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"Stephen, Craig"
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Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning
Cephalopods can display dazzling patterns of colours by selectively contracting muscles to reversibly activate chromatophores – pigment-containing cells under their skins. Inspired by this novel colouring strategy found in nature, we design an electro-mechano-chemically responsive elastomer system that can exhibit a wide variety of fluorescent patterns under the control of electric fields. We covalently couple a stretchable elastomer with mechanochromic molecules, which emit strong fluorescent signals if sufficiently deformed. We then use electric fields to induce various patterns of large deformation on the elastomer surface, which displays versatile fluorescent patterns including lines, circles and letters on demand. Theoretical models are further constructed to predict the electrically induced fluorescent patterns and to guide the design of this class of elastomers and devices. The material and method open promising avenues for creating flexible devices in soft/wet environments that combine deformation, colorimetric and fluorescent response with topological and chemical changes in response to a single remote signal.
Cephalopods change colour by mechanically activating chromatophores via muscle contraction. Here, the authors use a similar concept for flexible displays, where electric field control over elastomer strain allows activation of mechanophores and provides on-demand and variable fluorescent patterns.
Journal Article
Mechanical gating of a mechanochemical reaction cascade
Covalent polymer mechanochemistry offers promising opportunities for the control and engineering of reactivity. To date, covalent mechanochemistry has largely been limited to individual reactions, but it also presents potential for intricate reaction systems and feedback loops. Here we report a molecular architecture, in which a cyclobutane mechanophore functions as a gate to regulate the activation of a second mechanophore, dichlorocyclopropane, resulting in a mechanochemical cascade reaction. Single-molecule force spectroscopy, pulsed ultrasonication experiments and DFT-level calculations support gating and indicate that extra force of >0.5 nN needs to be applied to a polymer of gated
g
DCC than of free
g
DCC for the mechanochemical isomerization
g
DCC to proceed at equal rate. The gating concept provides a mechanism by which to regulate stress-responsive behaviours, such as load-strengthening and mechanochromism, in future materials designs.
Polymer mechanochemistry offers opportunities to control and engineer desired chemical transformations. Here, Craig and co-workers present a mechanical gating system whereby one mechanophore modulates the reactivity of another, resulting in a mechanochemical cascade reaction.
Journal Article
Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization
The mechanical degradation of polymers is typically limited to a single chain scission per triggering chain stretching event, and the loss of stress transfer that results from the scission limits the extent of degradation that can be achieved. Here, we report that the mechanically triggered ring-opening of a [4.2.0]bicyclooctene (BCOE) mechanophore sets up a delayed, force-free cascade lactonization that results in chain scission. Delayed chain scission allows many eventual scission events to be initiated within a single polymer chain. Ultrasonication of a 120 kDa BCOE copolymer mechanically remodels the polymer backbone, and subsequent lactonization slowly (~days) degrades the molecular weight to 4.4 kDa, > 10× smaller than control polymers in which lactonization is blocked. The force-coupled kinetics of ring-opening are probed by single molecule force spectroscopy, and mechanical degradation in the bulk is demonstrated. Delayed scission offers a strategy to enhanced mechanical degradation and programmed obsolescence in structural polymeric materials.
The mechanical degradation of polymers is typically limited to a single chain scission event and the loss of stress transfer during the scission process limits the extent of degradation achieved. Here, the authors report a mechanically triggered, delayed scission strategy that allows many eventual scission events to be initiated within a single polymer chain.
Journal Article
Urban allies : ten brand-new collaborative stories
These collaborative stories unite two beloved characters from two different urban fantasy series in each of ten electrifying new stories.
Book
The role of polymer mechanochemistry in responsive materials and additive manufacturing
The use of mechanical forces to chemically transform polymers dates back decades. In recent years, the use of mechanochemistry to direct constructive transformations in polymers has resulted in a range of engineered molecular responses that span optical, mechanical, electronic and thermal properties. The chemistry that has been developed is now well positioned for use in materials science, polymer physics, mechanics and additive manufacturing. Here, we review the historical backdrop of polymer mechanochemistry, give an overview of the existing toolbox of mechanophores and associated theoretical methods, and speculate as to emerging opportunities in materials science for which current capabilities are seemingly well suited. Non-linear mechanical responses and internal, amplifying stimulus–response feedback loops, including those enabled by, or coupled to, microstructured metamaterial architectures, are seen as particularly promising.
Polymer mechanochemistry converts mechanical forces in materials to chemical reactions through the response of functional groups known as mechanophores. This Review discusses the colorimetric, mechanical, chemical and electronic responses of mechanophores that may be useful in materials for strain sensing and strengthening, soft devices and additive manufacturing.
Journal Article
Distal conformational locks on ferrocene mechanophores guide reaction pathways for increased mechanochemical reactivity
Mechanophores can be used to produce strain-dependent covalent chemical responses in polymeric materials, including stress strengthening, stress sensing and network remodelling. In general, it is desirable for mechanophores to be inert in the absence of force but highly reactive under applied tension. Metallocenes possess potentially useful combinations of force-free stability and force-coupled reactivity, but the mechanistic basis of this reactivity remains largely unexplored. Here, we have used single-molecule force spectroscopy to show that the mechanical reactivities of a series of ferrocenophanes are not correlated with ring strain in the reactants, but with the extent of rotational alignment of their two cyclopentadienyl ligands. Distal attachments can be used to restrict the mechanism of ferrocene dissociation to proceed through ligand ‘peeling’, as opposed to the more conventional ’shearing’ mechanism of the parent ferrocene, leading the dissociation rate constant to increase by several orders of magnitude at forces of ~1 nN. It also leads to improved macroscopic, multi-responsive behaviour, including mechanochromism and force-induced cross-linking in ferrocenophane-containing polymers.Metallocenes are attractive mechanophores because they are stable in the absence of force, yet reactive under tension. Now, covalently bridging the two cyclopentadienyl (Cp) ligands of ferrocenes embedded in a polymer has been shown to alter their mechanochemical reactivity, leading to a faster dissociation of the Fe–Cp bond, which occurs through a peeling mechanism rather than a shearing one.
Journal Article
