The technique of specular reflection of neutrons has been used to investigate the adsorption of decyltrimethylammonium bromide (DTAB) at the aqueous solution/air interface over the concentration range 0.002-0.1 M. Hydrogen-deuterium substitution in both surfactant and solvent has been used to highlight different features of the adsorbed layer and to distinguish between solvent and solute in this layer. At the lowest concentration the thickness of the adsorbed layer is 16 ± 3 A, indicating that the molecules are aligned with the long axis perpendicular to the interface. At a concentration of 0.05 M, where the monolayer is essentially complete, the thickness is found to be 21 ± 1 A. This suggests that in the more closely packed monolayer the head groups, which carry a positive charge, may be "staggered" in order to minimize their mutual repulsion. A detailed analysis of the structure at 0.05 M indicates that the layer may be divided into two regions: a head group region, 6 A thick, containing the trimethylammonium head group, counterion, water, and about 10% of the alkyl chain tails; and a tail group region, 15 A thick, containing only tail groups. The area per molecule of surfactant at the saturated monolayer is found to be 58 ± 5 A2. Above the critical micelle concentration (0.065 M) the structure of the interface is more complex. The monolayer itself is some 15% more dense than the saturated monolayer formed below the cmc. The shape of the reflectivity profile is shown to be consistent with some ordering of the micelles beneath the surface, separated from the monolayer by a thin layer of water, which contains no surfactant and which has a density more akin to that of water in hydrates. Mixtures of DTAB and sodium decanoate have also been investigated. Equimixtures of the two oppositely charged surfactants are much more strongly adsorbed than either of the two individual components. Even at the low total concentration of 0.01 M the area per surfactant molecule of the mixed monolayer is 36 A2 compared with 73 A2 for 0.01 M DTAB alone.

Following the discovery of a first-order phase transition in annealed KOH-doped ice at 72 K, which was identified as the order–disorder transition associated with the proton positions, a structural study has now been made. Powder neutron diffraction measurements on KOD-doped D2O above and below the phase transition, together with x-ray diffraction measurements, reveal a partial ordering of the hydrogen atoms at low temperatures. The equilibrium structure of ice at low tempertures has orthorhombic symmetry, space group Cmc21, with the same lattice as the high-temperature Ih (P63/mmc) modification. The structure is polar and there is evidence that the ordered domains are less than about 40 Å in dimension.

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Results of numerical calculations of the electrical resistivity of the following primary solidsolution alloys are presented: Cu(Zn), Cu(Ga), Cu(Ge), Ag(Pd), and Ni(Mo). Our theoretical model is one reported earlier by Butler and uses a charge-self-consistent Korringa-Kohn-Rostoker coherent-potential approximation. The calculations are valid for strong as well as weak scattering, and for the first time, vertex corrections are included. Excellent agreement is obtained with experiment for the resistivity. PACS numbers: 72.10.Fk, 71.15.JfWe report here rigorous and realistic ab initio calcurequire the existence of well-defined quasiparticles. lations of the dc residual resistivity of random substi-We believe that the model is valid in the regime where tutional alloys. The calculations do not use adjustable the Boltzmann equation breaks down because energy parameters and they start with only the atomic bands are not defined. The model includes vertex numbers, the alloy concentrations, and the lattice corrections, and it properly treats the momentum maparameters as input. 1 The model is based on the trix elements. In this paper we discuss our results for Korringa-Kohn-Rostoker coherent-potential approxicopper-rich alloys of zinc, gallium, and germanium, mation (KKR-CPA) 2 and the one-electron Kubo forfor silver alloys containing palladium, and for nickel mula. 3 It goes beyond any previous model for deteralloyed with molybdenum. mination of transport properties of random alloys inThe dc electrical conductivity tensor in the onethat it is not limited to weak scattering and does not electron approximation can be written in the Kubo for-' malism as 1where the current operators are * e 9 • * e 9 ei\ * m 9r M m 8r v For a spherical nonoverlapping muffin-tin potential, the imaginary part of the Green's function can be expressed as 4 ImG(r,r',€ + ir\) G{t,x\z)~^XT™Xz)Z?{t mt z)Zl,(x' n ,z)for the complex energy z The point r is in unit cell m while the point r' is in cell n with r = R m + r m , where R m is the vector to the center of cell m (We consider, for simplicity only, one atom per unit cell) Zp(r m ,z) is the wave function of angular momentum L (= /,/x) centered on cell m which is regular at the origin and which satisfies the one-electron Schrodinger equation with the spherical muffin-tin potential and complex energy z The T^ is the scattering-path operator which propagates the electron from site m to site n taking into account scatterings at all possible sites.For a binary alloy of atoms A and 5, the potential site n depends on whether it is occupied by an A or B atom. To represent a real random system, we take a configurational average considering all possible arrangements of the two species on the fixed lattice and for the given concentration. We assume that the arrangements are completely random with no shortrange chemical order. We then carry out the configurational average within the CPA. The scattering-path operator r^ for a given configuration is replaced by T cnm (jfaQ scattering-path operator for the CPA ef...