Electron-electron interactions can render an otherwise conducting material insulating, with the insulator-metal phase transition in correlated-electron materials being the canonical macroscopic ...manifestation of the competition between charge-carrier itinerancy and localization. The transition can arise from underlying microscopic interactions among the charge, lattice, orbital and spin degrees of freedom, the complexity of which leads to multiple phase-transition pathways. For example, in many transition metal oxides, the insulator-metal transition has been achieved with external stimuli, including temperature, light, electric field, mechanical strain or magnetic field. Vanadium dioxide is particularly intriguing because both the lattice and on-site Coulomb repulsion contribute to the insulator-to-metal transition at 340 K (ref. 8). Thus, although the precise microscopic origin of the phase transition remains elusive, vanadium dioxide serves as a testbed for correlated-electron phase-transition dynamics. Here we report the observation of an insulator-metal transition in vanadium dioxide induced by a terahertz electric field. This is achieved using metamaterial-enhanced picosecond, high-field terahertz pulses to reduce the Coulomb-induced potential barrier for carrier transport. A nonlinear metamaterial response is observed through the phase transition, demonstrating that high-field terahertz pulses provide alternative pathways to induce collective electronic and structural rearrangements. The metamaterial resonators play a dual role, providing sub-wavelength field enhancement that locally drives the nonlinear response, and global sensitivity to the local changes, thereby enabling macroscopic observation of the dynamics. This methodology provides a powerful platform to investigate low-energy dynamics in condensed matter and, further, demonstrates that integration of metamaterials with complex matter is a viable pathway to realize functional nonlinear electromagnetic composites.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This work details the development of a cotton fabric functionalized with UiO-66-NH2 metal–organic framework (MOF). The materials were made by seeding the growth of the MOF on the cotton by first ...bonding zirconium (Zr) to the surface of the fabric utilizing cyanuric chloride modified with a thiol. After seeding the fabrics with Zr, UiO-66-NH2 was grown on the fabric using a hydrothermal method. Several different routes of attaching Zr to cyanuric chloride were examined. Scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) data are consistent with UiO-66-NH2, and the fabrics have surface areas between 45 and 125 m2/g depending on the synthetic conditions used to produce the materials. The functionalized cotton reacts with dimethyl 4-nitrophenyl phosphate (DMNP), a chemical nerve agent simulant, as monitored by UV–vis spectroscopy. The results illustrate that MOF–fiber composites can be created using natural fibers, and the resulting composites provide similar chemical warfare agent (CWA) simulant reactivity as observed on composites of MOFs and synthetic polymers..
In previous work with thermally robust salts Cassity
et al., Phys. Chem. Chem. Phys.
, 2017,
19
, 31560 it was noted that an increase in the dipole moment of the cation generally led to a decrease in ...the melting point. Molecular dynamics simulations of the liquid state revealed that an increased dipole moment reduces cation-cation repulsions through dipole-dipole alignment. This was believed to reduce the liquid phase enthalpy, which would tend to lower the melting point of the IL. In this work we further test this principle by replacing hydrogen atoms with fluorine atoms at selected positions within the cation. This allows us to alter the electrostatics of the cation without substantially affecting the sterics. Furthermore, the strength of the dipole moment can be controlled by choosing different positions within the cation for replacement. We studied variants of four different parent cations paired with bistriflimide and determined their melting points, and enthalpies and entropies of fusion through DSC experiments. The decreases in the melting point were determined to be enthalpically driven. We found that the dipole moment of the cation, as determined by quantum chemical calculations, is inversely correlated with the melting point of the given compound. Molecular dynamics simulations of the crystalline and solid states of two isomers showed differences in their enthalpies of fusion that closely matched those seen experimentally. Moreover, this reduction in the enthalpy of fusion was determined to be caused by an increase in the enthalpy of the crystalline state. We provide evidence that dipole-dipole interactions between cations leads to the formation of cationic domains in the crystalline state. These cationic associations partially block favourable cation-anion interactions, which are recovered upon melting. If, however, the dipole-dipole interactions between cations is too strong they have a tendency to form glasses. This study provides a design rule for lowering the melting point of structurally similar ILs by altering their dipole moment.
