Influence of Particle Morphology and Flow Conditions on the Dispersion Behavior of Fumed Silica in Silicone Polymers

The dispersion behavior of agglomerates of several grades of fumed silica in poly(dimethyl siloxane) liquids has been studied as a function of particle morphology and applied flow conditions. The effects of primary particle size and aggregate density and structure on cohesivity were probed through tensile and shear strength tests on particle compacts. These cohesivity tests indicated that the shear strength of particle compacts was two orders of magnitude higher than the tensile strength at the same overall packing density. Experiments carried out in both steady and time‐varying simple‐shear flows indicate that dispersion occurs through tensile failure. In the steady‐shear experiments,enhanced dispersion was obtained at higher levels of applied stress and, at comparable levels of applied stress, dispersion was found to proceed faster at higher shear rates. Experiments conducted in time‐varying flows further corroborated the results obtained in tensile cohesivity tests. Experiments in which the mean and maximum stresses in the time‐varying flows were matched to the stresses produced in steady shear flows highlight the influence of flow dynamics on dispersion behavior.     

Multiphoton ionization vibrational state selection of H2O, D2O and HDO

We present a study of single color (2 + 1) resonance-enhanced multiphoton ionization (REMPI) of H₂O, D₂O, and HDO via several Rydberg states lying in the energy range from 80 000 to 86 000 cm⁻¹. Photoelectron spectra (PES) show that the corresponding cations can be vibrationally state-selected for most vibrational states. The exception is the bend of H₂O⁺ and HDO⁺, where mixing in the REMPI intermediate level results in weak ion intensity and only 50% state purity.     

Reactions of ortho oxy-substituted benzyl and phenacyl bromides in dimethyl sulphoxide

o-Acetoxy- and o-benzoyloxy-benzyl bromides and tosylates oxidatively rearrange in moist dimethyl sulphoxide to o-hydroxybenzyl esters; o-acetoxy- and o-benzoyloxy- phenacyl bromides rearrange to mixtures of 2-hydroxycoumaran-3-ones and o-hydroxyphenacyl esters; o-hydroxyphenacyl bromides also yield 2-hydroxycoumaran-3-ones, together with o-hydroxyphenacyl alcohols. 2-Acetoxybenzaldehyde is reductively rearranged by sodium borohydride to o-hydroxybenzyl acetate.     

Development of a multiplexed microbioreactor system for high-throughput bioprocessing

A multiplexed microbioreactor system for parallel operation of multiple microbial fermentation is described. The system includes miniature motors for magnetic stirring of the microbioreactors and optics to monitor the fermentation parameters optical density (OD), dissolved oxygen (DO), and pH, in-situ and in real time. The microbioreactors are fabricated out of poly(methylmethacrylate)(PMMA) and poly(dimethylsiloxane)(PDMS), and have a working volume of 150 microl. Oxygenation of the cells occurs through a thin PDMS membrane at the top of the reactor chamber. Stirring is achieved with a magnetic spin bar in the reactor chamber. Parallel microbial fermentations with Escherichia coli are carried out in four stirred microbioreactors and demonstrate the reproducible performance of the multiplexed system. The profiles for OD, DO, and pH compare favourably to fermentations performed in bioreactor systems with multiple bench-scale reactors. Finally, the multiplexed system is used to compare two different reactor designs, demonstrating that the reproducibility of the system permits the quantification of microbioreactor performance.