Silicone‐modified graphene oxide fillers via the Piers‐Rubinsztajn reaction

While graphene or graphene oxide can make significant improvements in the properties of a wide variety of polymeric materials, their incorporation can be challenged by incompatibility with the polymeric matrix. The modification of graphene oxide with silicones or silanes using the Piers‐Rubinsztajn reaction improves dispersibility in nonpolar materials, including organic solvents and silicone pre‐elastomers. A high loading (up to 10 wt %) of modified graphene oxide in silicone elastomers could be achieved, which resulted in enhanced mechanical performance and reduced gas permeability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2379–2385     

Thermoplastic Dielectric Elastomer of Triblock Copolymer with High Electromechanical Performance

Dielectric elastomer (DE) actuators have been shown to have promising applications as soft electromechanical transducers in many emerging technologies. The DE actuators, which are capable of large actuation strain over a wide range of excitation frequencies, are highly desirable. Here, the first single‐component DE of a triblock copolymer with attractive electromechanical performance is reported. Symmetric poly(styrene‐b‐butyl acrylate‐b‐styrene) (SBAS) is designed and synthesized. The SBAS actuator exhibits about 100% static actuation area strain and excellent dynamic performance, as evidenced by a wide half bandwidth of 300 Hz and a very high specific power of 1.2 W g^–1 within the excitation frequency range of 300–800 Hz.     

Optical Mechanotransduction with Carbazole‐Based Luminescent Liquid Single‐Crystal Elastomers

Carbazole‐based liquid single‐crystal elastomers (LSCEs) are valuable fluorescent flexible materials to perform optical mechanotransduction under ambient conditions. Indeed, the covalent incorporation of carbazole derivatives into nematic LSCEs allows to tune their luminescence on demand under mechanical control in a quick and reversible fashion. Specifically, the fluorescence intensity for these materials can be switched back and forth in less than a second. Moreover, such a process can be performed several times without detecting any sign of fatigue in the system. In addition, these materials show excellent resistance to aging; 2 years after their preparation they exhibit the very same mechanofluorescent behavior as when freshly prepared. In fact, the here reported fluorescent systems are highly sensitive; the application of a force of 70 mN decreases the fluorescence in the elastomeric material by 7%. Thus, mechanical forces are attractive external stimuli to modulate the fluorescence of nematic elastomers rapidly and reversibly enabling thereby mechanotransduction.

     

Capacitive Sensing of Amino Acids Using Caliraxene‐Coated Silicon Transducers

The possibility of using capacitance and flat band voltage as measurable quantities for determining amino acids that are neither electroactive nor with strong UV‐vis absorption has been explored. The sensors were fabricated by immobilizing calixarene derivatives on Si/SiO₂/Si₃N₄ transducers. The measurements were made in sulfuric acid media of ca. pH 1 and in physiological buffer of pH 7.4. The different calixarene derivatives showed varying sensitivities to the amino acids ranging from 8 to 137 mV/decade.     

微结构化弹性体介电层的制备方法与应用

微结构化弹性体薄膜是指在表面或内部具有多孔或者特殊造型阵列的微纳米尺寸结构的弹性体薄膜,这类薄膜作为功能化介电层在柔性电子器件的制备领域获得了广泛的应用.本文从微结构弹性体介电层的制备和应用两个方面来介绍微结构弹性体介电层的研究进展,首先介绍了可用以制备介电层的弹性体的种类,然后综述了多孔和非多孔阵列两大类微结构弹性体...     

A New Way to Silicone‐Based Peptide Polymers

We describe a new class of silicone‐containing peptide polymers obtained by a straightforward polymerization in water using tailored chlorodimethylsilyl peptide blocks as monomeric units. This general strategy is applicable to any type of peptide sequences, yielding linear or branched polymer chains composed of well‐defined peptide sequences.     

