Electric field dependence of lower critical phase separation behavior in polymer–polymer mixtures

The electric field dependence of the cloud point temperature of a poly(vinyl methyl ether)–polystyrene mixture has been experimentally measured in a laser light scattering experiment. It is found that the cloud point temperature is depressed linearly with the square of the applied electric field. A thermodynamic derivation of the electric field dependence of the spinodal temperature for polymer–polymer mixtures is also presented. A large disagreement between the experimental and theoretical findings is noted and possible explanations for this discrepancy are discussed.     

Interaction between light and crystallizing polymer: a simulation study

A study of light transmission through a crystallizing polymer has been carried out by graphic simulations, consisting of sporadic and pre-determinate nucleation and growth of disks (spherulites) in a rectangular area. Interaction between a light beam crossing a sample of polymer has been described by a series of simple graphical rules, accounting for both absorption and scattering. Results of the code well reproduce the experimental behavior observed in the literature of main beam light intensity emerging from a crystallizing polymer sample and allows a better understanding of the interaction between light and nucleating/growing units. Emerging light behavior calculated by the simulation has been adopted as the basis to suggest the dependence of the light scattering coefficient upon crystallization kinetic parameters.     

State of Water in Hydration Spheres of Potassium Iodide

Ion hydration has been studied for potassium iodide solutions with concentrations from 0 to 51 wt.% at temperatures from 288.15 to 308.15 K based on ultrasonic measurements and molar adiabatic compressibility data. For hydration complexes, structural characteristics have been determined. The structure of noncoordinated water plays a significant role even in concentrated solutions. An electrostatic ion field has a strong effect on the temperature dependence of the molar volume of hydration water. A method for the precise determination of the total solvation boundary is presented.     

Small-angle light scattering from thin polymer films: Multiple scattering from Debye–Bueche scatterers

An extension of Hartel's theory for multiple scattering has been applied to the case of small-angle light scattering from polymer films with random two-phase morphology. The scattering is treated in terms of Debye–Bueche theory from which values of the correlation length, an average phase size, and mean-square fluctuation in polarizability are determined. It is shown that multiple scattering leads to a reduction in the angular dependence of scattering due to an enhancement of scattering at high angles. This leads to an underestimate of the correlation length and an overestimate of the magnitude of the mean-square polarizability fluctuation.     

A laser diffraction study of amphiphilic cholesteric liquid crystals prepared from potassium dodecanoyl l-serinate

Amphiphilic cholesteric liquid crystal samples have been prepared using potassium dodecanoyl l-serinate (lKDDS). Laser diffraction was used to determine the twist of the helix in these samples. Detergent concentration and the temperature dependence of the twist have been investigated. The results were found to be similar to those using the detergent potassium dodecanoyl l-alaninate (lKDDA). A binary cholesterogen study has been made using both the detergents lKDDS and lKDDA. The twist was not enhanced and the inter-cholesterogen (detergent) interaction was shown not to be present in these micellar mixtures.     

Multiple scattering of light from polymer dispersed liquid crystal material

Light scattering from polymer dispersed liquid crystal (PDLC) material has been studied experimentally and by Monte Carlo simulation. Light scattering was measured as a function of both scattering angle and cell thickness. The cell thicknesses of practical interest are in an intermediate regime where neither single scattering nor light diffusion applies. Both the angular and the thickness dependence of the scattering intensity can be described accurately by a Monte Carlo simulation of multiple scattering from a homogeneous distribution of independent scatterers. The model smoothly interpolates between the single scattering limit for thin cells and the diffusion limit for thick cells. It can easily be extended to include any specific feature of a scattering display system.     

The N2Ar potential energy surface

The potential energy surface for the N₂Ar system has been obtained assuming a spherical average interaction previously reported from this laboratory. The angular dependence has been assessed by a combined analysis of the integral and differential scattering cross sections and sonic spectroscope data. The potential energy surface is given via a parametric model. A similar potential energy surface for O₂Ar has been obtained with the same procedure. This surface is an improvement of an earlier one, because it reproduces the differential total cross sections recently measured.     

