Multiscale structuring and characterisation of polyvinylidene difluoride based nanodielectrics

In the 21st century, the efficiency and sustainability of devices used for electrical energy storage presents a significant challenge for various technologies and industries. Despite many electrical devices and systems becoming more advanced, the components that power these systems are often based on technologies that have not substantially modernised over the past few decades. Dielectric polymers offer a new route for enhancing pulsed power delivery in electrical systems, offering a plethora of advantages over the industry standard ceramics that dominate the field, resolving both the sustainability and energy efficiency problems simultaneously. This project explores the potential of electrospun polyvinylidene difluoride (PVDF) nanofibre membranes for use in pulsed power devices. PVDF is notable due to the ferroelectric behaviour of its crystalline β-phase, which leads impressive energy storage properties in the polymer, allowing it to compete with commercial capacitors. This has led to the development of a variety of approaches to producing PVDF with a high β-phase content in recent years, with many endeavours producing near 100% β-phase content. Hence attention is now being paid to the subtleties of the crystalline nanostructure of PVDF, such as crystallite size and the orientation of crystallites to further bolster its energy storage potential. Here, the crystalline nanostructure of PVDF nanofibres is extensively explored under different processing conditions using materials characterisation techniques such as infrared spectroscopy, X-ray diffraction and scanning electron microscopy, while characterising the energy storage potential of these materials using . Correlations are drawn between processing conditions to crystalline nanostructure, and in turn nanostructure in relation to energy storage performance. Notably in this work, PVDF is electrospun using an ionic liquid in the electrospinning solution, which seeks to maximise the β-phase crystallinity and optimise the crystalline nanostructure of the nanofibre membranes at minimal additional time or cost investment. The unique morphology of the nanofibres is utilised to construct nanocomposites by coating the nanofibres with nanoparticles – in particular, metal organic frameworks (MOFs) – to further increase the energy storage potential of the nanofibre membranes. Finally, multilayer all-polymer laminate materials are constructed to prevent the high energy losses and low-field electrical breakdown experienced by electrospun PVDF nanofibre membranes when used for capacitive energy storage in isolation, as well as alleviating the mechanical fragility of the membranes. This thesis presents a route to creating highly ferroelectric polymer-based materials with impressive energy storage properties that could shape the future of materials in pulsed power devices

Effects of an ionic liquid and processing conditions on the ß-polymorph crystal formation in poly(vinylidene fluoride)

The piezoelectric properties of poly(vinylidene fluoride) (PVDF) are determined by the prevalence and orientation of its polar β-crystal phase, which can be tuned by processing conditions, additives, mechanical stretching or post-treatment. Here, the effects of three types of processing conditions on the crystalline structure evolution of PVDF were investigated; electrospinning, solution-casting and melt-compression. An ionic liquid (1-allyl-3-methylimidazolium chloride (AMIM)) used as an additive in aiding the electrospinning process, also affected the crystalline structure of the electrospun PVDF nanofibers. The total crystallinity, crystalline phase content and dielectric properties of the PVDF samples prepared by the different conditions were evaluated. The FTIR and DSC analyses show that the melt-compressed PVDF contains a high proportion of the paraelectric α-phase with a low total crystallinity, whereas the solution-cast PVDF contains a high proportion of polar γ-phase and a higher total crystallinity. In the case of the electrospun PVDF nanofibres, the addition of AMIM improved the morphology, uniformity and promoted the formation of the polar β and γ crystalline phases. X-Ray scattering analysis refined the crystal phase contents derived from FTIR, and also determined the ordered lamellar macromorphology formed by the three processing techniques. Furthermore, AMIM enhanced the a.c. conductivity and relative permittivity of the electrospun PVDF nanofibres by an order of magnitude, showing the effectiveness of using the ionic liquid AMIM, to improve the morphology and properties of electrospun PVDF nanofibers

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

Piezoelectric-driven self-sensing leaf-mimic actuator enabled by integration of a self-healing dielectric elastomer and a piezoelectric composite

Soft robots and devices exploit highly deformable materials that are capable of changes in shape to allow conformable physical contact for controlled manipulation. While soft robots are resilient to mechanical impact, they are susceptible to mechanical damage, such as tears and punctures. The development of self‐healing materials and actuators continues to attract increasing interest, in particular, with respect to integrating self‐healing polymers to create bioinspired soft self‐healing devices. Herein, a novel piezoelectric‐driven self‐healing leaf‐motion mimic actuator is designed by combining a thermoplastic methyl thioglycolate–modified styrene–butadiene–styrene (MGSBS) elastomer with a piezoelectric macrofiber composite (MFC) for self‐sensing applications. This article is the first demonstration of a self‐sensing and self‐healing actuator‐sensor system, which is driven by a piezoelectric actuator and can mimic leaf motion. The leaf‐motion actuator combines built‐in dynamic sensing and room‐temperature self‐healing capabilities to restore macroscale cutting damage with an intrinsically high bandwidth of up to 10 kHz. The feasibility and potential of the new actuator for use in complex soft autonomous systems are demonstrated. These new results help to address the emerging influence of self‐healing soft actuators and the challenges of sensing, actuation, and damage resistance in soft robotics