Dielectric Relaxation and Beyond Limiting Behavior of Alternating‐Current Conductivity in a Supermolecular Ferroelectric

A cyclen‐based hybrid supermolecule crystal, [(FeCl₂)(cyclen)]Cl ( 1 ), where cyclen=1,4,7,10‐tetraazacyclododecane, was prepared using a liquid–liquid diffusion approach. The variable crystal structures exhibit that compound 1 belongs to an orthorhombic crystal system, Pna2₁ space group (point group C_2V) in the temperature range of 150–400 K. This hybrid supermolecule shows a dielectric relaxation behavior around room temperature, and the ferroelectric nature of 1 has been directly verified by hysteresis measurements. In addition, the AC (alternating current) conductivity study reveals that the 1 displays a beyond limiting behavior. These interesting findings are for the first time reported in the field of supermolecular ferroelectrics. This study may open a new way to construct supermolecular ferroelectrics and give insights into their conductor behavior.     

Lead Sensor Using Gold Nanostructured Screen‐Printed Carbon Electrodes as Transducers

Gold nanostructured screen‐printed carbon electrodes are demonstrated to be suitable transducers for the determination of lead using square‐wave voltammetry. Reproducible gold nanostructures have been obtained by direct electrochemical deposition. A calibration plot from 2.5 to 250 μg/L was obtained in acidic solutions of Pb(II) with a reproducibility of 4% (n=10). The detection limit was 0.09 μg/L of lead. The method is then applied to perform a blood lead analysis by adjusting square‐wave parameters in capillary or venous blood with a minimum sample pretreatment and excellent accuracy and reproducibility.     

Electroactive Polymers: Developments of and Perspectives for Dielectric Elastomers

We present the development and applications of dielectric elastomers. For the last 10 years the significance of this class of polymers has risen as more applications seem possible and first products have been commercialized.     

Room‐Temperature,Strain‐Tunable Orientation of Magnetization in a Hybrid Ferromagnetic Co Nanorod–Liquid Crystalline Elastomer Nanocomposite

Hybrid nanocomposites based on magnetic nanoparticles dispersed in liquid crystalline elastomers are fascinating emerging materials. Their expected strong magneto‐elastic coupling may open new applications as actuators, magnetic switches, and for reversible storage of magnetic information. We report here the synthesis of a novel hybrid ferromagnetic liquid crystalline elastomer. In this material, highly anisotropic Co nanorods are aligned through a cross‐linking process performed in the presence of an external magnetic field. We obtain a highly anisotropic magnetic material which exhibits remarkable magneto‐elastic coupling. The nanorod alignment can be switched at will at room temperature by weak mechanical stress, leading to a change of more than 50 % of the remnant magnetization ratio and of the coercive field.     

Silicone‐based impact modifiers for poly(vinyl chloride), engineering resins,and blends

Silicone‐based impact modifiers were prepared in a previous study. The modifiers were composed of silicone/acrylic rubber cores and grafted acrylic shells. They improved the toughness of poly(vinyl chloride) (PVC) and poly(methyl methacrylate). The silicone emulsion that was used to produce the silicone‐based impact modifiers was prepared via two routes: emulsion polymerization and bulk polymerization of octamethyltetracyclosiloxane. Many silicone‐based impact modifiers were produced that had different silicone/acrylic rubber characteristics. Through a toughness examination of modified PVC, the best composition of the silicone‐based impact modifiers was obtained, and the silicone content in the rubber composition was 25 wt %. The morphology of the silicone‐based impact modifiers, determined by transmission electron microscopy, was as follows: core and second shell polymers were mainly poly(butyl acrylate), and the first shell polymer was silicone. The silicone‐based impact modifiers were blended with engineering resins such as PVC, polycarbonate (PC), poly(butylene terephthalate) (PBT), and PC/PBT mixtures. The impact strength under standard conditions and after weathering test conditions for blends of the silicone‐based impact modifiers were investigated with respect to two commercially available acrylic and methyl methacrylate/butadiene/styrene impact modifiers. The results showed good weatherability and good toughness under low‐temperature conditions for the silicone‐based impact modifiers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1112–1119, 2004     

A Novel and Non‐Cytotoxic Self‐Healing Supramolecular Elastomer Synthesized with Small Molecular Biological Acids

A novel and non‐cytotoxic self‐healing supramolecular elastomer (SE) is synthesized with small‐molecular biological acids by hydrogen‐bonding interactions. The synthesized SEs behave as rubber at room temperature without additional plasticizers or crosslinkers, which is attributed to the phase‐separated structure. The SE material exhibits outstanding self‐healing capability at room temperature and essential non‐cytotoxicity, which makes it a potential candidate for biomedical applications.

