Rheological studies of the gelation kinetics of Cr+3-polyacrylamide solutions

A new rheological approach for the study of the gelation kinetics of aqueous Cr⁺³ polyacrylamide solutions has been investigated which relies on the assumption that at the gel point, GP, a constant amount of Cr⁺³ will have reacted, independent of the initial Cr⁺³ concentration. From this, a kinetic expression relating GP to the initial concentrations of Cr⁺³ and reactive groups on the polymer has been derived for the case of a crosslinking reaction first order in Cr⁺³ and polymer. Experimental evidence that the amount of Cr⁺³ reacted at the GP is constant for a given polymer and solution pH has been obtained. The good fit of the kinetic expression to the rheological data provides new evidence that the gelation reaction is first order in Cr⁺³ rather than second order as claimed previously.     

Post-buckling dynamic behavior of periodically supported imperfect shells

A circular cylindrical shell, periodically supported and subjected to step-loading in the form of lateral or hydrostatic pressure, is studied. Using the time-dependent von Kármán-Donnell equations, its imperfection sensitivity is examined and a simple asymptotic expression for the dynamic buckling load, valid for small imperfections, is obtained. There is a simple relation, independent of the imperfection, between the dynamic and static buckling loads.     

Diaryliodonium salts as thermal initiators of cationic polymerization

Diaryliodonium salts (I) undergo efficient thermal decomposition in the presence of copper (II) compounds. Such systems can be employed as a novel class of latent thermal initiators for cationic polymerization. An investigation of the mechanism of the reaction demonstrated that the copper (II) compound is first reduced to the corresponding copper (I) compound, which subsequently reduces the diaryliodonium salt. The cationic polymerization of some typical monomers using these new initiators was carried out to demonstrate the scope of their utility.     

2,6-Dimethylphenylnitrene in low-temperature matrices

Photolysis of 2,6-dimethylphenyl azide in N₂ matrices at 12K gives 2,6-dimethylphenylnitrene; in the presence of CO, the nitrene forms the corresponding isocyanate, while on shorter wavelength irradiation, it undergoes an inefficient rearrangement to an azacycloheptatetraene.     

Simultaneous determination of perhexiline and its monohydroxy metabolites in biological fluids by gas chromatography-electron-capture detection

A rapid and sensitive method for the simultaneous determination of perhexiline and its cis-4-axial and trans-4-equatorial monohydroxy metabolites (M1 and M3, respectively) in human plasma, urine and bile is described. The assay utilises a single diethyl ether extraction, heptafluorobutyric acid anhydride derivatisation and separation and detection by gas chromatography-electron-capture detection. The limits of detection are 0.1 microgram/ml for perhexiline and 0.025 microgram/ml for the M1 and M3 metabolites. This method has been used in a five-day kinetic study of three healthy adult males who ingested a single 300-mg dose of perhexiline maleate. One of these volunteer subjects exhibited elevated plasma perhexiline and markedly reduced plasma and urinary M1 concentrations together with profoundly prolonged plasma and urinary M1 elimination times when compared with the other two subjects. These differences are thought to be of genetic origin. There were also obvious differences in urinary M3 concentrations which were discussed.     

Equilibrium and nonequilibrium states in microfluidic double emulsions

We describe experimental and theoretical studies dedicated to establishing the physics of formation of double droplets in microfluidic systems. We show that the morphologies (complete engulfing, partial engulfing, and nonengulfing) obtained at late times minimize the interfacial energy of the system. We explain that nonequilibrium morphologies generated in the system can have long lifetimes. Remarkably, the physics of formation of the double droplets with microfluidics allows the synthesis of particles with new morphologies.