Fine Structure of the Rayleigh Line in Amorphous Substances

As is well known, when monochromatic light scattered by a liquid is examined under high resolution it exhibits a fine structure: an undisplaced central line and two lines on either side with wavelengths slightly different from that of the incident light. The appearance of the displaced components was first predicted by Brillouin1. On the basis of his theory, the observed displacements of frequency are regarded as a Doppler effect arising from the reflexion of the light wave by the progressive sound waves of thermal origin in the scattering medium. The frequency shift of the so-called Brillouin components is given by the formula where nu and c are the velocities of sound and light in the medium and theta is the angle of scattering. That the effect contemplated by Brillouin does arise in liquids and crystals is now a well-established experimental fact.

Activities in liquid Ga-Te alloys at 1120 k

The activity of gallium in liquid Ga-Te alloys has been measured at 1120 K using a solid state galvanic cell incorporating yttria-stabilized thoria as the solid electrolyte. The cell can be schematically represented as (−) W,Re,Ga(1)+Ga2O3(s)|(Y2O3) ThO2|Ga-Te(1) + Ga2O3(s), Re, W (+) The activity of tellurium was derived by Gibbs-Duhem integration. The activity of gallium shows negative deviation from Raoult's law for XGa < 0.6 and positive deviation from ideality for XGa > 0.6. The activity of gallium was constant in the composition range 0.73 < XGa < 0.89, indicating liquid state immiscibility in this region. The Gibbs energy of mixing and the concentration-concentration structure factor at long wavelength limit show a minimum at XGa ≈ 0.4, suggesting strong interactions in the liquid phase with formation of ‘Ga2Te3‘-type complexes

Structure and dynamics of benzene in one-dimensional channels

Molecular dynamics investigation of benzene in one-dimensional channel systems A1PO(4)-5, VPI-5, and carbon nanotube is reported. The results suggest that, in all the three host systems, the plane of benzene is almost perpendicular to the channel axis when the molecule is near the center of the channel and the plane of benzene is parallel to the channel axis when the molecule is near the wall of the channel. The density distribution of benzene as a function of channel length, z and the radial distance, r, from the channel axis is also different in the three host structures. Anisotropy in translational diffusion coefficient, calculated in body-fixed frame of benzene, suggests that benzene prefers to move with its plane parallel to the direction of motion in A1PO(4)-5 and VPI-5 whereas in carbon nanotube the motion occurs predominantly with the plane of the benzene perpendicular to the direction of motion.;Anisotropy associated with the rotational motion is seen to alter significantly in confinement as compared to liquid benzene. In A1PO(4)-5, the rotational anisotropy is reversed as compared to liquid benzene thereby suggesting that anisotropy arising out of molecular geometry can be reduced. Reorientational correlation times for C-6 and C-2 axes Of benzene are reported. Apart from the inertial decay of reorientational correlation function due to free, rotation, two other distinct regimes of decay are observed in narrower channels (AIPO(4)-5 and carbon nanotube): (i) an initial fast decay (0.5-2 ps) and (ii) a slower decay (>2 ps) of reorientational correlation function where C-6 decays slower than C-2 Similar to what is observed in liquid benzene. In the initial fast decay, it is seen that the decay for C-6 is faster than C-2 which is in contrast to what is observed in liquid benzene or for benzene confined in VPI-5.

Molecular theory of solvation and solvation dynamics of a classical ion in a dipolar liquid

A microscopic theory of equilibrium solvation and solvation dynamics of a classical, polar, solute molecule in dipolar solvent is presented. Density functional theory is used to explicitly calculate the polarization structure around a solvated ion. The calculated solvent polarization structure is different from the continuum model prediction in several respects. The value of the polarization at the surface of the ion is less than the continuum value. The solvent polarization also exhibits small oscillations in space near the ion. We show that, under certain approximations, our linear equilibrium theory reduces to the nonlocal electrostatic theory, with the dielectric function (c(k)) of the liquid now wave vector (k) dependent. It is further shown that the nonlocal electrostatic estimate of solvation energy, with a microscopic c(k), is close to the estimate of linearized equilibrium theories of polar liquids. The study of solvation dynamics is based on a generalized Smoluchowski equation with a mean-field force term to take into account the effects of intermolecular interactions. This study incorporates the local distortion of the solvent structure near the ion and also the effects of the translational modes of the solvent molecules.The latter contribution, if significant, can considerably accelerate the relaxation of solvent polarization and can even give rise to a long time decay that agrees with the continuum model prediction. The significance of these results is discussed.

