plants in the past several decades. Numbers of researches have been carried out in the model plants such as arabidopsis, tobacco, rice and so on, however, with little work done in woody plants especially in fruit trees such as apple. Components of the pathway of SAR seem to be extremely conserved in the variety of species. <it>Malus hupehensis</it>, which is origin in China, is strong resistance with rootstock. In the study, we attempted to make the expression pattern of pathogenesis related (PR) genes which were downstream components of the SAR pathway in response to salicylic acid(SA), methyl jasmonate(MeJA) and 1-aminocyclopropane-1-carboxylic acid(ACC) in <it>Malus hupehensis</it>.</p> <p>Findings</p> <p>In order to analyze the expression pattern, the partial sequence of three PR genes from <it>Malus hupehensis</it>, <it>MhPR1</it>, <it>MhPR5 </it>and <it>MhPR8 </it>was isolated. These three PR genes were induced by SA, MeJA and ACC. However, <it>MhPR1</it>, <it>MhPR5 </it>and <it>MhPR8 </it>performed a distinct pattern of expression in different plant organs. <it>MhPR5 </it>and <it>MhPR8 </it>were basal expression in leaves, stems and roots, and <it>MhPR1 </it>was basal expression only in stems. The expression of <it>MhPR1</it>, <it>MhPR5 </it>and <it>MhPR8 </it>was enhanced during the first 48 h post-induced with SA, MeJA and ACC.</p> <p>Conclusions</p> <p>The results showed that a distinct pattern of expression of PR genes in <it>Malus hupehensis </it>which differed from the previous reports on model plants arabidopsis, tobacco and rice. <it>MhPR1</it>, <it>MhPR5 </it>and <it>MhPR8 </it>were induced by SA, MeJA and ACC, which were regarded as the marker genes in the SAR response in <it>Malus hupehensis</it>. In contrast with herbal plants, there could be specific signal pathway in response to SA, JA and ET for woody plants.</p

Interfacial Stabilization of a Graphene-Wrapped Cu2S Anode for High-Performance Sodium-Ion Batteries via Atomic Layer Deposition

Sodium-ion batteries (SIBs) have attracted increasing attention for storing renewable clean energy, owing to their cost-effectiveness. Nonetheless, SIBs still remain significant challenges in terms of the availability of suitable anode materials with high capacities and good rate capabilities. Our previous work has developed and verified that Cu2S wrapped by nitrogen-doped graphene (i.e., Cu2S@NG composite), as an anode in SIBs, could exhibit a superior performance with ultralong cyclability and excellent rate capability, mainly due to the multifunctional roles of NG. However, the Cu2S@NG anode still suffers from continuous parasitic reactions at low potentials, causing a rapid performance deterioration. In this study, we investigated the effects of a conformal Al2O3 coating via atomic layer deposition (ALD) on the interfacial stability of the Cu2S@NG anode. As a consequence, the ALD-coated Cu2S@NG electrode can deliver a high capacity of 374 mAh g&minus;1 at a current density of 100 mA g&minus;1 and achieve a capacity retention of ~100% at different rates. This work verified that surface modification via ALD is a viable route for improving SIBs&rsquo; performances

