Structure and dielectric properties of electroactive tetraaniline grafted non-polar elastomers

Intrinsic modification of polybutadiene and block copolymer styrene–butadiene–styrene with the electrically conducting emeraldine salt of tetraaniline (TANI) via a three-step grafting method, is reported in this work. Whilst the TANI oligomer grafted at a similar rate to both polybutadiene and styrene–butadiene–styrene under the same conditions, the resulting elastomers exhibited vastly different properties. 1 mol% TANI-PB exhibited an increased relative permittivity of 5.9, and a high strain at break of 156%, whilst 25 mol% TANI-SBS demonstrated a relative permittivity of 6.2 and a strain at break of 186%. The difference in the behaviour of the two polymers was due to the compatibilisation of TANI by styrene in SBS through π-π stacking, which prevented the formation of a conducting TANI network in SBS at. Without the styrene group, TANI-PB formed a phase separated structure with high levels of TANI grafting. Overall, it was concluded that the polymer chain structure, the morphology of the modified elastomers, and the degree of grafting of TANI, had the greatest effect on the mechanical and dielectric properties of the resultant elastomers. This work paves the way for an alternative approach to the extrinsic incorporation of conducting groups into unsaturated elastomers, and demonstrates dielectric elastomers with enhanced electrical properties for use in actuation devices and energy harvesting applications

Polymerisable surfactants for polymethacrylates using catalytic chain transfer polymerisation (CCTP) combined with sulfur free-RAFT in emulsion polymerisation

Statistical copolymers of methacrylic acid and methyl methacrylate were synthesised via free radical catalytic chain transfer polymerisation (CCTP) in emulsion to form a hydrophilic emulsifier/surfactant. The vinyl-terminated oligomers were in turn utilised as chain transfer agents, with no further purification, for the formation of diblock copolymers with butyl and methyl methacrylate which constitutes the emulsifier via sulfur-free reversible addition–fragmentation chain transfer polymerisation (SF-RAFT). In turn these polymers were solubilized with various concentrations of ammonium hydroxide and utilised in the surfactant-free emulsion polymerization of butyl methacrylate using persulfate initiators, which also stabilized the polymer particles with observed no coagulation, with solid contents as high as 40%

Challenges and Opportunities of Self-healing Polymers and Devices for Extreme and Hostile Environments

Engineering materials and devices can be damaged during their service life as a result of mechanical fatigue, punctures, electrical breakdown, and electrochemical corrosion. This damage can lead to unexpected failure during operation, which requires regular inspection, repair, and replacement of the products, resulting in additional energy consumption and cost. During operation in challenging, extreme, or harsh environments, such as those encountered in high or low temperature, nuclear, offshore, space, and deep mining environments, the robustness and stability of materials and devices are extremely important. Over recent decades, significant effort has been invested into improving the robustness and stability of materials through either structural design, the introduction of new chemistry, or improved manufacturing processes. Inspired by natural systems, the creation of self-healing materials has the potential to overcome these challenges and provide a route to achieve dynamic repair during service. Current research on self-healing polymers remains in its infancy, and self-healing behavior under harsh and extreme conditions is a particularly untapped area of research. Here, the self-healing mechanisms and performance of materials under a variety of harsh environments are discussed. An overview of polymer-based devices developed for a range of challenging environments is provided, along with areas for future research

Aqueous copper-mediated reversible deactivation radical polymerization (RDRP) utilizing polyetheramine derived initiators

Copper-mediated reversible deactivation radical polymeriation (Cu-RDRP) in aqueous media has been employed to synthesize temperature-responsive block copolymers, utilizing both hydrophobic and hydrophilic amide functional macroinitiators derived from polyetheramines (Jeffamines™). The in situ and rapid diproportionation of Cu(I)Br/Me6TREN in water is exploited for the efficient homopolymerization of N-isopropyl acrylamide (NIPAM) and dimethyl acrylamide (DMA), at near full conversions (>99%), with low dispersity (Đ < 1.18) and with a range of molar masses. The Jeffamine™-derived macroinitiators were used for both the synthesis of homopolymer and for one-pot chain extensions and block copolymerizations (i.e. Jeffamine™-PNIPAM-b-PDMA). The obtained polymers exhibit controlled thermoresponsive aggregation behaviour which varies depending on the hydrophilicity/hydrophobicity of the macroinitiators and the composition of the block copolymers. Thermal analysis and dynamic light scattering (DLS) give an insight into the effect of these macroinitiators on the thermoresponsive aggregation behaviour of the synthesized polymers

