Multi‐Wavelength Light Drivable Oscillatory Actuator on Graphene‐Based Bilayer Film

A multi‐wavelength light drivable bilayer actuator is fabricated by depositing a thin layer of reduced graphene oxide (RGO) onto a flexible poly(dimethyl siloxane) (PDMS) substrate. The RGO/PDMS bilayer film shows fast and reversible bending/unbending motions upon exposure to UV light, visible light, or near‐infrared light (NIR). The photo‐thermal effect of the pump lights is studied by measuring and comparing the light induced temperature rises on RGO/PDMS film. The results demonstrate that the RGO absorbs and converts the light into heat. Thus the bilayer film undergoes thermal expansion under light irradiation. The calculated thermal expansion of the RGO thin layer is smaller than that of the PDMS layer, which results in the bilayer actuator bending towards the layer on the RGO side. Oscillational motion on the bilayer film is successfully achieved using continuous light irradiation on an offset sandwiched RGO/PDMS bilayer cantilever. Light induced motion on the RGO based film provides a new strategy for absorbing light energy and outputting photomechanical work.

     

Progress in the Field of Water‐ and/or Temperature‐Triggered Polymer Actuators

Water‐ and/or temperature‐triggered polymer actuators have great potential in robotics, microfabrication and micromanipulation, cell culture, artificial scaffolds, muscles, and motors. In the past few years, a large amount of work has been carried out, and several innovative concepts have been proposed to address challenges such as actuation with large‐scale displacement in a very short time, actuation of large‐sized samples, complex 3D shaping, directional control, multiresponsive actuation, and strong actuators. Herein, the progress made in the field of actuators triggered by water, temperature, and a combination of both is presented, emphasizing the new concepts of fast and direction‐controlled actuation, the corresponding mechanisms, the associated challenges, and future tasks and perspectives.     

Dual‐phase polymer electrolyte with enhanced mechanical strength

The effect of the heat treatment on the tensile properties and the dynamic moduli of polymer matrix films and polymer electrolytes were studied to further increase the mechanical properties. The crosslinking of latex particles brought about their improvements by heating. We have fabricated the polymer electrolyte with a tensile strength of 3.0 MPa, together with a conductivity above 1 mS/cm for application to a lithium secondary battery. This polymer electrolyte had the highest tensile strength among the known gel polymer electrolytes having conductivity over 1 mS/cm, although mechanical properties of plasticized polymer electrolytes have rarely been reported. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1835–1839, 1999     

N‐Cinnamoylation of Antimalarial Classics: Quinacrine Analogues with Decreased Toxicity and Dual‐Stage Activity

Plasmodium falciparum, the causative agent of the most lethal form of malaria, is becoming increasingly resistant to most available drugs. A convenient approach to combat parasite resistance is the development of analogues of classical antimalarial agents, appropriately modified in order to restore their relevance in antimalarial chemotherapy. Following this line of thought, the design, synthesis and in vitro evaluation of N‐cinnamoylated quinacrine surrogates, 9‐(N‐cinnamoylaminobutyl)‐amino‐6‐chloro‐2‐methoxyacridines, is reported. The compounds were found to be highly potent against both blood‐stage P. falciparum, chloroquine‐sensitive 3D7 (IC₅₀=17.0–39.0 nM ) and chloroquine‐resistant W2 and Dd2 strains (IC₅₀=3.2–41.2 and 27.1–131.0 nM , respectively), and liver‐stage P. berghei (IC₅₀=1.6–4.9 μM ) parasites. These findings bring new hope for the possible future “rise of a fallen angel” in antimalarial chemotherapy, with a potential resurgence of quinacrine‐related compounds as dual‐stage antimalarial leads.     

Simple and Rapid Fabrication of Large‐Scale Polymer‐Immobilized Colloidal Crystals by Spray Coating

Polymer‐immobilized colloidal crystal films have been fabricated by conventional spray coating and UV curing of silica–acrylic monomer suspensions. Controlling both the viscosity of the suspensions and the wettability of substrates enabled colloidal crystal films with smooth surfaces and brilliant structural colors due to Bragg diffraction. The structural colors could be controlled by particle concentrations in addition to particle diameter. The wettability influenced the thickness of the coated film and it consequently affected the Bragg reflection intensity of the film. Silhouette figures were textured on a substrate having regions with different wettabilities by single spray coating.

     

Rolling of 3D Printed Dual‐Layer Beam into a Cylinder by Ethanol Absorption

4D printing is an extension to 3D printing whereby a printed shape programmatically undergoes shape transformation through external stimulations. There is an increasing interest in this field because of its potential applications. However, many demonstrated shape transformations work on simple and limited geometrical shapes. In this work, the formation of a cylinder from a printed flat dual‐layer beam when exposed to ethanol is demonstrated. The newly formed cylinder retains its shape even when the ethanol is removed through the use of a locking mechanism. The proposed method can be used for building medical stents or various sensors and actuators that require cylindrical shapes.     