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.     

Extraction of trivalent lanthanum,cerium and yttrium thiocynate complexes by tributyl phosphate

The distribution of La(III), Ce(III) and Y(III) from potassium thiocyanate solutions by tributyl phosphate is described. The dependence of extraction on pH, thiocyanate concentration, metal and extractant concentration, diluent type and temperature, was thoroughly investigated. Solvation numbers and thermodynamic data were calculated and discussed. A method has been suggested for the separation of Th(IV) from such elements.     

Extraction of beryllium(II) from iodide solutions by tributyl phosphate

The distribution of beryllium between aqueous sulfuric acid/potassium iodide solutions and organic phases of tributyl phosphate is described. The dependence of extraction on the pH of the aqueous phase, metal and extractant concentration, diluent type and organic additive, has been investigated. Extraction mechanism is discussed on the basis of results obtained. A method for the separation and determination of beryllium, in a mixture of beryllium and aluminium (with other contaminants) is outlined.     

Time dependence of the resonant and near resonant photon moleculaar interactions

Using scattering theory we have derived an explicit expression for the time dependence of the resonant interaction of lorentzian photons with molecular systems. A discussion is presented on the dependence of molecular states on the nature of the exciting photon with an additional regard for the appropriate choice of basis sets. By examining the time dependence of the scattered photon a clear resonance Raman scattering resonance fluorecence limit emerges based on the temporal relationship of the scattered photon to that of the resonant state and incident photon. The influence on the resonant scattering of random fluctuation and relaxation processes that lead to dissipation is discussed with reference to scattering experiments performed in the gas and condensed phases.     

Quantum dynamics of dissociative adsorption of H_2 on Ni(100) using the dynamical Lie algebraic method

A dynamical Lie algebraic method has been applied to treating the quantum dynamics of dissociative adsorption of H_2 on a static flat metal surface. An LEPS potential energy surface has been used to describe the interaction of H_2 with Ni(100) surface. The dependence of the initial state-selected dissociation probability was obtained analytically on the initial kinetic energy and time. A comparison with other theoretical calculations and experiments is made. The results show that the method can be effectively used to describe the dynamics of reactive gas-surface scattering.     

Scattering of light from oriented polymer films. II

A statistical theory for the scattering of light from oriented polymer films is developed in terms of angularly dependent generalized correlation functions. Numerical calculations of scattering patterns are carried out for special cases. The scattering depends upon two types of distributions describing (1) the orientation distribution of optical axes of scattering elements and (2) the angular dependence of correlation in orientation between pairs of optic axes. These distributions are expanded in Fourier series (in a two-dimensional treatment), the coefficients of which are functions of elongation and describe the elongation dependence of the scattering patterns.     

LIGHT SCATTERING SPECTROPHOTOMETRY FROM ISOLATED CONTROL AND TRIAZOLE-TREATED CHLOROPLASTS

Light scattering relaxation spectrophotometry has proven to be a useful technique to monitor rapid cytophysical changes in chloroplast suspensions brought about by flash illumination. This paper compares the Mg-ATP dependent light scattering behaviour of cholorplasts isolated from control and triazole-treated wheat seedlings. Our results suggest that triazole-treatment enhances Mg-ATP dependent activity. This same enhancement in control chloroplasts can be brought about by introducing potassium ion in the presence of valinomycin. Therefore, the potassium ion might account for part of the stress resistance conferred by triazole treatment.     