A simple and versatile route to amphiphilic polymethacrylates : catalytic chain transfer polymerisation (CCTP) coupled with post-polymerisation modifications

Amphiphilic polymers have become key figures in the fields of pharmacology, medicine, agriculture and cosmetics. The use of reversible deactivation radical polymerisation (RDRP) techniques has allowed advances in the synthesis of amphiphilic polymers. However, the high price to performance ratio of these methods can limit their industrial application. Herein, poly(glycidyl methacrylate) polymers of varying molecular weights were first synthesised by catalytic chain transfer polymerisation (CCTP). Amphiphilic polymers were then prepared using a simple one-pot, post-polymerisation modification process involving Michael-thiol addition in the presence of a range of hydrophobic mercaptans, followed by ring-opening of the epoxide groups with ethanolamine using microwave-assisted synthesis. This procedure allows for the synthesis of fully functional polymers within 3 hours. A range of well-defined materials are prepared and characterised by GPC, NMR, FTIR, DLS, TGA, and TEM

Dynamic crosslinked rubbers for a green future:A material perspective

Conventional rubber products, such as tires, seals, tubing, and damping systems are manufactured via a vulcanization process, which forms covalently crosslinked network structures and ensures mechanical robustness, thermal stability and chemical resistance. However, the covalent networks are permanent and these products cannot be reprocessed or reshaped, which makes vulcanised rubbers one of the major challenges facing waste management and the circular economy. To reduce waste pollution for products such as tires, conventional vulcanised rubbers must be replaced with reversibly crosslinked structures which are able to achieve mechanical robustness and chemical stability, whilst also being able to be reprocessed, reshaped, reused and recycled. State-of-the-art developments in supramolecular chemistry have shed light on a new generation of reprocessable elastomers and rubbers, which have the potential to tackle the long-standing issue of waste tire pollution. The introduction of dynamic covalent bonds or supramolecular interactions in traditional elastomers can produce reversibly crosslinked structures, where the synergy between the dynamic bonds in the network are carefully optimised to balance the ease of processing, mechanical properties, and structural stability. Furthermore, dynamic covalent bonds and supramolecular interactions can provide ‘living’ functions to elastomers, such as self-healing and stimuli-responsiveness. These properties can be further enhanced by the addition of nanofillers with tailored surface chemistry to provide a dual role as a dynamic crosslinker and reinforcing element. To create reprocessable and recyclable elastomers, the coupling of multiple dynamic interactions provides unlimited possibilities to optimise the structure and properties of recyclable rubbers. Here we critically overview the applications of dynamic chemistry in rubbers, with a focus on macromolecular design and strategies to balance the mechanical, functional (e.g. self-healing) and reprocessing properties.</p

Dynamic polymer networks : a new avenue towards sustainable and advanced soft machines

While the fascinating field of soft machines has grown rapidly over the last two decades, the materials they are constructed from have remained largely unchanged during this time. Parallel activities have led to significant advances in the field of dynamic polymer networks, leading to the design of three‐dimensionally cross‐linked polymeric materials that are able to adapt and transform through stimuli induced bond exchange. Recent work has begun to merge these two fields of research by incorporating the stimuli‐responsive properties of dynamic polymer networks into soft machine components. These include dielectric elastomers, stretchable electrodes, nanogenerators, and energy storage devices. In this minireview, we outline recent progress made in this emerging research boundary and discuss future directions for the field

Light scattering corrections to linear dichroism spectroscopy for liposomes in shear flow using calcein fluorescence and modified Rayleigh-Gans-Debye-Mie scattering

