Polymers with the ability to repair themselves after sustaining damage could extend the lifetimes of materials used in many applications 1 . Most approaches to healable materials require heating the damaged area [2][3][4] . Here we present metallosupramolecular polymers that can be mended through exposure to light. They consist of telechelic, rubbery, low-molecular-mass polymers with ligand end groups that are non-covalently linked through metal-ion binding. On exposure to ultraviolet light, the metal-ligand motifs are electronically excited and the absorbed energy is converted into heat. This causes temporary disengagement of the metal-ligand motifs and a concomitant reversible decrease in the polymers' molecular mass and viscosity 5 , thereby allowing quick and efficient defect healing. Light can be applied locally to a damage site, so objects can in principle be healed under load. We anticipate that this approach to healable materials, based on supramolecular polymers and a light-heat conversion step, can be applied to a wide range of supramolecular materials that use different chemistries.The healing of cracks in amorphous polymers by heating above the glass transition temperature (T g ) involves surface rearrangement and approach of polymer chains, followed by wetting, diffusion and reentanglement of the chains 6 . Because the rates of the final two steps are inversely proportional to the molecular mass, healing is generally slow and inefficient. This problem can be overcome by exploiting thermally reversible, covalent bonds 7,8 or non-covalent supramolecular motifs 5,9,10 that allow the reaction equilibrium to be temporarily shifted to lower-molecular-mass species 11 on exposure to heat. This reduces the viscosity of the material, such that defects can be mended, before the equilibrium is shifted back and the polymer is reformed. Supramolecular polymers that phase separate into physically crosslinked networks (Fig. 1a) should be especially well suited for this purpose, because such morphologies generally bestow the material with high toughness. The supramolecular motifs can disengage in the solid state on exposure to heat or a competitive binding agent 12,13 , causing disassembly into small molecules 14 and viscosity reductions. Reporting a series of supramolecular materials formed by metal-ligand interactions, we demonstrate here that this architecture is an excellent basis for elastomeric materials in which defects can be efficiently repaired. We show that the use of light 15 as a stimulus for the dissociation of supramolecular motifs has distinct advantages over thermally healable systems, including the possibility of exclusively exposing and healing the damaged region.The new polymers are based on a macromonomer comprising a rubbery, amorphous poly(ethylene-co-butylene) core with 2,6-bis(19-methylbenzimidazolyl)pyridine (Mebip) ligands at the termini (Fig. 1b, 3). This design was based on the assumption that the hydrophobic core and the polar metal-ligand motif would phase separate 16 . Metal-Mebip com...

The rapid development of additive manufacturing techniques, also known as three‐dimensional (3D) printing, is driving innovations in polymer chemistry, materials science, and engineering. Among current 3D printing techniques, direct ink writing (DIW) employs viscoelastic materials as inks, which are capable of constructing sophisticated 3D architectures at ambient conditions. In this perspective, polymer designs that meet the rheological requirements for direct ink writing are outlined and successful examples are summarized, which include the development of polymer micelles, co‐assembled hydrogels, supramolecularly cross‐linked systems, polymer liquids with microcrystalline domains, and hydrogels with dynamic covalent cross‐links. Furthermore, advanced polymer designs that reinforce the mechanical properties of these 3D printing materials, as well as the integration of functional moieties to these materials are discussed to inspire new polymer designs for direct ink writing and broadly 3D printing.

