Dielectric elastomers are of interest for actuator applications due to their large actuation strain, high bandwidth, high energy density, and their flexible nature. If future dielectric elastomers ...are to be used reliably in applications that include soft robotics, medical devices, artificial muscles, and electronic skins, there is a need to design devices that are tolerant to electrical and mechanical damage. In this paper, the first report of self‐healing of both electrical breakdown and mechanical damage in dielectric actuators using a thermoplastic methyl thioglycolate–modified styrene–butadiene–styrene (MGSBS) elastomer is provided. The self‐healing functions are examined from the material to device level by detailed examination of the healing process, and characterization of electrical properties and actuator response before and after healing. It is demonstrated that after dielectric breakdown, the initial dielectric strength can be recovered by up to 67%, and after mechanical damage, a 39% recovery can be achieved with no degradation of the strain–voltage response of the actuators. The elastomer can also heal a combination of mechanical and electrical failures. This work provides a route to create robust and damage tolerant dielectric elastomers for soft robotic and other applications related to actuator and energy‐harvesting systems.
This is the first report of self‐healing of both electrical breakdown and mechanical damage in dielectric actuators using a thermoplastic methyl thioglycolate–modified styrene–butadiene–styrene (MGSBS) elastomer. After dielectric breakdown, the dielectric strength can be recovered by up to 67%, and after mechanical damage, a 39% recovery can be achieved with no degradation of the strain–voltage response of the actuators.
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•Review working mechanism and modification strategies of plasma-treatment of CNPs.•In comparison with other covalent surface functionalisation methods.•Amino- and ...plasma-functionalised carbon nanoparticles for epoxy resins.
Composites of polymers and nanoparticles continue to find increasing applications from biomedical to electronics to transport systems. Nanostructured carbon nanoparticles (CNPs) having geometries from 0D to 3D are important functional additives for polymers, having great potential to produce composite materials with a range of enhanced properties including mechanical, optical, electrical and thermal. However, these possibilities have not been fully realised due to the difficulties associated with CNP dispersion in and their interaction with polymer matrices across the length scales. The surfaces of CNPs are intrinsically chemically inert and hydrophobic, and they tend to form agglomerates or bundles. Therefore, surface functionalisation of CNPs becomes a critical pre-requisite in the fabrication of polymer nanocomposites. Various functionalisation methods have been developed including, chemical, mechanochemical, electrochemical, and irritation reactions in order to activate the carbon surface, which subsequently interact with polymers through covalent bonding or non-covalent interactions. Wet-chemistry methods consume large amounts of organic solvents, hazardous chemicals, require multi-step purification with typically low yields. Mechanochemistry techniques such as ball milling can produce edge-functionalised CNPs at the expense of reduced aspect ratio. In contrast, cold plasma treatment offers a simple, clean, solvent-free, and scalable technique for modifying CNPs with variable functional groups. Recent developments in plasma-treated CNPs have driven its applications extensively in epoxy-based composites. Amino-functionalisation of CNPs is particularly favourable, as the amine group offers a rich reaction platform to enhance the activity of the CNP as both modifier and crosslinker for epoxy resins. Research activity in this area is under development but growing rapidly. In this review, we introduce the working mechanism for plasma functionalisation of CNPs, and compare this approach with the efficiency and effectiveness of wet-chemistry methods. The discussion will focus on amine-functionalised CNPs (carbon nanotubes, graphene/graphene oxide and carbon fibre) and their use in the modification of the properties of epoxy resins.
Surface impurities such as water and surfactants can significantly affect the properties of 2D materials. They disrupt the 2D material lattice structure and surface chemistry and also promote ...electron and phonon scattering. Strategies to clean the surfaces of 2D materials are therefore critical to achieving optimal properties. Boron nitride nanosheets (BNNS) and exfoliated graphite nanoplatelets (GNP) are treated using three procedures: washing with ethanol, water‐assisted freeze‐drying, and freeze‐drying without addition of water in an attempt to remove two impurities—water and an ionic surfactant (sodium cholate, SC). There is total removal of water from BNNS when the starting material is treated using either freeze drying method whereas some water (≈40%) and traces of ethanol are detected in BNNS when washed with ethanol. It is not possible to exclude the presence of SC on BNNS and GNP post treatment; however, the relatively high amount of sodium (from SC) in the samples after freeze‐drying suggests the process contributed to the separation of BNNS and GNP aggregates. The BNNS flakes separate when washed with ethanol or freeze‐dried in the absence of water. The crystalline structure of BNNS and GNP is retained post treatments. This approach provides a route to cleaning and separating 2D materials.
Boron nitride nanosheets (BNNS) and exfoliated graphite nanoplatelets (GNP) are treated by washing with ethanol and freeze‐drying, in an attempt to remove traces of water and the surfactant sodium cholate (SC). The lattice structure of GNP and BNNS is unaffected and the removal of water and/or sodium cholate enhanced the thermal stability of the BNNS and GNP under oxidative conditions.