A modified least squares algorithm to treat associations in liquid alloys

The associated model for binary systems has been modified to include volume effects and excess entropy arising from preferential interactions between the associate and the free atoms or between the free atoms. Equations for thermodynamic mixing functions have been derived. An optimization procedure using a modified conjugate gradient method has been used to evaluate the enthalpy and entropy interaction energies, the free energy of dissociation of the complex, its temperature dependance and the size of the associate. An expression for the concentration—concentration structure factor [Scc (0)] has been deduced from the modified associated solution model. The analysis has been applied to the thermodynamic mixing functions of liquid Ga-Te alloys at 1120 K, believed to contain Ga2Te3 associates. It is observed that the modified associated solution model incorporating volume effects and terms for the temperature dependance of interaction energies, describes the thermodynamic properties of Ga-Te system satisfactorily.

Polarization relaxation, dielectric dispersion, and solvation dynamics in dense dipolar liquid

A unified treatment of polarization relaxation, dielectric dispersion and solvation dynamics in a dense, dipolar liquid is presented. It is shown that the information of solvent polarization relaxation that is obtained by macroscopic dielectric dispersion experiments is not sufficient to understand dynamics of solvation of a newly created ion or dipole. In solvation, a significant contribution comes from intermediate wave vector processes which depend critically on the short range (nearest‐neighbor) spatial and orientational order that are present in a dense, dipolar liquid. An analytic expression is obtained for the time dependent solvation energy that depends, in addition to the translational and rotational diffusion coefficients of the liquid, on the ratio of solute–solvent molecular sizes and on the microscopic structure of the polar liquid. Mean spherical approximation (MSA) theory is used to obtain numerical results for polarization relaxation, for wave vector and frequency dependent dielectric function and for time dependent solvation energy. We find that in the absence of translational contribution, the solvation of an ion is, in general, nonexponential. In this case, the short time decay is dominated by the longitudinal relaxation time but the long time decay is dominated by much slower large wave vector processes involving nearest‐neighbor molecules. The presence of a significant translational contribution drastically alters the decay behavior. Now, the long‐time behavior is given by the longitudinal relaxation time constant and the short time dynamics is controlled by the large wave vector processes. Thus, although the continuum model itself is conceptually wrong, a continuum model like result is recovered in the presence of a sizeable translational contribution. The continuum model result is also recovered in the limit of large solute to solvent size ratio. In the opposite limit of small solute size, the decay is markedly nonexponential (if the translational contribution is not very large) and a complete breakdown of the continuum model takes place. The significance of these results is discussed.

Primary structure of belladonna mottle virus coat protein.

The coat protein of belladonna mottle virus (a tymovirus) was cleaved by trypsin and chymotrypsin, and the peptides were separated by high performance liquid chromatography using a combination of gel permeation, reverse phase, and ion pair chromatography. The peptides were sequenced manually using the 4-N, N-dimethylaminoazobenzene-4'-isothiocyanate/phenyl isothiocyanate double-coupling method. The chymotryptic peptides were aligned by overlapping sequences of tryptic peptides and by homology with another tymovirus, eggplant mosaic virus. The belladonna mottle virus is more closely related to eggplant mosaic virus than to turnip yellow mosaic virus, the type member of this group, as evident from the sequence homologies of 57 and 32%, respectively. The accumulation of basic residues at the amino terminus implicated in RNA-protein interactions in many spherical plant viruses was absent in all the three sequences. Interestingly, the amino-terminal region is the least conserved among the tymoviruses. The longest stretch of conserved sequence between belladonna mottle virus and eggplant mosaic virus was residues 34-44, whereas it was residues 96-102 in the case of belladonna mottle virus and turnip yellow mosaic virus. A tetrapeptide in the region (residues 154-157) was found to be common for all the three sequences. It is possible that these conserved regions (residues 34-44, 96-102, 154-157) are involved in either intersubunit or RNA-protein interactions.

Activities, concentration fluctuations and complexing in liquid Ca-Al alloys

Détermination de l'activité du calcium par la méthode d'effusion de Knudsen. Calcul, à partir de la distribution mesurée pour l'aluminium entre l'alliage et du fer pur, de l'activité de l'aluminium dans des alliages riches en calcium. Détermination en combinant les deux méthodes, des activités des deux composants et de l'énergie de Gibbs de mélange pour tout le domaine de composition. Calcul et analyse du facteur de structure concentration-concentration

Preparation and characterization of silane-stabilized, highly uniform, nanobimetallic Pt-Pd particles in solid and liquid matrixes

Highly uniform, stable nanobimetallic dispersions are prepared in a single si ep in the form of sols, gels, and monoliths, using organically modified silicates as the matrix and the stabilizer. The Pt-Pd bimetallic dispersions are characterized by W-vis, TEM, SEM, and XRD measurements. The evolution of silicate was followed by IR spectroscopy. XPS and CO adsorption studies reveal that the structure of the particles consists of a palladium core and a platinum shell. Electrocatalysis of ascorbic acid oxidation has been demonstrated using thin films of silicate containing the nanobimetal particles on a glassy carbon electrode.