Ionic polymer transducers (IPT) based on electroactive polymers (EAP) display electromechanical coupling that enables breakthroughs in the design of high-performance actuators and sensors. The ion-exchange membrane Nafion remains as the benchmark for a majority of research and development in IPT technology. Advances in IPT performance, elemental understanding of transduction mechanisms, and the development of future technologies (e.g., artificial muscles) are largely due to significant efforts to tailor complementary transducer compositions relative to commercially available Nafion. Current fundamental advances in the synthesis, characterization, and application of tailored ion-containing polymers are reviewed for increased performance, decreased cost, and improved processing of IPTs. Recent attention to the correlation of morphological structure to ion conduction mechanisms has led to new paradigms for performance. Tailoring of ionomeric membranes to isolate material interactions within the composite IPT that contribute to performance is also highlighted. Novel compositions such as ion-containing polysulfones, poly(ethylene-co-vinyl alcohol), polystyrene, and fluorinated acrylic copolymers have broadened the range of electromechanical performance. This perspective discusses recent research efforts and rapidly emerging fundamental understanding of the tailored synthesis of ionomers for IPTs. However, further studies are necessary to confirm the mechanisms that drive these devices under an array of compositions and geometries in emerging applications.

Biodiesel fuels may serve as a partial solution in the search for sustainable energy sources for the transportation sector. However, increased nitrogen oxide (NO x ) emissions are a potentially significant drawback to the use of biodiesel fuels that must be addressed if biodiesel is to gain widespread acceptance. One approach is to identify specific biodiesel fuel properties that minimize NO x formation and use these to produce lower NO x fuel blends. In this work, seven biodiesel fuels were produced from high-erucic rapeseed, olive, palm, coconut, soybean, and fresh and used canola oils, with their chemical composition determined using gas chromatography−mass spectrometry (GC−MS). The fuels were then burned in a single-cylinder directinjection diesel engine and evaluated for both fuel consumption and exhaust emissions of nitrogen oxides, carbon monoxide (CO), unburned hydrocarbons, and particulate matter. While all biodiesels had higher brake-specific nitric oxide (NO) emissions than ultralow sulfur diesel (ULSD) at low engine loads, olive, palm, coconut, and canola biodiesels performed better than ULSD at 50% loading and above. Nitrogen dioxide (NO 2 ), CO, and unburned hydrocarbon emissions were generally lower from the biodiesel fuels than ULSD. Palm biodiesel consistently generated the lowest brake-specific NO x levels of all tested fuels. Statistical analysis of the results showed that higher fuel hydrogen/carbon molar ratios, low polyunsaturation levels, and lower fuel density were all significantly associated with reduced NO emissions in the tested biodiesel fuels but no clear trends were observed for NO 2 . The results suggest that pathways exist for tailoring the fuel properties of biodiesel blends to reduce nitrogen oxide emission compared to current fuels.

Zwitterionomers containing less than 13 mol % zwitterion functionality were synthesized using free radical copolymerization of n-butyl acrylate (nBA) and sulfobetaine monomers. X-ray scattering results revealed a two-phase morphology, which is typical of random ionomers with an ionomer peak at q ∼1.5 nm -1 . Swelling studies in the ionic liquid (IL), 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES), showed an influence of zwitterionic structure on IL uptake. Zwitterionomer membranes were swollen to various IL contents, and the influence of IL on mechanical properties, morphology, and ionic conductivity was explored through dynamic mechanical analysis (DMA), X-ray scattering, and impedance spectroscopy, respectively. Results revealed that IL preferentially swelled the zwitterionic domains but was excluded from the matrix phase. Significant changes in mechanical properties and ionic conductivity were observed above a critical uptake of IL. Fundamental explorations of the interaction of ILs with sulfobetaine-containing copolymers may lead to the use of zwitterionomers in emerging membrane applications.