Understanding the properties of polymer carbon nanotube (CNT) composites is the key to these materials finding new applications in a wide range of industries, including but not limited to ...electronics, aerospace and biomedical/bioengineering. This book provides in-depth coverage of the preparation, characterization, properties and applications of these technologically interesting new materials. Part One covers the preparation and processing of composites of thermoplastics with CNTs, with chapters covering in-situ polymerization, melt processing and CNT surface treatment, as well as elastomer and thermoset CNT composites. Part Two concentrates on properties and characterization, including chapters on the quantification of CNT dispersion using microscopy techniques. In Part Three, the applications of polymer/CNT composites are reviewed, with chapters on specific applications such as in fibers and cables, bioengineering applications and conductive polymer CNT composites for sensing. This book is an essential reference for scientists, engineers and designers in high-tech industries and academia with an interest in polymer nanotechnology and nanocomposites.
Composites of poly(methyl methacrylate) (PMMA) with multi-walled carbon nanotubes (MWCNT) of varying aspect ratio and carboxylic acid functionality were prepared using melt mixing. The extent of ...dispersion and distribution of the MWCNTs in the PMMA matrix was investigated using a combination of high-resolution transmission electron microscopy (HRTEM), wide-angle X-ray diffraction (XRD) and Raman spectroscopy. The electrical resistivity and oscillatory shear rheological properties of the composites were measured as a function of MWCNT geometry, functionality, and concentration. The fundamental ballistic conductance of the pristine free-standing MWCNTs was investigated using a mechanically controlled break-junction method. The electrical conductivity of PMMA was enhanced by up to 11 orders of magnitude for MWCNT concentrations below 0.5
wt.%. MWCNTs having higher aspect ratio, above 500, or functionalized with carboxylic acid groups readily formed rheological percolated networks with thresholds, determined from a power law relationship, of 1.52 and 2.06
wt.%, respectively. The onset of pseudo-solid-like behaviour and network formation is observed as
G′,
η∗, and tan
δ
−1 are independent of frequency as MWCNT loading increased. Sufficiently long and/or functionalized tubes are required to physically bridge or provide interfacial interactions with PMMA to alter polymer chain dynamics. Carboxylic acid functionalization disrupts the crystalline order of MWCNTs due to a loss of π-conjugation and electron de-localisation of sp
2 C–C bonds resulting in non-ballistic electron transport in these tubes, irrespective of how highly dispersed they are in the PMMA matrix.
Cellulose nanocrystals (CNCs) and/or sepiolite (SPT) were thermomechanically mixed with un-plasticised chitosan and chitosan/carboxymethyl cellulose (CMC) blends plasticised with ...1-ethyl-3-methylimidazolium acetate (C
mimOAc). Examination of the morphology of these materials indicates that SPT aggregates were reduced when CNCs or C
mimOAc were present. Inclusion of CNCs and/or SPT had a greater effect on material properties when the matrices were un-plasticised. Addition of SPT or CNCs altered the crystalline structure of the un-plasticised chitosan matrix. Moreover, a combination of SPT and CNCs was more effective at suppressing re-crystallisation. Nonetheless, the mechanical properties and surface hydrophobicity were more related to CNC/SPT-biopolymer interactions. The un-plasticised bionanocomposites generally showed increased relaxation temperatures, enhanced tensile strength, and reduced surface wettability. For the C
mimOAc plasticised matrices, the ionic liquid (IL) dominates the interactions with the biopolymers such that the effect of the nanofillers is diminished. However, for the C
mimOAc plasticised chitosan/CMC matrix, CNCs and SPT acted synergistically suppressing re-crystallisation but resulting in increased tensile strength.
The excellent forecasts made by ECMWF predicting the devastating landfall of Hurricane Sandy attracted a great deal of publicity and praise in the immediate aftermath of the event. The almost ...unprecedented and sudden left hook of the storm toward the coast of New Jersey was attributed to interactions with the large-scale atmospheric flow. This led to speculation that satellite observations may play an important role in the successful forecasting of this event. To investigate the role of satellite data a number of experiments have been performed at ECMWF where different satellite observations are deliberately withheld and forecasts of the hurricane rerun. Without observations from geostationary satellites the correct landfall of the storm is still reasonably well predicted albeit with a slight timing shift compared to the control forecast. On the other hand, without polar-orbiting satellites (which represent 90% of the volume of currently ingested observations) the ECMWF system would have given no useful guidance 4-5 days ahead that the storm would make landfall on the New Jersey coast. Instead the hurricane is predicted to stay well offshore in the Atlantic and hit the Maine coast 24 h later. If background errors estimated from the ECMWF Ensemble of Data Assimilations (EDA) are allowed to evolve and adapt to the depleted observing system, then some of the performance loss suffered by withholding polar satellite data can be recovered. The use of the appropriate EDA errors results in a more enhanced use of geostationary satellite observations, which partly compensates for the loss of polar satellite data.
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