MXene-Based Soft Actuators with Multiresponse and Diverse Applications by a Simple Method

Smart actuators that can convert external energy stimuli into mechanical energy output have great potential in industrial, biomedical, and military applications. However, the existed disadvantage such as complex fabrication process, single stimulus source, and the requirement of artificial energy restrict their further development. Herein, a MXene/polyethylene (PE)-based soft actuator with multistimulus response and the ability to be driven by natural sunlight and human humidity is proposed through a simple method. Owing to the excellent electrical conductivity, high photothermal conversion capability, and surface hydrophilicity of MXene, the MXene/PE actuator exhibits rapid and large bending deformation in response to external multistimuli such as light, electricity, heat, and humidity. Owing to the simple preparation, and anisotropic, tailorable and programmable properties of the MXene/PE actuator, a soft robot that can crawl directionally under light conditions is constructed. In addition, based on the high sensitivity response of the actuator to light and humidity, smart clothing that can generate reversible bending deformation under natural sunlight as well as sweat conditions is developed. These results provide a new inspiration for the design of high-performance soft actuators with multistimulus response, and demonstrate the potential applications of the MXene/PE actuators in smart devices, bionic robots, and wearable clothing.     

Preparation and Reinforcement of Dual‐Porous Biocompatible Cellulose Scaffolds for Tissue Engineering

Biocompatible cellulose‐based aerogels composed of nanoporous struts, which embed interconnected voids of controlled micron‐size, have been prepared employing temporary templates of fused porogens, reinforcement by interpenetrating PMMA networks and supercritical carbon dioxide drying. Different combinations of cellulose solvent (Ca(SCN)₂/H₂O/LiCl or [EMIm][OAc]/DMSO) and anti‐solvent (EtOH), porogen type (paraffin wax or PMMA spheres) and porogen size (various fractions in the range of 100–500 μm) as well as intensity of PMMA reinforcement have been investigated to tailor the materials for cell scaffolding applications. All aerogels exhibited an open and dual porosity (micronporosity >100 μm and nanoporosity extending to the low micrometer range). Mechanical properties of the dual‐porous aerogels under compressive stress were considerably improved by introduction of interpenetrating PMMA networks. The effect of the reinforcing polymer on attachment, spreading, and proliferation of NIH 3T3 fibroblast cells, cultivated on selected dual‐porous aerogels to pre‐evaluate their biocompatibility was similarly positive.     

Human‐Iris‐Like Aperture and Sphincter Muscle Comprising Hyperelastic Composite Hydrogels Containing Graphene Oxide

Soft hydrogels are extensively studied for developing human‐body‐mimicking actuators because of their stimuli‐responsive volume change and elasticity. Mimicking a human eye with hydrogels is very challenging because both the large variation in the volume and the high modulus of the gels should be concurrently achieved. In the human eye, adjusting the iris for controlling the focal point and light transmittance is achieved by the contraction of the sphincter muscle. In this work, a hyperelastic poly(N‐isopropylacrylamide) containing graphene oxide (PNIPAm/GO) composite hydrogels, which exhibits a thermo‐responsive volume phase transition is developed. The fact that the inner hole size for center‐cut hydrogels can increase or decrease during heating depending on the geometry of the hydrogels is revealed. Based on these findings, human‐iris‐like actuators capable of controlling the shape of a polydimethylsiloxane (PDMS) lens for adjusting magnification of an object is developed. When heated, the hyperelastic hydrogels act like the sphincter muscle in the eye, inducing the curvature change of the attached PDMS lens. Thus, hyperelastic hydrogels of large variation can provide an efficient platform to fabricate various soft actuation systems.     

Chitosan–Quercetin Bioconjugate as Multi‐Functional Component of Antioxidants and Dual‐Responsive Hydrogel Networks

Multifunctional hydrogels based on chitosan–quercetin (CHITQ) conjugate are prepared by a thermo‐induced radical procedure in the presence of N‐isopropylacrylamide (NIPAAm), acrylamide (AAm), and N,N′‐methylenebis(acrylamide) (MEBA). At first, quercetin (Q) is grafted onto chitosan backbone with a functionalization degree of 275 mg of Q per gram of conjugate, as calculated by ¹H‐NMR analyses to impart antioxidant properties to the polysaccharide. Then, a pH and temperature sensitive hydrogel was obtained by involving CHITQ and NIPAAm in the polymerization reaction. The accessibility of phenolic moieties is modified in response to the hydrogel swelling/deswelling, as confirmed by antioxidant tests performed at different temperatures. Dual stimuli‐responsive hydrogels are proposed for the delivery of caffeine as model drug. The release profiles of caffeine depict a system particularly performing as on/off device at acidic pH with excellent applicability prospects.     

