Physical Properties of Magnetic Fluids and Nanoparticles from Magnetic and Magneto-rheological Measurements

Static magnetization curves and the magnetorheological effect were used to study the microstructural properties (agglomerate formation) of magnetic fluids and the properties of dispersed nanoparticles. Improved techniques for magnetogranulometry analysis and a formula for the magnetoviscous effect were proposed. The area of applicability of some existing models was studied. The density, distribution, and dimension of particles, as well as the thickness of the nonmagnetic layer were accurately determined from magnetic measurements. The Shliomis diameter and the effective anisotropy constant were determined from rheological and magnetorheological measurements using information obtained from magnetization curves. Copyright 2000 Academic Press.     

Investigation of chemical mechanical polishing of zinc oxide thin films

Zinc oxide has become an important material for various applications. Commercially available zinc oxide single crystals and as-grown zinc oxide thin films have high surface roughness which has detrimental effects on the growth of subsequent layers and device performance. A chemical mechanical polishing (CMP) process was developed for the polishing of zinc oxide polycrystalline thin films. Highly smooth surfaces with RMS roughness <6 Å (as compared to the initial roughness of 26 ± 6 Å) were obtained under optimized conditions with removal rates as high as 670 Å/min. Effects of various CMP parameters on removal rate and surface roughness were evaluated. The role of pH on the polishing characteristics was investigated in detail.     

Pharmaceutically active ionic liquids with solids handling, enhanced thermal stability, and fast release

Pharmaceutically active compounds in ionic liquid form immobilized onto mesoporous silica are stable, easily handled solids, with fast and complete release from the carrier material when placed into an aqueous environment. Depending on specific ion-surface interactions, they may also exhibit improved thermal stability when compared to the non-adsorbed compounds.     

Removal of uranyl ions from UO2(NO3)2 solution by means of Chlorella vulgaris and Dunaliella salina algae

This paper deals with a study of the biosorption of UO₂ ²⁺ ions on two green algae: Chlorella vulgaris and Dunaliella salina. By investigating the retention degree versus contact time from Langmuir and Freundlich biosorption isotherms, kinetic investigations and FTIR spectra it was found that the biosorption process was greater for Chlorella vulgaris than for Dunaliella salina. A new kinetics method is proposed to establish the reaction order concerning the biosorption process of uranyl ions on these biomasses.      

Interaction of (hydroxypropyl) cellulose with anionic surfactants in dilute regime

(Hydroxypropyl)cellulose (HPC) dilute aqueous solutions in the presence of sodium cholate (CS), sodium deoxycholate (DC), and sodium dodecylsulphate (SDS) were investigated. The hydrophobicity parameter (I ₁/I ₃) from fluorescence has shown a critical aggregation concentration (CAC) lower than the critical micellar concentration (CMC). One or two breakpoints were observed in the curve conductivity vs surfactant concentration. The thermodynamic parameters of aggregation (, and ) and the degree of counterion dissociation were calculated. Evidences for the secondary aggregation of CS/water system were found. The relative viscosity increases for HPC/bile salt solutions only at high surfactant concentrations, whereas for HPC/SDS, it passes through a maximum. The cloud points of both HPC/bile salt solutions at higher surfactant concentrations reach a temperature plateau value around 324 K, while for HPC/SDS, it exceeds 373 K at low SDS concentrations. Dynamic light scattering has demonstrated that the surfactants bind to HPC already at concentrations lower than CAC.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Comparative analysis of the structure of sterically stabilized ferrofluids on polar carriers by small-angle neutron scattering

Results of experiments on small-angle neutron scattering from ferrofluids on polar carriers (pentanol, water, methyl-ethyl-ketone), with double-layer sterical stabilization of magnetic nanoparticles, are reported. Several types of spatial structural organization are observed. The structure of highly stable pentanol-based samples is similar to that of stable ferrofluids based on organic non-polar carriers (e.g., benzene) with mono-layer covered magnetic nanoparticles. At the same time, the effect of the interparticle interaction on the scattering is stronger in polar ferrofluids because of the structural difference in the surfactant shell. The structure of the studied methyl-ethyl-ketone- and water-based ferrofluids essentially different from the previous case. The formation of large (>100 nm in size) elongated or fractal aggregates, respectively, is detected even in the absence of external magnetic field, which corresponds to weaker stability of these types of ferrofluids. The structure of the fractal aggregates in water-based ferrofluids does not depend on the particle concentration, but it is sensitive to temperature. A temperature increase results in a decrease in their fractal dimension reflecting destruction of the aggregates. In addition, in water-based ferrofluids these aggregates consist of small (radius approximately 10 nm) and temperature-stable primary aggregates.     

Secondary poly(propylene) from used accumulators reused as raw material

A reuse process, as raw material, of secondary poly(propylene) from used accumulators, is presented. The importance of solving the scientific aspects, concerning the influence of residual impurities and those resulted from ageing, on properties of regenerated polymers, in certifying the reliability of reusing the secondary polymers as a raw material, is underlined.