     

Molecular Dynamics,Phase Transition and Frequency‐Tuned Dielectric Switch of an Ionic Co‐Crystal

Dielectric switches that can be converted between high and low dielectric states by thermal stimuli have attracted much interest owing to their many potential applications. Currently one main drawback for practical application lies in the non‐tunability of their switch temperatures (T_S). We report here an ionic co‐crystal (Me₃NH)₄[Ni(NCS)₆] that contains a multiply rotatable Me₃NH⁺ ion and a solely rotatable one due to a more spacious supramolecular cage for the former one. This compound undergoes an isostructural order–disorder phase transition and it can function as a frequency‐tuned dielectric switch with highly adjustable T_S, which is further revealed by the variable‐temperature structure analyses and molecular dynamics simulations. In addition, the distinct arrangements and molecular dynamics of two coexisting Me₃NH⁺ ions confined in different lattice spaces as well as the notable offset effect on the promoting/hindering of dipolar reorientation after dielectric transition provide a rarely observed but fairly good model for understanding and modulating the dipole motion in crystalline environment.     

Dielectric Properties of Polyimide‐Mica Hybrid Films

Summary: Polyimide‐mica hybrid films were prepared via ultrasonic dispersion and in situ polymerization process from a solution of a polyimide precursor and mica in N,N‐dimethylacetamide, and their structure was characterized by FTIR and XRD techniques. The dependence of dielectric properties, such as dielectric constant and electrical breakdown strength, of the hybrid films on the content of mica was studied at room and cryogenic temperatures. The results show that the dielectric constant of PI‐mica hybrid films decreases with the increase of the mica content at temperatures from −150 to 150 °C and at frequency range from 1 kHz to 1 MHz. It was found that the cryogenic electrical breakdown strength of the PI‐mica hybrid films could meet the requirements of cryogenic insulating materials.

Effect of frequency on the dielectric constant of PI‐mica hybrid films at 140 °C at the frequency from 1 kHz to 1 MHz.     

Nematic Liquid Crystalline Elastomer Grating and Microwire Fabricated by Micro‐Molding in Capillaries

A new approach is developed to fabricate highly oriented mono‐domain LCE nano/microstructures through micro‐molding in capillaries. Gratings and microwires as two typical examples are fabricated and characterized by polarizing optical microscopy, optical microscopy, and scanning electron microscopy. The gratings with precisely controlled sizes and smooth surface are obtained by filling the channels with a nematic monomer mixture followed by the photo‐crosslinking. After peeling off the gratings from the substrate, the free‐standing microwires are obtained. A uniform orientation of the mesogenic units is observed for the molds with channel width less than 20 μm. Reversible thermomechanical effect is demonstrated by using the microwires obtained through this approach.     

Enhanced dielectric performance of a block copolymer‐polythiophene nanocomposite

Dielectric elastomer actuators (DEAs) transform electrical energy into mechanical work. However, despite displaying exceptional features, the low permittivity of elastomers restricts their application. Hence, to overcome this limitation, DEAs are fabricated by dispersing poly(3‐methylthiophene acetate) (P3TMA), a polarizable conducting polymer, into poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS), a thermoplastic elastomer with excellent mechanical properties. Although high‐quality SEBS:P3TMA films are obtained for all compositions (between 0.5 and 20 wt % P3TMA), their thickness and surface roughness increase with the nano‐sized filler content. Moreover, the conducting particles are well integrated into the SEBS network with no evidence of aggregation or significant change in the mechanical properties of the composites. P3TMA, which forms encapsulated conductive domains within the polymeric matrix, improves the dielectric behavior of SEBS:P3TMA by increasing their dielectric constant with low dielectric losses and no current leakage. Thus, indicating the potential future application of these nanocomposites as elastomer actuators or high energy density capacitors. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1896–1905     