Adjusting the dipole moment of an ionic liquid cation through fluorine substitution for hydrogen tunes the melting point.
Poly(ester amide)s (PEAs) bearing various side chains were synthesized by post-polymerization modification of
PA-1
, a vinylidene containing PEA. The thiols 1-dodecanethiol (1A-SH), ...2-phenylethanethiol (1B-SH), 2-mercaptoethanol (1C-SH), thioglycolic acid (1D-SH), furfuryl mercaptan (1E-SH) and sodium-2-mercaptoethanesulfonate (1F-SH) were reacted with
PA-1
to form PEAs
PA-1A
through
PA-1F
respectively. PEAs containing non-polar thiol side chains (
PA-1A
,
PA-1B
,
PA-1E
), showed little change in solubility compared to
PA-1
, while PEAs with more polar side chains improved solubility in more polar solvents.
PA-1F
, functionalized with sodium-2-mercaptoethanesulfonate, became water-soluble. The introduction of pendant functional groups impacted the thermal behaviors of PEAs in a wide range. The PEAs were thermally stable up to 368 °C, with glass transition temperatures (
T
g
) measured between 117 to 152 °C. Moreover, to demonstrate the versatility of the PEAs, thermal reprocessable networks and polyurethanes were successfully fabricated by reacting with a bismaleimide (1,6-bis(maleimido)hexane,
1,6-BMH
) and a diisocyanate (4,4′-diphenylmethane diisocyanate,
4,4′-MDI
), respectively. This study paves the way for the facile synthesis of functional poly(ester amide)s with great potential in many fields.
Poly(ester amide)s with tunable properties were synthesized
via
post-polymerization thiol-ene modification of a bio-sourced vinylidene containing poly(ester amide).
Thermally robust materials have been of interest since the middle of the past century for use as high temperature structural materials, lubricants, heat transfer fluids and other uses where thermal ...stability is necessary or desirable. More recently, ionic liquids have been described as 'thermally robust,' with this moniker often originating from their low volatility rather than their innate stability. As many ionic liquids have vanishingly low vapor pressures, the upper limit of their liquid state is commonly considered to be their degradation temperature, frequently reported from TGA measurements. The short duration ramps often used in TGA experiments can significantly overestimate the temperature at which significant degradation begins to occur when the compounds are held isothermal for even a few hours. Here, we review our recent work, and that of colleagues, in developing thermally robust ionic compounds, primarily perarylphosphonium and perarylsulfonium bistriflimide salts, in some of which cation stability exceeds that of the anion. We have used a combination of molecular design, synthesis, and computational modeling to understand the complex tradeoffs involving thermal stability, low melting point and other desirable physicochemical properties.
Resveratrol is a phytochemical with chemopreventive activity in preclinical rodent models of colorectal carcinogenesis. Antiproliferation is one of the many chemopreventive modes of action it has ...been shown to engage in. Concentrations of resveratrol, which can be achieved in human tissues after p.o. administration, have not yet been defined. The purpose of this study was to measure concentrations of resveratrol and its metabolites in the colorectal tissue of humans who ingested resveratrol. Twenty patients with histologically confirmed colorectal cancer consumed eight daily doses of resveratrol at 0.5 or 1.0 g before surgical resection. Resveratrol was found to be well tolerated. Normal and malignant biopsy tissue samples were obtained before dosing. Parent compound plus its metabolites resveratrol-3-O-glucuronide, resveratrol-4'-O-glucuronide, resveratrol-3-O-sulfate, resveratrol-4'-O-sulfate, resveratrol sulfate glucuronide, and resveratrol disulfate were identified by high-performance liquid chromatography (HPLC) with UV or mass spectrometric detection in colorectal resection tissue. Quantitation was achieved by HPLC/UV. Cell proliferation, as reflected by Ki-67 staining, was compared in preintervention and postintervention tissue samples. Resveratrol and resveratrol-3-O-glucuronide were recovered from tissues at maximal mean concentrations of 674 and 86.0 nmol/g, respectively. Levels of resveratrol and its metabolites were consistently higher in tissues originating in the right side of the colon compared with the left. Consumption of resveratrol reduced tumor cell proliferation by 5% (P = 0.05). The results suggest that daily p.o. doses of resveratrol at 0.5 or 1.0 g produce levels in the human gastrointestinal tract of an order of magnitude sufficient to elicit anticarcinogenic effects. Resveratrol merits further clinical evaluation as a potential colorectal cancer chemopreventive agent.