Graphene‐supported nickel ferrite: A magnetically separable photocatalyst with high activity under visible light

A straightforward strategy is designed for the fabrication of a magnetically separable NiFe₂O₄‐graphene photocatalyst with different graphene content. It is very interesting that the combination of NiFe₂O₄ nanoparticles with graphene sheets results in a dramatic conversion of the inert NiFe₂O₄ into a highly active catalyst for the degradation of methylene blue (MB) under visible light irradiation. The significant enhancement in photoactivity under visible light irradiation can be ascribed to the reduction of GO, because the photogenerated electrons of NiFe₂O₄ can transfer easily from the conduction band to the reduced GO, effectively preventing a direct recombination of electrons and holes. The results of the kinetic study indicated that the rate‐determining stage is the adsorption process of MB molecules. NiFe₂O₄ nanoparticles themselves have a strong magnetic property, which can be used for magnetic separation in a suspension system, and, therefore, the introduction of additional magnetic supports is no longer necessary. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Experimental and Numerical Investigations of a Dual‐Stage Cyclone Separator

Cyclone separators can be utilized in parallel to increase particle collection efficiency. However, this leads to a maldistribution problem that causes separation performance deterioration. To improve the flow distribution, a dual‐stage multicyclone separator (DSCS) was designed, containing a tangential‐inlet circle pathway cyclone array, an axial‐inlet radiation pathway cyclone array, and a cylindrical outer chamber. Experimental and computational fluid dynamics results revealed the gas‐particle flow distribution through multicyclone arrays. Effects of flow distribution on particle deposition were investigated experimentally. Particle trajectories inside the cyclone separators were also observed. The multicyclone array proved to generate a uniform inlet velocity distribution. The proposed cyclone separator can be considered as an option to accomplish dilute gas‐particle separation.     

Dual‐Curing of Waterborne Urethane‐Acrylate Coatings by UV and Thermal Processing

A waterbased dual‐cure urethane‐acrylate oligomer has been synthesized by polycondensation of monomers bearing hydroxyl, isocyanate and acrylate groups. To obtain a stable aqueous dispersion, carboxylate groups were grafted on the oligomer chain and the isocyanate groups were protected by a blocking agent. After water release by a brief heating, the dry films were cured either by a short UV exposure in the presence of a photoinitiator to induce the polymerization of the acrylate double bonds, or by heating up to 150 °C to release the isocyanates and promote the polycondensation by reaction with the hydroxyl groups, but mainly by a combination of UV and thermal cure. Both processes have been followed quantitatively by infrared spectroscopy to evaluate the influence of the temperature on the reaction rate and on the cure extent. The newly developed waterbased dual‐cure coatings were found to be quite resistant to accelerated weathering because of their aliphatic structure and their high crosslink density. Their light stability was substantially improved by the addition of a hydroxyphenyltriazine UV absorber and a hindered amine radical scavenger.

Thermal curing of the dual‐cure waterborne PUA formulation at a temperature of 150 °C.     

Fast Chemo‐Responsive Shape Memory of Stretchable Polymer Nanocomposite Aerogels Fabricated by One‐Step Method

A new type of stretchable poly(caprolactone)/graphene oxide (PCL/GO) aerogel with fast chemo‐responsive shape memory effect is fabricated by one‐step method of a sol‐gel procedure. The PCL/GO aerogels show uniformly circular and interconnected pores formed by twisted PCL nanolayers. GO platelets improve the crystallinity of PCL and increase the fracture stress and strain by 150% and 300% respectively, although the GO loading is only 0.5%. The dramatic increment of break strain is attributed to the uniform and circular pores that can afford large deformation and the interaction of GO and PCL. The aerogels can be programmed by external stress at ambient temperature without heating and recover upon ethyl acetate (EA) in 1 s. The fast chemo‐responsive shape recovery is ascribed to the fast wrinkle of the PCL nanolayers that decrease the diffusion time greatly and the interconnected micrometer pores that are in favor of penetrating for EA molecules.     

