Search results for "physics.chem-ph"
showing 10 items of 359 documents
Solution nuclear magnetic resonance spectroscopy on a nanostructured diamond chip
2017
We demonstrate nuclear magnetic resonance (NMR) spectroscopy of picoliter-volume solutions with a nanostructured diamond chip. Using optical interferometric lithography, diamond surfaces were nanostructured with dense, high-aspect-ratio nanogratings, enhancing the surface area by more than a factor of 15 over mm^2 regions of the chip. The nanograting sidewalls were doped with nitrogen-vacancy (NV) centers so that more than 10 million NV centers in a (25 micrometer)^2 laser spot are located close enough to the diamond surface (5 nm) to detect the NMR spectrum of 1 pL of fluid lying within adjacent nanograting grooves. The platform was used to perform 1H and 19F NMR spectroscopy at room tempe…
The heat of transfer in a chemical reaction at equilibrium.
2007
International audience; We study a reacting mixture (2F $ F2) in a temperature gradient. We had previously used boundary-driven non-equilibrium molecular dynamics (NEMD) simulations to study this system, and found that the reaction was close to local chemical equilibrium in temperature gradients up to 1012 K/m. Using the condition of local chemical equilibrium, we show that the heat of transfer of the reacting mixture is equal to minus the enthalpy of the reaction. The fact that the sign of the heat of transfer is determined by the type of reaction adds insight to the discussion of the origin of the sign
Gasless Combustion Regimes Near the Concentration Limits of Extinction
2008
International audience
Liquid–solid interfaces: structure and dynamics from spectroscopy and simulations
2014
Liquid–solid interfaces play an important role in a number of phenomena encountered in biological, chemical and physical processes. Surface-induced changes of the material properties are not only important for the solid support but also for the liquid itself. In particular, it is now well established that water at the interface is substantially different from bulk water, even in the proximity of apparently inert surfaces such as a simple metal. The complex chemistry at liquid–solid interfaces is typically fundamental to heterogeneous catalysis and electrochemistry, and has become especially topical in connection with the search for new materials for energy production. A quite remarkable exa…
The effect of polycations on early cement paste
2010
International audience; This paper studies the possibility for improving the ductility of cement based materials by means of oligocationic additives. Actually, the setting of cement is due to ionic correlation forces between highly negatively charged C-S-H nanoparticles throughout a calcium rich solution. The main drawback of this strong attraction is its very short range that results in low elastic deformation of hydrated cementitious materials. A way to enlarge the attraction range between C-S-H particles would be to add cationic oligomers that would compete with calcium ions modifying the ionic correlation forces via a bridging mechanism of longer range, which could lead to a more ductil…
Water orientation and hydrogen-bond structure at the fluorite/water interface
2016
AbstractWater in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF2/water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water and are responsible for the…
Fission barriers of doubly charged silver clusters
1999
The monomer evaporation energies and fission barriers of doubly charged silver cluster ions in the size range 9≤n≤25 are measured by collision induced dissociation. They are compared to the dissociation energies of singly charged silver clusters. A macroscopic liquid drop model combined with empirical microscopic corrections successfully describes the measured fission barriers.
Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure
2020
Metal nanoparticles are attractive for plasmon-enhanced generation of hot carriers, which may be harnessed in photochemical reactions. In this work, we analyze the coherent femtosecond dynamics of photon absorption, plasmon formation, and subsequent hot-carrier generation through plasmon dephasing using first-principles simulations. We predict the energetic and spatial hot-carrier distributions in small metal nanoparticles and show that the distribution of hot electrons is very sensitive to the local structure. Our results show that surface sites exhibit enhanced hot-electron generation in comparison to the bulk of the nanoparticle. While the details of the distribution depend on particle s…
Raman and nuclear magnetic resonance investigation of alkali metal vapor interaction with alkene-based anti-relaxation coating.
2016
The use of anti-relaxation coatings in alkali vapor cells yields substantial performance improvements by reducing the probability of spin relaxation in wall collisions by several orders of magnitude. Some of the most effective anti-relaxation coating materials are alpha-olefins, which (as in the case of more traditional paraffin coatings) must undergo a curing period after cell manufacturing in order to achieve the desired behavior. Until now, however, it has been unclear what physicochemical processes occur during cell curing, and how they may affect relevant cell properties. We present the results of nondestructive Raman-spectroscopy and magnetic-resonance investigations of the influence …
Polymer brushes with reversibly tunable grafting density.
2021
We propose a novel class of responsive polymer brushes, where the effective grafting density can be controlled by external stimuli. This is achieved by using end-grafted polymer chains that have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly and in a controlled way as a response to changes in environmental parameters. The effect is demonstrated by numeri…