The interpretation of data from absorbance spectroscopy experiments of liposomes in flow systems is often complicated by the fact that there is currently no easy way to account for scattering artefacts. This has proved particularly problematic for linear dichroism (LD) spectroscopy, which may be used to determine binding modes of small molecules, peptides and proteins to liposomes if we can extract the absorbance signal from the combined absorbance/scattering experiment. Equations for a modified Rayleigh-Gans-Debye (RGD) approximation to the turbidity (scattering) LD spectrum are available in the literature though have not been implemented. This review summarises the literature and shows how it can be implemented. The implementation proceeds by first determining volume loss that occurs when a spherical liposome is subjected to flow. Calcein fluorescence can be used for this purpose since at high concentrations (> 60 mM) it has low intensity fluorescence with maxima at 525 and 563 nm whereas at low concentrations (<1 mM) the fluorescence intensity is enhanced and the band shifts to 536 nm. The scattering calculation process yields the average axis ratios of the distorted liposome ellipsoids and extent of orientation of the liposomes in flow. The scattering calculations require methods to estimate liposome integrity, volume loss, and orientation when subjected to shear stresses under flow

Structure and electrochemical properties of hierarchically porous carbon nanomaterials derived from hybrid ZIF-8/ZIF-67 bi-MOF coated cyclomatrix poly (organophosphazene) nanospheres

Hybrid bi-ZIF nanocrystals consisting of ZIF-8/ZIF-67 were synthesised in the presence of cyclomatrix poly(organophosphazene) (POP) nanospheres and formed POP/bi-ZIF core@shell nanospheres. The POP/bi-ZIF showed excellent thermal stability up to 478°C, with well-preserved core@shell structures during carbonization at 850°C. The resultant core@shell carbon nanospheres exhibited hierarchically mesoporous structures. The porous carbon core was derived from the carbonised covalent inorganic-organic polyphosphazene framework, containing in situ doped heteroatoms such as N, P, S and O; the shell structure was derived from the bi-ZIF containing up to 40% of Zn and Co elements. The bi-ZIF derived carbon shell showed a BET surface area of 1347.76 m² g-1 and a Langmuir surface area of 1882.71 m² g-1, and the total BET surface area of the core@shell structure reached 1025.00 m² g-1. When applied as an anode material in lithium ion batteries, the core@shell carbon structure reached a charge capacity of 595 mA h g-1 with a discharge capacity of 546 mA h g-1, and remained reversible charge/discharge capacity at 400 mA h g-1 after 140 cycles, which is higher than the theoretical capacity of graphite anode. A good cycling stability with 83% capacity retention in the C-rate tests was achieved. This work provides a facile and scalable method to produce mesoporous carbon nanostructures with in situ doped metal elements and heteroatoms, which benefits the high rate electrochemical properties of lithium ion batteries

Understanding the enhancement and temperature-dependency of the self-healing and electromechanical properties of dielectric elastomers containing mixed pendant polar groups

High permittivity self-healing dielectric elastomers have the potential to achieve long life, reusability, damage tolerance and enhanced energy density for energy harvesting devices and actuators. The self-healing performance of elastomers and usable temperature range can be affected by the chemical interactions present in the material. Self-healing thermoplastic elastomer styrene-butadiene-styrene (SBS) copolymers were prepared by introducing hydrogen bonding and electrostatic interactions through chemically grafting of polar groups to SBS: methyl thioglycolate (MG) and thioglycolic acid (TG). The mechanical properties were significantly affected by the strength of the hydrogen bonding network in the elastomers, whilst a high relative permittivity of εr ≈ 9.2 with a low loss of tan δ ≈ 0.01 was achieved. In addition, a disorder-to-order phase morphology transition was observed upon increasing the TG content due to the increased hydrogen-bonding network within SBS. At room temperature the self-healed 80/20 MG/TG-SBS exhibited a strain at break of 139% with a recovery ratio of 47.7%, and when healed at 80 °C for 3 hrs exhibited an increased strain at break of 230% with a recovery ratio of 79%. Analysis of FTIR and 1H NMR indicated that the presence of a stronger hydrogen bonding network increased the thermal resistance of the elastomers. The temperature-dependency of the self-healing behaviour was interpreted as the combined effect of hydrogen bonding, electrostatic interactions and chain interdiffusion. This work provides an in-depth understanding of how to tune the electromechanical and self-healing properties of elastomers by tailoring the type and concentration of pendent polar groups. It indicates that intrinsic modification is critical for the development of next generation high performance dielectric elastomers for actuator or energy harvesting devices operating at elevated temperatures