A magnetic rod interfacial shear rheometer was used to measure the properties of β-casein adsorbed at the air/solution interface as a function of aging time. Over a wide range of concentrations (1 × 10-6 to 2 × 10-2 wt % β-casein) the initial rheology of the adsorbed surface layer is dominated by a viscous response of the interface. For solutions in the range 5 × 10-3 to 2 × 10-2 wt %, interfacial gelation is observed after ∼15 h of aging, long after the surface tension has stabilized. In particular, although both components of the complex interfacial shear modulus (i.e., the storage and loss moduli) gradually increase with aging time, the ratio of the loss to the storage modulusthe loss tangentdecreases and drops below unity. The frequency dependence of the shear modulus is consistent with sol−gel transitions observed in bulk systems and described within the context of percolation theory.

A molecular brush copolymer, composed of electrooptically active poly(3-substituted thiophene) and thermally responsive poly(Nisopropylacrylamide), displays an exceedingly high water-solubility and unique thermochromic behavior. For more information, see the Communication by R. L. McCarley et al. on the following pages.

Butanethiol was used in ultraviolet-initiated thiol-ene reaction with canola and corn oils to produce sulfide-modified vegetable oils (SMVO). The crude SMVO product was successfully purified by solvent extraction, vacuum evaporation, and silica gel chromatography. The SMVO products were characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Further product characterization and analysis was conducted using GC and GC-MS on the fatty acid methyl esters obtained by the transesterification of the SMVO products. Investigation of the effect of reaction conditions showed that high yield and high conversion of double bonds into thiol were favored at low reaction temperatures and high butanethiol/vegetable oil ratios. Canola and corn oils gave similar double-bond conversions and yields of the desired SMVO product even though they have big differences in the relative numbers of single and multiple double bonds in their structures. Under best reaction conditions, up to 97% of double-bond conversion and 61% isolated yields of the purified SMVO products were attained.

In this work we study experimentally the lifetime of oil droplets pressed by buoyancy against a large oil/water interface, in a system containing protein (bovine serum albumin). The stability of the drops depends strongly on their size, which can be explained with the hydrodynamics of thinning of the gap region. Two distinct size intervals with different thinning regimes may be discerned: (i) Very small drops (below ∼20 µm). They remain practically nondeformed up to coalescence; in this case the lifetime diminishes with increase of the drop radius. The latter trend may be described qualitatively in terms of the Taylor law (or mixed Stokes-Taylor law) for viscous resistance. (ii) Large drops. They form films, and the lifetime rises with the increase of the size, which complies with the Reynolds law for the friction in the gap. The overall dependence of the lifetime on the drop radius passes through a shallow and broad minimumshere for the first time this is proved by direct measurement in a real system: only the drop size is varied with all other experimental conditions being the same.

A none-washing technique for layer-by-layer deposition of polyelectrolyte on colloids based on careful monitoring of colloid recharging is elaborated. It allows applying the technique for colloid systems in larger scale than laboratory, and avoiding the expensive washing procedure with centrifugation or filtration. The colloidal aggregation process depends on the cycle of sequential polycation/polyanion deposition and molecular weight of the polyelectrolytes used. The aggregation can be reversed by the addition of the next polyelectrolyte layer.

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Vegetable oils containing thioether groups have been synthesized and used to effectively remove heavy metal ions from aqueous solution. The use of thioether-functionalized corn oil (TF-corn oil) and thioether-functionalized canola oil (TF-canola oil) were both effective in the extraction of Ag+ from a 600 ppm aqueous silver nitrate solution. The TF-corn oil reduced the observed silver in solution to a level below the detection limit, whereas the TF-canola oil was only able to remove slightly over 50% of the concentration. A study of the absorption rate is also reported, where both the TF-corn oil and the TF-canola oil removed the Ag+ rapidly, at nearly the same rate. Preliminary results suggest that the efficacy and capacity of silver removal relates directly to the fatty acid composition of the oil precursor.

Lipoyl glycerides were synthesized by enzymatic transesterification of lipoic acid with high-oleic sunflower oil in 2-methyl-2-butanol solvent. The synthesis gave a crude product mixture comprising unreacted lipoic acid, free fatty acids, and several lipoyl glyceride structures of varying lipoic acid substitution. A more purified product mixture, devoid of unreacted lipoic acid and free fatty acids, was obtained in 61% yield. The crude and purified product mixtures were thoroughly characterized and their components positively identified. The tribological properties of the product mixtures were further investigated using a variety of methods. The product mixtures displayed significantly improved oxidation stability, cold-flow, and extreme pressure properties over those of the parent high-oleic sunflower oil. The extreme pressure results for the neat products showed a higher weld point for the crude than for the purified mixture. This was attributed to differences in the chemical properties of the components in the two product mixtures.