Neutron reflection studies at polymer-polymer interfaces

The application of the neutron reflectivity technique to the study of polymer-polymer interfaces is described and several examples given. The high resolution of the technique allows the details of the interface during early stages of mixing to be resolved for a partially miscible blend. The results are discussed in terms of recent theories.     

Finite aperiodic semigroups with commuting idempotents and generalizations

It is proved that any pseudovariety of finite semigroups generated by inverse semigroups, the subgroups of which lie in some proper pseudovariety of groups, does not contain all aperiodic semigroups with commuting idempotents. In contrast we show that every finite semigroup with commuting idempotents divides a semigroup of partial bijections that shares the same subgroups. Finally, we answer in the negative a question of Almeida as to whether a result of Stiffler characterizing the semidirect product of the pseudovarieties ofR-trivial semigroups and groups applies to any proper pseudovariety of groups.     

A barrier function method for minimax problems

This paper presents an algorithm based on barrier functions for solving semi-infinite minimax problems which arise in an engineering design setting. The algorithm bears a resemblance to some of the current interior penalty function methods used to solve constrained minimization problems. Global convergence is proven, and numerical results are reported which show that the algorithm is exceptionally robust, and that its performance is comparable, while its structure is simpler than that of current first-order minimax algorithms.This research was supported by the National Science Foundation grant ECS-8517362, the Air Force Office Scientific Research grant 86-0116, the California State MICRO program, and the United Kingdom Science and Engineering Research Council.     

Terthienyl and poly-terthienyl ligands as redox-switchable hemilabile ligands for oxidation-state-dependent molecular uptake and release.

Mononuclear, dinuclear, and polymeric Ru(II) complexes formed from terthienylalkylphosphino redox-switchable hemilabile ligands demonstrate that this class of ligand provides electrochemical control over the electronic properties, coordination environments, and reactivities of bound transition metals. Specifically, [CpRuCO(kappa(2)-3'-(2-diphenylphosphinoethyl)-5,5' '-dimethyl-2,2':5',2' '-terthiophene)][B(C(6)H(3)-3,5-(CF(3))(2))(4)] (4a) exhibits a 3 orders of magnitude increase in binding affinity for acetonitrile upon terthienyl-based oxidation. FT-IR spectroelectrochemical experiments on 4a indicate that terthienyl-based oxidation removes electron density from the metal center, equivalent to approximately 11-17% of the electronic change that occurs upon direct oxidation of Ru(II) to Ru(III) in analogous complexes. The spectroelectrochemical responses of 4a were compared to those of dimeric and polymeric analogues of 4a. The spectroelectrochemistry of the dimer is consistent with two sequential, one-electron ligand-based oxidations, compared to only one in 4a. In contrast, the polymer exhibits spectroelectrochemical behavior similar to that of 4a. The polymer spectroelectrochemistry shows changes in the metal center electronic properties between two different states, reflective of two discrete oxidation states of the polymeric ligand backbone. We propose that the polymer backbone does not allow one to vary the electronic properties of the metal center through a continuous range of oxidation states due to charge localization within the metalated films. In an effort to explore the molecular uptake and release properties of 4a and its polymer analogue as a function of ligand oxidation state, the oxidation-state-dependent coordination chemistries of 4a and 4a(+)() with a variety of substrates were examined.     

First inelastic neutron scattering studies on thin free standing polymer films

Glass transition studies in free standing polymer films have revealed values of the transition temperature, T(g), which were substantially reduced below the bulk for sufficiently thin films. Here we report on the preparation of two stacks of free standing polystyrene films: 70 films with a thickness of h approximately 107 nm and 140 films with h approximately 55 nm with equivalent total sample thicknesses of approximately 7.5 microm. We have performed the first measurements on such samples using inelastic neutron scattering, and demonstrate that inelastic neutron scattering experiments, performed on the time-of-flight spectrometer IN6 and the backscattering spectrometer IN16 at the Institut Laue-Langevin, are feasible.     

The precision of determinations of zinc content of food

Seven different types of foodstuff (containing 3-100 ppm Zn) were each analysed for zinc by colorimetry, polarography and atomic-absorption spectroscopy. All the techniques yielded similar values for the zinc content of a given sample, but atomic-absorption spectroscopy had a smaller average coefficient of variation.     

Quasielastic scattering of neutrons from freely jointed polymer chains in dilute solutions

Starting with Kirkwood's Fokker–Planck equation for the polymer configuration-space distribution function and using the Zwanzig–Mori projection operator technique we have calculated the scattering law S_(q,w) for a freely jointed model polymer chain in a dilute solution. When memory effects are neglected, the theory predicts a Lorentzian for S_(q,w) with a halfwidth Ω_(q), which we have determined as a function of the momentum transfer q for all values of q. The results are compared with recent neutron scattering experiments on deuterated polytetrahydrofuran and polystyrene in dilute solution in CS₂. It is found that the observed q dependence of Ω(q) is represented satisfactorily by the present theory with a bond length b of about 6.3 Å for polystyrene and 3.8 Å for polytetrahydrofuran, and a friction coefficient ζ = 4πη0b where η₀ is the viscosity of the solvent.     

dHvA measurements of long range strain effects due to lattice dislocations in copper

Lattice dislocations have been shown to produce a factor of 10³ greater dHvA scattering temperature than an estimate from resistivity. The magnitude of this discrepancy is explained by a first principles phase smearing calculation, and is due to the sensitivity of the quantum oscillations to small angle scattering by the long range strain field. Breaking the cubic symmetry by introducing a forest of edge dislocations allows a test of the sensitivity of previously equivalent neck orbits to the relative orientation with respect to the dislocation lines. Both magnitudes and anisotropy agree with the theory. It is shown how to separate these effects from mosaic structure effects also present in these deformed crystals. In a separate experiment, neutron irradiation was used to produce dislocation loops. Here, the dHvA scattering is observed to be of the same order as resistivity scattering, due to the cancellation of the long range dislocation strain field in the loop geometry.     

The monoid of orientation-preserving mappings on a chain

We introduce new kinds of regular monoids of transformations consisting of mappings which preserve or reverse the orientation of a finite cycle.