MouseBook: an integrated portal of mouse resources

The MouseBook (http://www.mousebook.org) databases and web portal provide access to information about mutant mouse lines held as live or cryopreserved stocks at MRC Harwell. The MouseBook portal integrates curated information from the MRC Harwell stock resource, and other Harwell databases, with information from external data resources to provide value-added information above and beyond what is available through other routes such as International Mouse Stain Resource (IMSR). MouseBook can be searched either using an intuitive Google style free text search or using the Mammalian Phenotype (MP) ontology tree structure. Text searches can be on gene, allele, strain identifier (e.g. MGI ID) or phenotype term and are assisted by automatic recognition of term types and autocompletion of gene and allele names covered by the database. Results are returned in a tabbed format providing categorized results identified from each of the catalogs in MouseBook. Individual result lines from each catalog include information on gene, allele, chromosomal location and phenotype, and provide a simple click-through link to further information as well as ordering the strain. The infrastructure underlying MouseBook has been designed to be extensible, allowing additional data sources to be added and enabling other sites to make their data directly available through MouseBook

Effectiveness of a national quality improvement programme to improve survival after emergency abdominal surgery (EPOCH): a stepped-wedge cluster-randomised trial

Background: Emergency abdominal surgery is associated with poor patient outcomes. We studied the effectiveness of a national quality improvement (QI) programme to implement a care pathway to improve survival for these patients. Methods: We did a stepped-wedge cluster-randomised trial of patients aged 40 years or older undergoing emergency open major abdominal surgery. Eligible UK National Health Service (NHS) hospitals (those that had an emergency general surgical service, a substantial volume of emergency abdominal surgery cases, and contributed data to the National Emergency Laparotomy Audit) were organised into 15 geographical clusters and commenced the QI programme in a random order, based on a computer-generated random sequence, over an 85-week period with one geographical cluster commencing the intervention every 5 weeks from the second to the 16th time period. Patients were masked to the study group, but it was not possible to mask hospital staff or investigators. The primary outcome measure was mortality within 90 days of surgery. Analyses were done on an intention-to-treat basis. This study is registered with the ISRCTN registry, number ISRCTN80682973. Findings: Treatment took place between March 3, 2014, and Oct 19, 2015. 22 754 patients were assessed for elegibility. Of 15 873 eligible patients from 93 NHS hospitals, primary outcome data were analysed for 8482 patients in the usual care group and 7374 in the QI group. Eight patients in the usual care group and nine patients in the QI group were not included in the analysis because of missing primary outcome data. The primary outcome of 90-day mortality occurred in 1210 (16%) patients in the QI group compared with 1393 (16%) patients in the usual care group (HR 1·11, 0·96–1·28). Interpretation: No survival benefit was observed from this QI programme to implement a care pathway for patients undergoing emergency abdominal surgery. Future QI programmes should ensure that teams have both the time and resources needed to improve patient care. Funding: National Institute for Health Research Health Services and Delivery Research Programme

Effectiveness of a national quality improvement programme to improve survival after emergency abdominal surgery (EPOCH): a stepped-wedge cluster-randomised trial

BACKGROUND: Emergency abdominal surgery is associated with poor patient outcomes. We studied the effectiveness of a national quality improvement (QI) programme to implement a care pathway to improve survival for these patients. METHODS: We did a stepped-wedge cluster-randomised trial of patients aged 40 years or older undergoing emergency open major abdominal surgery. Eligible UK National Health Service (NHS) hospitals (those that had an emergency general surgical service, a substantial volume of emergency abdominal surgery cases, and contributed data to the National Emergency Laparotomy Audit) were organised into 15 geographical clusters and commenced the QI programme in a random order, based on a computer-generated random sequence, over an 85-week period with one geographical cluster commencing the intervention every 5 weeks from the second to the 16th time period. Patients were masked to the study group, but it was not possible to mask hospital staff or investigators. The primary outcome measure was mortality within 90 days of surgery. Analyses were done on an intention-to-treat basis. This study is registered with the ISRCTN registry, number ISRCTN80682973. FINDINGS: Treatment took place between March 3, 2014, and Oct 19, 2015. 22 754 patients were assessed for elegibility. Of 15 873 eligible patients from 93 NHS hospitals, primary outcome data were analysed for 8482 patients in the usual care group and 7374 in the QI group. Eight patients in the usual care group and nine patients in the QI group were not included in the analysis because of missing primary outcome data. The primary outcome of 90-day mortality occurred in 1210 (16%) patients in the QI group compared with 1393 (16%) patients in the usual care group (HR 1·11, 0·96-1·28). INTERPRETATION: No survival benefit was observed from this QI programme to implement a care pathway for patients undergoing emergency abdominal surgery. Future QI programmes should ensure that teams have both the time and resources needed to improve patient care. FUNDING: National Institute for Health Research Health Services and Delivery Research Programme

Do suspended sediments modulate the effects of octylphenol on rainbow trout?

A system was devised which allows particles to remain in suspension in a conventional 60 L aquarium without undue disturbance to resident fish. Using this system, juvenile rainbow trout were exposed for one week to 4-tert-octylphenol (OP, 10-1000 µg/L) with or without the presence of suspended sediments (10-20 mg/L; collected from the River Calder, UK). About 8 % of the added OP partitioned to the solid phase. Vitellogenin levels were determined in the plasma of the exposed rainbow trout and showed a dose-dependent increase with regards to OP exposure concentration. Considerable variation in the vitellogenin response was observed between separate runs with the same OP concentration. There was no statistically significant (at P<0.05) difference in plasma VTG levels between the OP treatments with or without suspended sediments. This suggests that the dissolved concentration is the key factor and natural suspended sediment neither protects against, nor exacerbates, the endocrine disrupting effect of OP on fish