4D Printing of Soft Robotic Facial Muscles

4D printing is an emerging technology that prints 3D structures with smart materials that can respond to external stimuli and change shape over time. 4D printing represents a major manufacturing paradigm shift from single-function static structures to dynamic structures with highly integrated functionalities. Direct printing of dynamic structures can provide great benefits (e.g., design freedom, reduced weight, volume, and cost) to a wide variety of applications, such as sensors and actuators, and robotics. Soft robotics is a new direction of robotics in which hard and rigid components are replaced by soft and flexible materials to mimic actuation mechanisms in life, which are crucial for dealing with uncertain and dynamic tasks or environments. However, little research on direct printing of soft robotics has been reported. This paper presents a study on 4D printing of soft robotic facial muscles. Due to the short history of 4D printing, only a few smart materials have been successfully 4D printed, such as shape memory and thermo-responsive polymers, which have relatively small strains (~8%). In order to produce the large motion needed for facial muscles, dielectric elastomer actuators (DEAs), operating like a capacitor with a sheet of elastomer sandwiched by two compliant electrodes and known as artificial muscle for its high elastic energy density and capability of producing large strains (~200%) compared to other smart materials, is chosen as the actuator for our robotic facial muscles. In this paper, we report the first fully 4D printed soft robotic face using DEAs. A literature review on DEAs is first presented. In order to select the right material for our soft robotic face, the performance of different silicone-based candidate materials is tested and compared. A soft robotic face is then designed and fabricated using the selected material to achieve facial emotions by the motion of its lip and pupils actuated by the DEAs. This study demonstrates a 4D printed soft robotic face for the first time and the potential of 4D printing of soft robotics.Mechanical Engineerin

Comparative chemical diversity and antioxidant activities of three species of Akebia herbal medicines

Akebia stem has long been used extensively as a rare Chinese herbal medicine. The three most significant Akebia medicinal species are Akebia quinata (Thunb.) Decne. (A. quinata), Akebia trifoliata (Thunb.) Koidz. (A. trifoliata), and Akebia trifoliata (Thunb.) Koidz. var. Australis (Diels) Rehd. (A. trifoliata. var). They have significant therapeutic effects and are widely used in the pharmaceutical and cosmetics industries. Only a few studies compared their chemical differences and antioxidant activities. To better demonstrate each species' characteristics and antioxidant properties, the ultra-performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry (UPLC-Q-Orbitrap/MS)-based metabolomics was applied to investigate the chemome diversity of three Akebia species. Their antioxidant activities were evaluated by DPPH and ABTS assays. In total, 65 different metabolites were identified, including 5 phenolic acids, 2 phenylpropanoids, 4 lignan glycosides, and 54 triterpenoid saponins. The different aglycone types of triterpenoid saponins were found to be the component differences between the three Akebia species. The chemical composition of A. trifoliata and A. trifoliata. var is similar. The 2-(3,4-dihydroxyphenyl)-ethyl-O-β-d-glucopyranoside has been found only in A. quinata. In contrast, the triterpenoid saponins akemisaponin B, akemisaponin D, oleanolic-acid-3-O-arabinopyranosyl-28-O-glucopyranosyl-glucopyranosyl-rhamnopyranosyl-arabinopyranosyl, akemisaponin C and saponin Pj1 have been found A. trifoliata and A. trifoliata. var. As a result, these six compounds can be considered marker compounds that distinguish three Akebia species. The antioxidant activities results indicated that the antioxidants of three Akebia species were the same in different antioxidative test systems. A. trifoliata (IC50: 2.28–6.97 mg·mL−1) and A. trifoliata. var (IC50: 2.09–6.87 mg·mL−1) showed 2–3 times higher antioxidant activity than A. quinata (IC50: 5.56–11.21 mg·mL−1). This study reveals the antioxidant activity differences of three Akebia species, laying a foundation for further development and utilization. This type of study can lead to the identification of a compound that, with further work and more extensive studies, has the potential to be used as a biomarker, in this case to distinguish different medicinal species

In-plane self-assembly and lasing performance of cesium lead halide perovskite nanowires

Inorganic cesium lead halide perovskite nanowires (NWs) were synthesised by an in-plane self-assembly method. With the assistance of saturated solvent vapour, perovskite microparticles self-assembled into NWs. By stoichiometric adjustment of the halogen anion components in the NWs, their photoluminescence could be tuned to span the entire visible range. A detailed investigation of the lasing properties of the in-situ perovskite NWs and microplates revealed a lasing range of 420–560 nm, with typical thresholds of 18.8 μJ cm−2 for CsPbBr3 NWs and 8.87 μJ cm−2 for CsPbBrxCl3-x microplates. The NWs exhibited robust stability under extended laser pumping in ambient atmosphere