A new ab initio potential energy surface for studying vibrational relaxation in NO(v) + NO collisions

A new ab initio potential energy surface for the ground state of the NO-NO system has been calculated within a reduced dimensionality model. We find an unusually large vibrational dependence of the interaction potential which explains previous spectroscopic observations. The potential can be used to model vibrational energy transfer, and here we perform quantum scattering calculations of the vibrational relaxation of NO(v). We show that the vibrational relaxation for v = 1 is 4 orders of magnitude larger than that for the related O(2)(v) + O(2) system without having to invoke nonadiabatic mechanisms as had been suggested in the past. For highly vibrationally excited states, we predict a strong dependence of the rates on the vibrational quantum number as has been observed experimentally, although there remain important quantitative differences. The importance of a chemically bound isomer on the relaxation mechanism is analyzed, and we conclude it does not play a role for the values of v considered in the experiment. Finally, the intriguing negative temperature dependence of the vibrational relaxation rate constants observed in experiments was studied using an statistical model to include the presence of many asymptotically degenerate spin-orbit states.     

A photoelectrochemical study of anodic oxides on lead selenide surfaces in alkaline solutions

Lead selenide is a narrow gap semiconductor material. It finds applications in infrared emitting and detecting devices. Their performance is closely related to charge carrier recombination at the surface, which can be reduced by passivation, e.g. due to PbSeO₃ formation by anodic oxidation in alkaline solutions. In dependence on the pretreatment of the surface, two different types of oxide formation were observed. To determine the electronic properties of the anodic oxide, the wavelength dependence of the photocurrent was investigated. The energy of the band gap of both types of anodic oxide on PbSe has been determined to be 2.4 eV for the direct and 1.8 eV for the indirect band gap. A weakening of the photocurrent generated in the bulk (PbSe) due to scattering or absorption within the oxide confirms the potential dependence of the oxide thickness for a high field growth mechanism.     

Scattering of a potassium atom beam from potassium promoted catalyst surfaces via electronically excited clusters

Surface scattering of potassium atom beams is observed from surfaces of a potassium promoted catalyst, which is known to emit Rydberg K* species and clusters K _n ^* . The surfaces studied are cut flat from pellets of an industrial catalyst, the promoted iron oxide catalyst for styrene production. The scattering is studied in the temperature range 500–1000 K in an UHV apparatus with a K atom beam at 45° towards the normal, with surface ionization and ion detection over an angular range of ?90° to +90° with respect to the surface normal. Bilobular scattering patterns are observed, which are mainly back-scattering at low temperatures, below 750 K. A large signal due to ions emitted in the backwards direction is also found with a voltage on the sample. This back-scattering indicates that the scatterers are heavy clusters outside the surface. The ion formation in the backwards direction is proposed to be due to collisions with electronically excited clusters K _n ^* of the type recently observed by field ionization detection (Kotarba et al. 1994). The bilobular scattering transforms into asymmetric patterns with a larger forward (specular) lobe at higher temperatures, above 800 K. Only a small fraction of the beam molecules is scattered off the surface. The scattering is well described by inelastic surface scattering theory. This shows that the actual scattering surface is rather flat, which is proposed to be due to an antibonding Rydberg type interaction, of long range (hundreds of Å), between the impinging excited K atom and the surface. The temperature dependence of the neutral scattering gives a barrier of 0.96 eV, close to what is generally found for Rydberg species emission from such surfaces. At larger K surface densities, the contributions to the peaks from the beam flux is shown to agree with this picture involving collisions with excited clusters outside the surface.     

Theory of the time and frequency dependence of near-resonant raman scattering and quantum beats

A calculation of the time dependence of light scattering from an atom or molecules yields a continuous transition from fast Raman scattering to resonance fluorescence in agreement with recent experiments. If the resonant excited state has two or more nearby levels, “quantum beats” may be observed. These quantum beats are present even if the incident light is tuned off resonance.     

Inelastic scattering of vibrationally excited KBr BY Ar and CO2

Scattering of highly vibrationally excited potassium bromide by argon and carbon dioxide has been investigated. Velocity resolved KBr scattering intensities indicate that highly translationally inelastic collisions occur in both systems and, in the CO₂ system, show effects due to VT, VV competition.