A New Type of Macroscopically Oriented Smectic‐A Liquid Crystal Elastomer

Smectic‐A liquid single crystal elastomers (S_A‐LSCE) are materials where the rubber elasticity of the polymer network is combined with the one‐dimensional positional long‐range order of mesogenic groups which are covalently attached to the network. In the systems investigated so far, a mechanical deformation of the network causes significant reorientation processes of the layered structure. We present a new type of S_A‐LSCE in which this structure remains unaffected on mechanical deformation both parallel and perpendicular to the director. The thermoelastic behavior, macroscopic dimensions, and stress–strain measurements parallel as well as perpendicular to the director are investigated. X‐ray studies confirm that a deformation parallel and perpendicular to the layer normal does not alter the macroscopically ordered lamellar structure with respect to the order parameter and the layer correlation length. We propose a simple picture where defects within the lamellar structure might account for these findings.

     

Dielectric and thermal characterization of low density ethylene/10‐undecen‐1‐ol copolymers prepared with nickel catalysts

Ethylene and 10‐undecen‐1‐ol copolymers, prepared using a nickel complex as catalyst, were studied using differential scanning calorimetry (DSC), X‐ray diffraction, and dielectric relaxation spectroscopy. The behavior exhibited by copolymers containing incorporated 10‐undecen‐1‐ol amounts within 0.5 and 4.6 mol % was compared with neat polyethylene. DSC revealed that a new crystalline region with lower thickness lamellae emerges in copolymers due to the side‐chains crystallization. Nevertheless, the global crystallization degree decreases due to the loss of crystallinity that occurs in a greater extent in PE‐like regions. Dielectric relaxation spectroscopy detected two processes, a low activation energy process below ?20 °C related with localized mobility increasing in intensity and deviating to higher temperatures with the increase in 10‐undecen‐1‐ol amount, and a high activation energy process ascribed to the glass transition, located at higher temperatures for the different copolymers relatively to neat polyethylene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2802–2812, 2007     

Silicon‐Based Dielectric Metamaterials: Focus on the Current Synthetic Challenges

Metamaterials have optical properties that are unprecedented in nature. They have opened new horizons in light manipulation, with the ability to bend, focus, completely reflect, transmit, or absorb an incident wave front. Optically active metamaterials in particular could be used for applications ranging from 3D information storage to photovoltaic cells. Silicon (Si) particles are some of the most promising building blocks for optically active metamaterials, with high scattering efficiency coupled to low light absorption for visible frequencies. However, to date ideal Si building blocks cannot be produced by bulk synthesis techniques. The key is to find a synthetic route to produce Si building blocks between 75–200 nm in diameter of uniform size and shape, that are crystalline, have few impurities, and little to no porosity. This Review provides a theoretical background on Si optical properties for metamaterials, an overview of current synthetic methods and gives direction towards the most promising routes to ideal Si particles for metamaterials.     

Amphiphilic thermoset elastomers from metal‐free,click crosslinking of PEG‐grafted silicone surfactants

The hydrophobicity of silicone elastomers can compromise their utility in some biomaterials applications. Few effective processes exist to introduce hydrophilic groups onto a polysiloxane backbone and subsequently crosslink the material into elastomers. This problem can be overcome through the utilization of metal‐free click reactions between azidoalkylsilicones and alkynyl‐modified silicones and/or PEGs to both functionalize and crosslink silicone elastomers. Alkynyl‐functional PEG was clicked onto a fraction of the available azido groups of a functional polysiloxane, yielding azido reactive PDMS‐g‐PEG rake surfactants. The reactive polymers were then used to crosslink alkynyl‐terminated PDMS of different molecular weights. Using simple starting materials, this generic yet versatile method permits the preparation and characterization of a library of amphiphilic thermoset elastomers that vary in their composition, crosslink density, elasticity, hydrogel formation, and wettability. An appropriate balance of PEG length and crosslink density leads to a permanently highly wettable silicone elastomer that demonstrated very low levels of protein adsorption. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1082–1093