George W. Brady

Neutron Inelastic Scattering and X‐Ray Studies of Aqueous Solutions of Dimethylsulphoxide and Dimethylsulphone

Molecular vibrations in solid and liquid dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO2) have been measured by neutron inelastic scattering between 900–8 cm−1. Neutron spectra of the intermolecular frequencies of water molecules in aqueous solutions of perdeuterated DMSO and DMSO2 have also been measured to determine, as a function of concentration and of temperature, the influence of these compounds on the water structure. In addition, the broadening of the incident energy distribution by diffusive motions of H2O molecules has also been investigated. The similarity of intermolecular frequencies in the spectra of both the liquid and solid phases of the pure compounds shows a high degree of dipole association. In dilute aqueous solutions the DMSO and DMSO2 (hydrogenous and perdeuterated) both cause a similar enhancement and sharpening of the intermolecular frequencies of the water structure associated with a small and cooperative perturbation in the orientation of many H2O molecules. This is consist...

Structure of Sodium Metaphosphate Glass

The x‐ray diffraction pattern of sodium metaphosphate glass (formula NaPO3) has been determined. The radial distribution function determined from the diffraction pattern indicates that the structure consists of long chains of PO4 tetrahedra crosslinked to other chains by O–Na–O— bonds. This model agrees with the one advanced by other workers who applied high polymer techniques to the study of metaphosphates.

Cluster Formation in Perfluoroheptane‐i‐Octane Systems near the Consolute Temperature

Small‐angle x‐ray measurements on the system C7F16‐i‐C8H18 at temperatures near the consolute temperature show that a large degree of clustering takes place. Starting with pure i‐C8H18, which exhibits no scattering, the scattered intensity increases with increasing C7F16 concentration in a manner which indicates that the clusters are increasing in size. The maximum size is attained at a volume fraction of ∼0.50, at which point the clusters are made up of ∼140 C7F16 molecules. With a further increase in concentration, interaction peaks first appear in the intensity curves, indicating an approach to close packing, and then the slope of the curves begins to decrease, indicating that a phase reversal has taken place giving rise to smaller clusters of hydrocarbon in perfluorocarbon.

Structure Studies of Solutions of Large Organic Molecules. I. C9H19I and C18H36I2 in Decalin

The x‐ray scattering from solutions of C9H19I and C18H36I2 in decalin, C10H18, at various concentrations has been studied. The principal aim of the research was to develop a technique for the direct determination of end‐to‐end distances of polymers in solution. This was achieved, and the method is outlined in detail. In the course of the work some interesting clustering phenomena were discovered in the monoiodide solutions. A model is proposed which has as its main feature the formation of quasi‐liquid‐crystal regions, with the alkane chains lying parallel to each other and the I atoms in contact.

Structure Studies of Solutions of Large Organic Molecules. II. End‐to‐End Distances of Alkanes from C8− to C22−

End‐to‐end distances for a series of alkanes in the range C8− to C22− have been measured by the technique described in the preceding article. There appears to be good agreement with the theoretical values of the characteristic ratio 〈r2〉 / nl2 cited by Flory. However, there is evidence that solvent effects are present. These are discussed.

Structure Studies of Solutions of Large Organic Molecules. III. Liquid Crystallike Arrangement of Dissolved Long Chain Molecules

An x‐ray diffraction study has been made of the effect of chain length on the configuration of dissolved long chain molecules. In solutions of alkane monoiodides of nearly equal length, the molecules line up such that the interiodine distance is roughly equal to the sum of the chain lengths. When the lengths are quite disparate, the longer chains order preferentially, as manifested by a gross x‐ray spacing of about twice the longest chain length. The morphology and concentration persistence of the solute aggregates are discussed and it is concluded that these latter are in quasiliquid crystal form.

Effect of length on the interaction of dissolved long chain molecules

The results of a study of superstructure formation in long chain alkane solutes are presented. It is found that there is little tendency towards chain aggregation until a chain length of eight atoms (C8−) is reached. A mechanism involving a swivel action around the attracting end group is postulated.

On Small‐Angle Critical Scattering

Recent theoretical studies of simplified models of cooperative assemblies of atoms or molecules suggest that the pair correlation function G(r) at the critical is not given by the Ornstein—Zernike (O.Z.) expression but that this relation becomes asymptotically valid for large distances r away from the critical. Based on some further heuristic considerations we suggest that the low‐angle scattering of radiation or particles from real three‐dimensional cooperative assemblies at the critical composition and temperatures, above but near the critical is essentially given by the Fourier transform of a G(r) which is an interpolation between the O.Z. expression and the critical G(r) suggested by the simplified models. We derive thus the form of the relative, reduced small angle scattering intensity and indicate in what ways departures from the O.Z. predictions are expected and comment on their magnitude. These calculations may possibly explain certain small but systematic anomalies observed in small angle x‐ray s...

Superstructure in dissolved long chains

A series of experiments on solutions of long (C20H41I) and short (C2H5I) chain molecules has verified that the longer molecules form a host micelle for the shorter ones, which appear to interpenetrate the ordered C20− molecules to give an aggregate of similar external morphology. Further measurements on the two systems resulted in a technique to evaluate the contributions of close order I–I, C–C, and C–I terms in the intensity, and from this analysis the I–I superstructure scattering function could be isolated from the rest of the scattering. The scattering function fitted that of a hollow sphere of radius 17 A, as predicted from earlier experiments.

Determination of the Radial Distribution Function and the Direct Correlation Function of Spheres by X‐Ray Small‐Angle Scattering

An experimental determination of the pair and direct correlation functions of polystyrene latex spheres in the high‐density limit has been made. From these the pair potential for hard spheres has been calculated. The significance of the functions as they bear on the Percus—Vevick and the hypernetted chain approximation is discussed.