Studies on microemulsions

The microemulsions formed in the 4-component system water-potassium oleate-hexanol-dodecane have been investigated by time-average light scattering and small angle neutron scattering. A constant volume fraction ratio water: potassium oleate of 1.44 was used and at this constant composition, which gave a pseudo 3-component system, a wide region of the microemulsion domain was examined. In order to interpret the scattering data at finite volume fractions of the dispersed phase, water, allowance had to be made for interactions between the water-in-oil microemulsion droplets. This was carried out using a hard sphere model for the interaction. It is shown that using this model self-consistent results are obtained by light scattering and neutron scattering and an estimate can be made of the size of the particles in concentrated colloidal dispersions.     

Proton dynamics in an extended array of hydrogen bonds: normal coordinates, proton transfer and macroscopic quantum entanglement in the ground state

After a brief introduction to neutron scattering techniques, illustrated with the scattering function for harmonic oscillators, some new aspects of proton dynamics in the KHCO₃ crystal are presented. The full scattering function for the proton modes measured on single crystals provides a graphic view of proton dynamics. Vibrational states are fully characterized with three quantum numbers. The effective oscillator mass of 1 amu confirms the decoupling of protons from the lattice. Combining infrared, Raman and inelastic neutron scattering techniques, the double minimum potential for the transfer of a single proton along hydrogen bonds is totally determined. Elastic neutron scattering techniques probe dynamics in the fully degenerate ground state. Quantum entanglement arising from normal coordinates gives rise to quantum interference. With diffraction techniques, the dynamical structure arising from large-scale quantum coherence is observed as ridges of intensity, well separated from Bragg's peaks. The vibrational wave function in the ground state must be regarded as a superposition of non-factorable macroscopic wave function.     

Attractive interactions in critical scattering from non-ionic micelles

We have studied the temperature-dependent critical scattering of both light and neutrons from aqueous solutions ofn-octyl pentaoxyethylene glycol monoether (C₈E₅). We show that the assumption of a short-ranged temperature-dependent attractive pair potential between approximately spherical micelles of constant size permits a quantitative analysis of the neutron scattering data. The analysis, which is undertaken using current liquid-state theory and is in analytic form, contains only one free parameter, the depth of the attractive potential. We find that a potential with a range of only a fraction of a nm is sufficient to generate spatial correlations over tens of nm as the attractive potential deepens on approaching the critical temperature. The analysis also provides a semi-quantitative understanding of the light scattering data as a function of concentration and temperature, and leads to a qualitative prediction of the form of the phase diagram. Numerical values obtained are consistent with the hypothesis that the primary effect of raising the temperature is to lower the degree of structure of water near the micelle surface, allowing increased van der Waals attraction due to closer contact.     

New developments in theory of fast electron scattering in solids: Applications to microbeam analysis

The study of fast electron interaction with solids in the energy range from 100 eV to several tens of keV is prompted by quickly developing microbeam analysis techniques such as electron probe microanalysis, scanning electron microscopy, electron energy loss spectroscopy and so on. It turned out that for random solids the electron transport problem might be solved on the basis of the generalized radiative field similarity principle. The latter states that the exact differential elastic cross section in the kinetic equation may be replaced by an approximate one provided the conditions of radiative field similarity are fulfilled. Application of the generalized similarity principle to electron scattering in solids has revealed many interesting features of electron transport. Easy to use and effective formulae have been obtained for the angular and energy distribution of electrons leaving a target, total yields of characteristic photons and slow electrons escaping from a sample bombarded by fast primaries, escape probability of Auger electrons as a function of depth etc. The analytical results have been compared with Monte Carlo calculations and experiments in a broad range of electron energies and scattering properties of solids and good agreement has been observed.     

Interpretation of the hydrogen anomaly in neutron and electron compton scattering

In Compton scattering with neutrons in the energy range 20–120 eV, it has been observed that the relative H/M cross sections in a variety of H‐containing materials are 20–40% lower than expected from the composition ratio H/M (M being a heavier element in the same compound). The same phenomenon has also been observed in Compton scattering with electrons of 2 and 20 keV energy. There is, at present, no consensus about the reason for these anomalies. In this theory, they are explained as a result of interference when the scattering particle interacts with more than one hydrogen nucleus. The coherence volume of the actual setup, which limits the number of interfering particles, is therefore an important parameter. It is shown here that the large zero‐point motion of the hydrogen nuclei leads to reductions in the scattering intensity from interfering pairs. Coherence is preserved over the sub‐fs scattering times relevant for this process, even in the condensed systems studied. It is gradually lost when the scattering time is increased, which happens when the neutron energy is reduced (as reflected in lower anomalies for smaller scattering angles). Explicit expressions for the decoherence effect are presented and compared with experimental observation for a selection of observed H‐ and D‐containing systems. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Molecular adsorption onto metallic quantum wires.

We have studied the adsorption of mercaptopropionic acid, 2,2'-bipyridine, and dopamine onto electrochemically fabricated Cu nanowires. The nanowires are atomically thin with conductance quantized near integer multiples of 2e(2)/h. Upon molecular adsorption, the quantized conductance decreases to a fractional value, due to the scattering of the conduction electrons by the adsorbates. The decrease is as high as 50% for the thinnest nanowires whose conductance is at the lowest quantum step, and smaller for thicker nanowires with conductance at higher quantum steps. The adsorbate-induced conductance changes depend on the binding strengths of the molecules to the nanowires, which are in the order of mercaptopropionic acid, 2,2'-bipyridine, and dopamine, from strongest to weakest. The sensitive dependence of the quantized conductance on molecular adsorption may be used for molecular detection.     

