A redox-initiated xylan–poly(sodium acrylate) graft copolymer

An aspen 4-O-methylglucuronoxylan was grafted with poly(sodium acrylate) (PSA) in 3.4N NaOH at 25–30°C. with the use of a persulfate–thiosulfate redox initiator system. The formation of a true graft copolymer was indicated by fractional precipitation and light-scattering studies, physical mixtures of the two pure polymers being used as references. A grafted fraction was isolated, containing no ungrafted xylan but possibly some PSA homopolymer, which contained 96.5% PSA and 3.5% xylan, or an average of 3.2 PSA chains of M?_n approximately 90,500 per xylan chain of M?_n approximately 10,500.     

A theoretical study of cavitation generated by an extracorporeal shock wave lithotripter

The intense acoustic wave generated at the focus of an extracorporeal shock wave lithotripter is modeled as the impulse response of a parallel RLC circuit. The shock wave consists of a zero rise time positive spike that falls to 0 at 1 microsecond followed by a negative pressure component 6 microseconds long with amplitudes scaled to +1000 and -160 bars, P+ and P-, respectively. This pressure wave drives the Gilmore-Akulichev formulation for bubble dynamics; the zero-order effect of gas diffusion on bubble response is included. The negative pressure component of a 1000-bar shock wave will cause a preexisting bubble in the 1- to 10-microns range to expand to over 100 times its initial size, R0, for 250 microseconds, with a peak radius of approximately 1400 microns, then collapse very violently, emitting far UV or soft x-ray photons (black body). Gas diffusion does not appreciably mitigate the amplitude of the pressure wave radiated at the primary collapse, but does significantly reduce the collapse temperature. Diffusion also increases the bubble radius from R0 up to 40 microns and extends the duration of ringing following the primary collapse, assuming that the bubble does not break up or shed microbubbles. Results are sensitive to P+/P- and to the duration of the negative pressure cycle but not to rise time.     

An improved understanding of the dispersion of multi-walled carbon nanotubes in non-aqueous solvents

Regenerable antimicrobial N-halamine/silica hybrid nanoparticles (NPs) containing chlorinated 5,5-dimethylhydantoinyl (Cl-DMH) groups, Cl-DMH/SiO₂ hybrid NPs, have been prepared by a co-condensation reaction between N-(3-triethoxysilylpropyl)-5,5-dimethylhydantoin (TS-DMH) and tetraethoxysilane (TEOS) and then a chlorination reaction in NaClO solution. The as-synthesized Cl-DMH/SiO₂ NPs were characterized by transmission electron microscopy, Scanning electron microscopy, X-ray photoelectron spectra, Specific surface area, Differential scanning calorimetry, and Fourier transform infrared. Experimental results showed that the size of the as-synthesized Cl-DMH/SiO₂ NPs could be well adjusted by changing the mass ratio of TS-DMH/TEOS and the volume ratio of 28 % NH₄OH/H₂O. Antimicrobial tests showed that the as-prepared Cl-DMH/SiO₂ hybrid NPs had excellent antimicrobial activities against both Escherichia coli and Staphylococcus aureus. The minimum inhibitory concentration and minimum bactericidal concentration values of the as-prepared Cl-DMH/SiO₂ hybrid NPs are 15 and 20 μg/mL for S. aureus, 25 and 30 μg/mL for E. coli, respectively. Paper disk diffusion assay showed that smaller-sized Cl-DMH/SiO₂ hybrid NPs have bigger inhibition zone diameters, indicating stronger antimicrobial efficacies. Also, the storage stability and regenerability of Cl-DMH/SiO₂ hybrid NPs were investigated.