Freezing of a colloidal liquid subject to shear flow

A nonequilibrium generalization of the density-functional theory of freezing is proposed to investigate the shear-induced first-order phase transition in colloidal suspensions. It is assumed that the main effect of a steady shear is to break the symmetry of the structure factor of the liquid and that for small shear rate, the phenomenon of a shear-induced order-disorder transition may be viewed as an equilibrium phase transition. The theory predicts that the effective density at which freezing takes place increases with shear rate. The solid (which is assumed to be a bcc lattice) formed upon freezing is distorted and specifically there is less order in one plane compared with the order in the other two perpendicular planes. It is shown that there exists a critical shear rate above which the colloidal liquid does not undergo a transition to an ordered (or partially ordered) state no matter how large the density is. Conversely, above the critical shear rate an initially formed bcc solid always melts into an amorphous or liquidlike state. Several of these predictions are in qualitative agreement with the light-scattering experiments of Ackerson and Clark. The limitations as well as possible extensions of the theory are also discussed.

Liquid Limit Of Kaolinitic Soils

This paper elucidates the relative importance of soil structure and various compositional factors in influencing the liquid limit of natural kaolinitic soils. Earlier studies dealt with purified systems and anticipated that the liquid limit of the soils would increase with percentage clay size fraction and surface area, and that soils with a greater degree of paricle flocculation would possess a higher liquid limit than soils with a more parallel particle arrangement. The results revealed that the inter-particle attraction and repulsion forces have a prominent role in determining the liquid limit of kaolinitic soils. These forces determine the particle arrangement (clay fabric) which in turn regulates the liquid limit values. The influence of clay fabric was ascertained from the relationships of liquid limit with shrinkage limit and sediment volume (in water) values. It was anticipated that kaolinitic soils with a greater degree of particle flocculatin and a higher liquid limit would shrink less and occupy a higher sedimentation volume. As expected an increase in liquid limit was accompanied by an increase in shrinkage limit and sediment volume in water.

Microscopic expression for frequency and wave vector dependent dielectric constant of a dipolar liquid

A microscopic expression for the frequency and wave vector dependent dielectric constant of a dense dipolar liquid is derived starting from the linear response theory. The new expression properly takes into account the effects of the translational modes in the polarization relaxation. The longitudinal and the transverse components of the dielectric constant show vastly different behavior at the intermediate values of the wave vector k. We find that the microscopic structure of the dense liquid plays an important role at intermediate wave vectors. The continuum model description of the dielectric constant, although appropriate at very small values of wave vector, breaks down completely at the intermediate values of k. Numerical results for the longitudinal and the transverse dielectric constants are obtained by using the direct correlation function from the mean‐spherical approximation for dipolar hard spheres. We show that our results are consistent with all the limiting expressions known for the dielectric function of matter.

The structure of phosphacymantrene

Proton NMR spectra of phosphacymantrene (π-phospholyl manganese tricarbonyl) orientated in the nematic phases of liquid crystals have been investigated. The derived H-H and H-P direct dipolar coupling constants have been used to determine the relative proton-proton and proton-phosphorus distances. A comparison of the geometrical data of various 5-membered aromatic heterocycles shows that the relative distances between the protons closest to the heteroatom increase with the van der Waals radius of the heteroatom. The results suggest that NMR spectroscopy of orientated molecules can be used to determine van der Waals radii.

Role of molecular reorientation in the vitrification of molecular liquids: A Monte Carlo study of the liquid and glassy states of 2,2-dimethylbutane

The liquid and the glassy phases of 2,2-dimethylbutane have been investigated by isothermal isobaric ensemble Monte Carlo simulation. Thermodynamic Properties and radial distribution functions for both the liquid and the glass have been obtained. The radial distribution functions have been classified into three types based on the accessibility of the group. It has been shown that the structure of the Iiquid and the glass can be understood in terms of the above classification of the radial distribution functions. Molecular reorientation plays an important role in the structural rearrangement accompanying glass formation. As much as 35% of the contribution to the increase in the intermolecular interaction energy on vitrification is due to the reorientation of the neighbouring pairs of molecules. The observed changes in the dimerisation energy and the bonding energy distribution function are consistent with the observed structural changes.

Dynamic structure factors of a dense mixture

We compute the dynamic structure factors of a dense binary liquid mixture. These describe dynamics on molecular length scales, where structural relaxation is important. We find that the presence of a few large particles in a dense fluid of small particles slows down the dynamics considerably. We also observe a deep narrowing of the spectrum for a disordered mixture composed of a nearly equal packing of the two species. In contrast, a few small particles diffuse easily in the background of a dense fluid of large particles. We expect our results to describe neutron scattering from a dense mixture.