5 research outputs found
Synthesis and evaluation of a silver nanoparticle/polyurethane composite that exhibits antiviral activity against SARS-CoV-2
In this proof-of-concept study, we aim to produce a polyurethane (PU)-based composite that can reduce the amount of viable SARS-CoV-2 virus in contact with the surface of the polymeric film without further interventions such as manual cleaning. Current protocols for maintaining the hygiene of commonly used touchpoints (door handles, light switches, shop counters) typically rely on repeated washing with antimicrobial products. Since the start of the SARS-CoV-2 pandemic, frequent and costly surface sanitization by workers has become standard procedure in many public areas. Therefore, materials that can be retrofitted to touchpoints, yet inhibit pathogen growth for extended time periods are an important target. Herein, we design and synthesise the PU using a one-pot synthetic procedure on a multigram scale from commercial starting materials. The PU forms a robust composite thin film when loaded with 10 wt% silver nanoparticles (AgNPs). The addition of AgNPs increases the ultimate tensile strength, modules of toughness and modulus of elasticity at the cost of a reduced elongation at break when compared to the pristine PU. Comparative biological testing was carried out by the addition of pseudotyped virus (PV) bearing the SARS-CoV-2 beta (B.1.351) VOC spike protein onto the film surfaces of either the pristine PU or the PU nanocomposite. After 24 h without further human intervention the nanocomposite reduced the amount of viable virus by 67% (p = 0.0012) compared to the pristine PU treated under the same conditions. The significance of this reduction in viable virus load caused by our nanocomposite is that PUs form the basis of many commercial paints and coatings. Therefore, we envisage that this work will provide the basis for further progress towards producing a retrofittable surface that can be applied to a wide variety of common touchpoints
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Conjugated, rod-like viologen oligomers: correlation of oligomer length with conductivity and photoconductivity
An iterative synthesis has been used to produce conjugated, monodisperse, viologen-based aromatic oligomers containing up to 12 aromatic/heterocyclic rings. The methoxy-substituted oligomers were soluble in common organic solvents and could be processed by spin coating. The conductivities of the resulting films (30 to 221 nm thick) increased by more than an order of magnitude as the oligomer length increased from unimer (1, 2.20×10-11 S cm-1) through dimer (2) to trimer (3, 6.87×10-10 S cm-1). The bandgaps of the materials were estimated from the absorption spectra of these thin films. The longest oligomer, 3, exhibited a noticeably narrower bandgap (2.3 eV) than the shorter oligomers (1 and 2 both 2.7 eV). Oligomer 3 also showed photoconductivity under irradiation across a wide range of wavelengths in the visible spectral region. In conjunction with DFT calculations of these systems our results suggest that structurally related viologen-type oligomers may find use in optoelectronic devices
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Fluoride-responsive debond on demand adhesives: manipulating polymercrystallinity and hydrogen bonding to optimise adhesion strength at lowbonding temperatures
This paper reports the solvent-free synthesis of a series of sixfluoride responsive debond-on-demand poly-urethane (PU) adhesives that contain a silyl functionalised degradable unit (DU). To optimise the adhesionstrength and debonding nature of the adhesives, the chemical composition of the PUs was varied according tothe structure of the polyol or the diisocyanate component in the polymer mainchain.1H NMR spectroscopy wasused to study the depolymerisation behaviour in solution state. It showed thattetra-butylammoniumfluoride(TBAF) triggered the breakdown of the DU unit without fragmenting the polyol mainchain indiscriminately. Onexposure tofluoride ions, the PUs underwent depolymerisation with reductions in Mnranging from 64 to 90% asmeasured by GPC analysis. The morphology and thermal properties of the PUs were characterised by differentialscanning calorimetry (DSC), rheology and variable temperature (VT) SAXS/WAXS analysis. Each techniquedemonstrated the reversibility of the supramolecular polymer network under thermal stimuli. PUs containingpoly(butadiene) soft segments were amorphous with glass transition and viscoelastic transition temperaturesdependent on the nature of the soft segment and diisocyanate starting materials. The PU containing a polyestersoft segment exhibited a defined melting point at 49 °C. Mechanical stress-strain analysis of the series of PUsshowed each exhibited greater than 70% reduction in toughness after treatment with TBAF for 30 min as aconsequence of the chemo-responsive degradation of the polymer mainchain. The material featuring an ester-based polyol demonstrated excellent adhesion at bonding temperatures as low as 60 °C. Moreover, this materialcould be thermally rebonded if broken by force without loss in adhesion strength over three debond-rebondcycles. Lap shear adhesion tests showed a reduction in adhesive strength of approximately 40% (from 11.4 MPato 7.3 MPa) on exposure tofluoride ion
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Composite polyurethane adhesives that debond-on-demand by hysteresis heating in an oscillating magnetic field
Debond-on-demand adhesives are an emerging industrially important technology, allowing components and materials to be readily separated when required, facilitating recycling. Herein, a composite adhesive has been synthesized that can undergo hysteresis heating to debond-on-demand through direct exposure to an oscillating magnetic field. The adhesive is composed of a polyurethane continuous phase with commercial, unfunctionalized iron oxide particles as the filler (between 1 and 20 wt%). 2 mg of the composite containing 8 wt% iron oxide particles was able to bond various surfaces including glass, wood, aluminium and polyvinyl chloride and support a static load of 100 g. The composites were fabricated by melt processing which resulted in a relatively inhomogeneous dispersion of particles. The values of the Young’s modulus, the ultimate tensile strength, modulus of toughness of the adhesives were comparable to those exhibited by a commercial hot melt adhesive but relatively invariant over the series of composites examined. When subjected to hysteresis heating from an oscillating magnetic field, the rate of temperature increase was dependent on the loading level of Fe3O4. Debonding times decreased from approximately 5 min to less than 30 s exposure to the oscillating magnetic field as the Fe3O4 loading level increased from 1 to 20%. These results will help guide the design of new debond-on-demand polymers that can be addressed through exposure to an oscillating magnetic field
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A macrocyclic receptor containing two viologen species connected by conjugated terphenyl groups
A macrocyclic receptor molecule containing two viologen species connected by conjugated terphenyl groups has been designed and synthesised. The single-crystal X-ray structure shows that the two viologen residues have a transannular N…N separation of ca. 7.4 Å. Thus, the internal cavity dimensions are suitable for the inclusion of -electron-rich species. The macrocycle is redox active, and can accept electrons from suitable donor species including triethylamine, resulting in a dramatic colour change from pale yellow to dark green as a consequence of the formation of a paramagnetic bis(radical cationic) species. Cyclic voltammetry shows that the macrocycle can undergo two sequential and reversible reduction processes (E1/2 = -0.65 and -0.97 V vs Fc/Fc+). DFT and TD-DFT studies accurately replicate the structure of the tetracationic macrocycle and the electronic absorption spectra the three major redox states of the system. These calculations also showed that during electrochemical reduction, the unpaired electron density of the radical cations remains relatively localised within the heterocyclic rings. The ability of the macrocycle to form supramolecular complexes was confirmed by the formation of a pseudorotaxane with a guest molecule containing a -electron-rich 1,5-dihydroxynaphthalene derivative. Threading and dethreading of the pseudorotaxane was fast on the NMR timescale, and the complex exhibited an association constant of 150 M-1 (± 30 M-1) as calculated from 1H NMR titration studies