A study of measured neutron elastic differential neutron cross sections for 23Na

Elastic neutron scattering angular distributions from ²³Na have been measured for incident neutron energies between 1.0 and 4.0 MeV at the University of Kentucky Accelerator Laboratory using neutron time-of-flight techniques for the scattered neutrons. This is an energy region in which existing data are very sparse. Measurements are compared with the predictions of the light particle-induced reaction code TALYS. The calculations reproduce forward angle scattering but have difficulty with relative minima in the differential cross section and large-angle scattering.     

Proton quantum coherence observed in water confined in silica nanopores

Deep inelastic neutron scattering measurements of water confined in nanoporous xerogel powders, with average pore diameters of 24 and 82 A, have been carried out for pore fillings ranging from 76% to nearly full coverage. DINS measurements provide direct information on the momentum distribution n(p) of protons, probing the local structure of the molecular system. The observed scattering is interpreted within the framework of the impulse approximation and the longitudinal momentum distribution determined using a model independent approach. The results show that the proton momentum distribution is highly non-Gaussian. A bimodal distribution appears in the 24 A pore, indicating coherent motion of the proton over distances d of approximately 0.3 A. The proton mean kinetic energy W of the confined water molecule is determined from the second moment of n(p). The W values, higher than in bulk water, are ascribed to changes of the proton dynamics induced by the interaction between interfacial water and the confining surface.     

Quantized Hamilton Dynamics

The paper describes the quantized Hamilton dynamics (QHD) approach that extends classical Hamiltonian dynamics and captures quantum effects, such as zero point energy, tunneling, decoherence, branching, and state-specific dynamics. The approximations are made by closures of the hierarchy of Heisenberg equations for quantum observables with the higher order observables decomposed into products of the lower order ones. The technique is applied to the vibrational energy exchange in a water molecule, the tunneling escape from a metastable state, the double-slit interference, the population transfer, dephasing and vibrational coherence transfer in a two-level system coupled to a phonon, and the scattering of a light particle off a surface phonon, where QHD is coupled to quantum mechanics in the Schrödinger representation. Generation of thermal ensembles in the extended space of QHD variables is discussed. QHD reduces to classical mechanics at the first order, closely resembles classical mechanics at the higher orders, and requires little computational effort, providing an efficient tool for treatment of the quantum effects in large systems.     

Quantumness of correlations and Maxwell's demon in molecular excitations created by neutron scattering

Nonclassical correlations known as entanglement, quantum discord, quantum deficit, measurement‐induced disturbance, quantum Maxwell's demon, etc., may provide novel insights into quantum‐information processing, quantum‐thermodynamics processes, open‐system dynamics, quantum molecular dynamics, and general quantum chemistry. We study a new effect of quantumness of correlations accompanying collision of two distinguishable quantum systems A and B, the latter being part of a larger (interacting) system B + D. In contrast to the common assumption of a classical environment or “demon” D, the quantum case exhibits striking new qualitative features. Here, in the context of incoherent inelastic neutron scattering from H‐atoms which create molecular excitations (vibration, rotation, translation), we report theoretical and experimental evidence of a new phenomenon: a considerably reduced effective mass of H, or equivalently, an anomalous momentum‐transfer deficit in the neutron‐H collision. These findings contradict conventional theoretical expectations even qualitatively, but find a straightforward interpretation in the new theoretical frame under consideration. © 2015 Wiley Periodicals, Inc.     

The structure of liquid water at room temperature

Full details are given of a recent time-of-flight neutron diffraction experiment in which partial pair correlation functions for liquid water are extracted by isotope substitution. Measurements of differential cross sections of mixtures of heavy and light water are made, and by performing the experiment at the high neutron energies available at a pulsed neutron source (Los Alamos) the magnitude of dynamic corrections to the data is reduced. The problematic hydrogen incoherent scattering is removed by a subtraction technique which avoids reference to dynamic models of the liquid. The results, although they show good agreement with computer simulations, show serious qualitative differences with other neutron experiments on water, and it is suggested these discrepancies are a result of lack of attention to the unusual properties of hydrogen as a scatterer of neutrons.     

Characterization of polymer materials by scattering techniques,with applications to block copolymers

The application of six techniques—static and dynamic light scattering, small-angle neutron and X-ray scattering, neutron and X-ray reflectivity—to the characterization of polymer materials is summarized. Emphasis is placed on the similarities and differences among the various techniques, and on recent advances in experimental practice. Twelve examples from the recent literature are described, most of which concern block copolymers. A brief introduction to block copolymer properties is also provided.     

康普顿散射法测定溶液浓度

基于光子与物质相互作用的康普顿散射效应,利用康普顿散射光子数与散射体的电子密度成正比的原理,提出了用康普顿散射测定溶液浓度的方法,描述了相应的试验装置和测定溶液浓度的步骤,并用此方法测定了氢氧化钠和氯化钾溶液的浓度,分析了引起误差的原因。试验结果表明,用所提出的方法测定溶液的浓度是可行的。     

Compton profiles for ejected electrons: Determination of momentum densities

Electron Compton scattering effects usually lead to the determination of momentum densities in atoms and molecules by cross-section measurements on scattered electrons. Similar information is also shown to be directly available from the study of ejected electrons. The proposed treatment results from a simple alteration of the impulse assumptions and appears to give a satisfactory representation of ejected profiles for medium and high energy electron scattering. Preliminary investigations are discussed here for hydrogen and helium atoms.