Dual‐bed catalyst system for the direct synthesis of high density aviation fuel with cyclopentanone from lignocellulose

In this article, we demonstrated an integrated process for the direct production of tri(cyclopentane) with cyclopentanone which can be obtained from lignocellulose. The reaction was carried out in a dual‐bed continuous flow reactor. In the first bed, cyclopentanone was selectively converted to 2,5‐dicyclopentylcyclopentanol over the Pd‐MgAl‐HT (hydrotalcite) catalyst. Under solvent‐free and mild conditions (443 K, 0.1 MPa H₂), high carbon yield (81.2%) of 2,5‐dicyclopentylcyclopentanol was achieved. Subsequently, the 2,5‐dicyclopentylcyclopentanol was further hydrodeoxygenated to tri(cyclopentane) in the second bed. Among the investigated catalysts, the Ni‐Hβ‐DP prepared by deposition‐precipitation (DP) method exhibited the highest activity for the hydrodeoxygenation step. By using Pd‐MgAl‐HT as the first bed catalyst and Ni‐Hβ‐DP as the second bed catalyst, tri(cyclopentane) was directly produced at high carbon yield (80.0%) with cyclopentanone as feedstock. This polycycloalkane has high density (0.91 kg/L) and can be used as additive to improve the density and volumetric heating value of bio‐jet fuel. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2754–2761, 2016     

Polyimide/Graphene Nanocomposites with Improved Gas Barrier and Thermal Properties due to a “Dual‐Plane” Structure Effect

Graphene nanosheets are prepared by solution‐phase exfoliation of graphite and successfully incorporated with polyimide to obtain polyimide/graphene (DABPI/G) nanocomposites via in situ polymerization. Compared with those of pure DABPI, the DABPI/G nanocomposites exhibit better barrier and thermal properties. The oxygen and water vapor transmission rates of the DABPI/G (0.5 wt%) nanocomposite are 0.69 cm³ m^?2 d^?1 and 0.44 g m^?2 d^?1, respectively, which are 92 and 85% lower than those of pure DABPI. Meanwhile, the DABPI/G (0.5 wt%) nanocomposite exhibits excellent thermal stability with a T_d5% of 578 °C and a coefficient of thermal expansion of ?0.19 ppm K^?1. The excellent barrier and thermal properties of DABPI/G nanocomposites are mainly attributed to the fine dispersion and orientation of the graphene nanosheets, increased crystallinity, and low free volume of the DABPI matrix. These are the result of the “dual‐plane” structure effect, which is the synergistic orientation effect between the rigid planar molecular chains of DABPI and the nanosheets of graphene.     

Mechanical and piezo‐resistive properties of styrene–butadiene–styrene copolymer covalently modified with graphene/styrene–butadiene–styrene composites

As novel piezoelectric materials, carbon‐reinforced polymer composites exhibit excellent piezoelectric properties and flexibility. In this study, we used a styrene–butadiene–styrene triblock copolymer covalently grafted with graphene (SBS‐g‐RGO) to prepare SBS‐g‐RGO/styrene–butadiene–styrene (SBS) composites to enhance the organic solubility of graphene sheets and its dispersion in composites. Once exfoliated from natural graphite, graphene oxide was chemically modified with 1,6‐hexanediamine to functionalize with amino groups (GO–NH₂), and this was followed by reduction with hydrazine [amine‐functionalized graphene oxide (RGO–NH₂)]. SBS‐g‐RGO was finally obtained by the reaction of RGO–NH₂ and maleic anhydride grafted SBS. After that, X‐ray diffraction, X‐ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and other methods were applied to characterize SBS‐g‐RGO. The results indicate that the SBS molecules were grafted onto the graphene sheets by covalent bonds, and SBS‐g‐RGO was dispersed well. In addition, the mechanical and electrical conductivity properties of the SBS‐g‐RGO/SBS composites showed significant improvements because of the excellent interfacial interactions and homogeneous dispersion of SBS‐g‐RGO in SBS. Moreover, the composites exhibited remarkable piezo resistivity under vertical compression and great repeatability after 10 compression cycles; thus, the composites have the potential to be applied in sensor production. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46568.     

Targeting the Erythrocytic and Liver Stages of Malaria Parasites with s‐Triazine‐Based Hybrids

A diversity‐oriented library of s‐triazine‐based hybrids was screened for activity against the chloroquine‐resistant Plasmodium falciparum W2 strain. The most striking result was sub‐micromolar activity against cultured erythrocytic‐stage parasites of hybrid molecules containing one or two 8‐aminoquinoline moieties. These compounds were not clearly toxic to human cells. The most effective blood‐schizontocidal s‐triazine derivatives were then screened for activity against the liver stage of malaria parasites. The s‐triazine hybrid containing two 8‐aminoquinoline moieties and one chlorine atom emerged as the most potent against P. berghei liver‐stage infection, active in the low nanomolar region, combined with good metabolic stability in rat liver microsomes. These results indicate that s‐triazine‐8‐aminoquinoline‐based hybrids are excellent starting points for lead optimization as dual‐stage antimalarials.