Sub‐micrometer/nanoscale patterned polymer brushes are prepared by employing cucurbit8uril (CB8) as a supramolecular recognition motif to assemble functional silica colloids onto Au surfaces as a ...sacrificial nanopatterning template. By employing CB8‐mediated host–guest interactions at the interface, it is possible to readily generate nanopatterned materials in aqueous media under ambient conditions.
Dynamic Combinatorial Chemistry Corbett, Peter T; Leclaire, Julien; Vial, Laurent ...
Chemical reviews,
09/2006, Letnik:
106, Številka:
9
Journal Article
Recenzirano
Dynamic combinatorial chemistry is defined as combinatorial chemistry under thermodynamic control. One application, which this review discusses, is the identification of the most stable structure in ...mixtures of structures with difference conformational properties.
Radiation‐resistant but cost‐efficient, flexible, and ultralight solar sheets with high specific power (W g−1) are the “holy grail” of the new space revolution, powering private space exploration, ...low‐cost missions, and future habitats on Moon and Mars. Herein, this study investigates an all‐perovskite tandem photovoltaic (PV) technology that uses an ultrathin active layer (1.56 µm) but offers high power conversion efficiency, and discusses its potential for high‐specific‐power applications. This study demonstrates that all‐perovskite tandems possess a high tolerance to the harsh radiation environment in space. The tests under 68 MeV proton irradiation show negligible degradation (<6%) at a dose of 1013 p+ cm−2 where even commercially available radiation‐hardened space PV degrade >22%. Using high spatial resolution photoluminescence (PL) microscopy, it is revealed that defect clusters in GaAs are responsible for the degradation of current space‐PV. By contrast, negligible reduction in PL of the individual perovskite subcells even after the highest dose studied is observed. Studying the intensity‐dependent PL of bare low‐gap and high‐gap perovskite absorbers, it is shown that the VOC, fill factor, and efficiency potentials remain identically high after irradiation. Radiation damage of all‐perovskite tandems thus has a fundamentally different origin to traditional space PV.
Efficient all‐perovskite‐based tandem photovoltaics (PV) are shown to be radiation hard, surpassing state‐of‐the‐art industry‐standard space PV. Combining high specific power with good resilience to the harsh radiation environment in space, they promise a next‐generation of lightweight and cost‐efficient solutions to power private space exploration, low‐cost missions as well as future habitats on the Moon and Mars.
"The Snows of Kilimanjaro" and "One Reader Writes," although very different in their reception histories, nevertheless share a crucial verbal and thematic parallel: each story contains similarly ...worded speculation on how a particular illness (gangrene and syphilis, respectively) came to be contracted. By wondering whether or not the illness in question had to happen, Helen and the unnamed "Reader" invite broader consideration of causality and contingency. In the case of "Snows," this inquiry into contingency pertains also to Harry's concerns as to why he failed to write the stories that he might have written.
PDF
![Cucurbit[8]uril-Regulated N...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0935-9648_1521-4095/small "Cucurbit[8]uril-Regulated Nanopatterning of Binary Polymer Brushes via Colloidal Templating")
