Micromagnetic investigation of sub-1 0 0-nm magnetic domains in atomically stacked Fe(0 0 1)/Au(0 0 1) multilayers

Continuous films and nanostructures of atomically stacked epitaxial Fe(0 0 1)/Au(0 0 1) multilayers have been studied by soft X-ray and Lorentz microscopy as well as micromagnetic simulations. Domain imaging shows about 65 nm wide magnetic stripe domains, in which the magnetization is oriented perpendicular to the film plane. These results are confirmed by micromagnetic simulations, which also yield additional information about the internal structure of domains and walls.     

Block copolymers of ethylene oxide and phenyl glycidyl ether: micellization, gelation, and drug solubilization

Three triblock copolymers of ethylene oxide and phenyl glycidyl ether, type E(m)G(n)E(m), where G = OCH2CH(CH2OC6H5) and E = OCH2CH2, were synthesized and characterized by gel-permeation chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and NMR spectroscopy. Their association properties in aqueous solution were investigated by surface tensiometry and light scattering, yielding values of the critical micelle concentration (cmc), the hydrodynamic radius, and the association number. Gel boundaries in concentrated micellar solution were investigated by tube inversion, and for one copolymer, the temperature and frequency dependence of the dynamic moduli served to confirm and extend the phase diagram and to highlight gel properties. Small-angle X-ray scattering was used to investigate gel structure. The overall aim of the work was to define a block copolymer micellar system with better solubilization capacity for poorly soluble aromatic drugs than had been achieved so far by use of block copoly(oxyalkylene)s. Judged by the solubilization of griseofulvin in aqueous solutions of the E(m)G(n)E(m) copolymers, this aim was achieved.     

The effects of ageing by ultraviolet degradation of recycled polyolefin blends

Products manufactured from recycled polyolefin blends were subjected to accelerate weathering conditions and subsequent tests. Field-aged products were also tested.Samples were analysed for changes in mechanical, rheological and chemical properties. Data obtained in this study, by means of tensile, impact, and melt flow tests, GPC, gloss and colour analyses showed that the effect of UV exposure, whether in the field or artificial environments, was not significant as far as the mechanical properties of the materials were concerned. There was some change in the surface characteristics but such surface effects would not compromise the mechanical integrity of the product when recycled. During reprocessing of the materials, it is likely that stabilizer is redistributed at the surface of any new moulding, thus renewing the surface characteristics. Hence damaged or end-of-life products need not be discounted from recycling.     

Evaluation of solute distribution coefficients in solubilized systems

A theoretical treatment is proposed for the determination of the distribution characteristics of a solubilizate between micellar and aqueous phases from the variation of the critical micelle concentration (CMC) with the molar ratio of components in the system. The theory has been tested by determining the distribution coefficient and free energy of solubilization of n-butanol in the n-butanol/sodium dodecyl sulphate/water system from CMC values determined by conductimetric techniques.     

Influence of the structure of the hydrophobe on the ideality of mixing in micelles in binary mixtures of amphiphilic tricyclic drugs

The composition of the micelles in binary mixtures of the cationic amphiphilic antidepressant drugs nortriptyline, amitriptyline, and doxepin has been determined from an analysis of the variation of the critical micelle concentration from conductivity measurements, as a function of solution composition. Assessment of the nonideality of mixing in terms of the interaction parameter from the regular solution approximation showed small deviations from ideal mixing, with negative interaction parameters for nortriptyline/amitriptyline systems and positive interaction parameters for mixtures of nortriptyline and doxepin. These differences in nonideality have been attributed to differences in the packing of the drugs in the mixed micelles arising from differences in the structure of the hydrophobe.     

Micelles and gels of mixed triblock copoly(oxyalkylene)s in aqueous solution

The micellization in dilute aqueous solution of a 50/50 wt% mixture of two triblock copolymers, E45B14E45 and E62P39E62, and the gelation of concentrated micellar solutions have been investigated over a range of temperatures. Here E, B, and P denote oxyethylene, oxubutylene, and oxypropylene chain units. Comparison is made with aqueous solutions of the individual copolymers. The results of light scattering measurements are consistent with effectively separate micellization of the two copolymers in the mixture. Hard gel formed when the extent of micellization was high for both copolymers. Because of the relatively high critical micellization temperatures of copolymer E62P39E62, the low-temperature boundary of the hard gel was high for this copolymer and for the mixture. The minimum concentration for hard-gel formation was higher for the mixture than for either of the individual copolymers, as would be expected for packing of two distributions of micelles of different average size.     

Self-association of n -hexyltrimethyl-ammonium bromide in aqueous electrolyte solution

 The self-association of n-hexyltrimethylammonium bromide (C₆TAB) in aqueous solution has been studied by static and dynamic light scattering and NMR spectroscopy at 25 °C in the presence of added electrolyte, and critical aggregation concentrations, aggregation numbers and the degree of ionization have been calculated. Aggregation numbers determined from light scattering and from the application of mass-action theory to the concentration dependence of ¹H NMR chemical shifts of four protons along the alkyl chain of C₆TAB, were between three and four over the range of electrolyte concentration studied (0.2–0.7  molkg⁻¹ NaBr). A structure for the small aggregates has been proposed from the NMR chemical shift data. Received: 4 June 2001 Accepted: 17 September 2001     

High temperature adsorption of CO<Subscript>2</Subscript> on various hydrotalcite-like compounds

A study was conducted to describe and quantify how substitution of the divalent cation and interlayer charge compensating anions affect the CO₂ adsorptive capacity of various hydrotalcite-like compounds (HTlcs). Physical and chemical properties of the HTlcs were evaluated using a number of methods and the CO₂ adsorption rate and capacity were measured at elevated temperature (603 K). The results showed that the synthetic analogue of the naturally occurring hydrotalcite mineral, [Mg_0.73Al_0.27(OH)₂](CO₃)_0.13⋅xH₂O, had the best overall adsorption capacity and kinetics. The stability of the adsorption capacity was tested by subjecting the model HTlc to 10 equilibrium adsorption and desorption cycles. At the end of the cycle, the HTlc had maintained approximately sixty-five percent of its initial capacity. Temperature programmed desorption of CO₂ was used to quantify the surface basicity of the various HTlcs. The results showed that the reversible physisorption portion of the CO₂ isotherm was correlated to the number of surface basic sites on the HTlcs.     

The chromonic phases of dyes

Abstract

It has been shown that the lyotropic liquid-crystalline phases formed by certain dyes are structurally analogous to the chromonic N and M liquid-crystalline phases previously thought to be unique to certain anti-asthmatic/anti-allergic drugs. We suspect that these two groups of compounds will prove to be representatives of a large new class of mesogenic materials.