Covalently linked single-crystalline porous organic materials are highly desired for structure-property analysis, however, periodically polymerizing organic entities into high dimensional networks is challenging. Here, we report a series of topologically divergent single-crystalline hydrogen-bonded crosslinked organic frameworks (HCOFs) with visible guestinduced elastic expansions, which mutually integrate high structural order and high flexibility into one framework. These HCOFs are synthesized by photo-crosslinking molecular crystals with alkyldithiols of different chain lengths. Their detailed structural information was revealed by single-crystal X-ray analysis and experimental investigations of HCOFs and their corresponding single-crystalline analogues. Upon guest adsorption, HCOF-2 crystals comprised of a 3D self-entangled polymer network undergo anisotropic expansion to more than twice their original size, while the 2D-bilayer HCOF-3 crystals exhibit visible, layered sorption bands and form delaminated sheets along the plane of its 2D layers. The dynamic expansion of HCOF networks creates guest-induced porosity with over 473 % greater volume than their permanent voids, as calculated from their record-breaking aqueous iodine adsorption capacities. Temperature-gated DMSO sorption investigations illustrated that the flexible nature of crosslinkers in HCOFs provides positive entropy from the coexistence of multiple conformations to allow for elastic expansion and contraction of the frameworks.

Current and future injector designs for diesel engines approach pressures of greater than 100 MPa. However, the high-pressure physical properties, such as viscosity, of biologically derived diesel fuel (biodiesel) are nearly absent in the literature. This study focuses on the viscosity of biodiesel samples, fatty acid methyl esters (FAMEs), derived from soybean oil, soybean oil from Vistive soybeans, canola oil, recycled canola oil that has been used in cooking and frying, and coconut oil from 283.15 to 373.15 K and pressures up to 131 MPa. Petroleum-derived diesel (ultra-low sulfur, number 2 diesel) has also been investigated to compare to the biodiesel samples. The viscosity of the samples increases linearly with pressure until approximately 35 MPa, followed by a higher order response to pressure. Except for coconut-oil-derived biodiesel, the biodiesel samples have viscosities that are greater than petroleum-derived diesel at both ambient and elevated pressures. However, at lower temperatures and high pressures, the diesel and biodiesel samples become more similar. The viscosity of the biodiesel samples with pressure can increase nearly 300% over the pressure range investigated over their respective ambient-pressure viscosity; number 2 diesel increases up to ∼400% over similar pressures. The biodiesel samples at 283.15 K were found to experience pressure-induced cloud points (solid−liquid equilibrium) from 70 to 100 MPa, which significantly increases their viscosity. The Tait−Litovitz equation was found to correlate the data very well over the large range of both temperature and pressure.

ObjectiveIn this study, we describe the pattern of bed occupancy across England during the peak of the first wave of the COVID-19 pandemic.DesignDescriptive survey.SettingAll non-specialist secondary care providers in England from 27 March27to 5 June 2020.ParticipantsAcute (non-specialist) trusts with a type 1 (ie, 24 hours/day, consultant-led) accident and emergency department (n=125), Nightingale (field) hospitals (n=7) and independent sector secondary care providers (n=195).Main outcome measuresTwo thresholds for ‘safe occupancy’ were used: 85% as per the Royal College of Emergency Medicine and 92% as per NHS Improvement.ResultsAt peak availability, there were 2711 additional beds compatible with mechanical ventilation across England, reflecting a 53% increase in capacity, and occupancy never exceeded 62%. A consequence of the repurposing of beds meant that at the trough there were 8.7% (8508) fewer general and acute beds across England, but occupancy never exceeded 72%. The closest to full occupancy of general and acute bed (surge) capacity that any trust in England reached was 99.8% . For beds compatible with mechanical ventilation there were 326 trust-days (3.7%) spent above 85% of surge capacity and 154 trust-days (1.8%) spent above 92%. 23 trusts spent a cumulative 81 days at 100% saturation of their surge ventilator bed capacity (median number of days per trust=1, range: 1–17). However, only three sustainability and transformation partnerships (aggregates of geographically co-located trusts) reached 100% saturation of their mechanical ventilation beds.ConclusionsThroughout the first wave of the pandemic, an adequate supply of all bed types existed at a national level. However, due to an unequal distribution of bed utilisation, many trusts spent a significant period operating above ‘safe-occupancy’ thresholds despite substantial capacity in geographically co-located trusts, a key operational issue to address in preparing for future waves.