Mechanism of ultrasound scission of a silver-carbene coordination polymer.

Scission of a supramolecular polymer-metal complex can be carried out using collapsing cavitation bubbles created by ultrasound. Although the most plausible scission mechanism of the coordinative bonds is through mechanical force, the influence of radicals and high hot-spot temperatures on scission has to be considered. A silver(I)-N-heterocyclic carbene complex was exposed to 20 kHz ultrasound in argon, nitrogen, methane, and isobutane saturated toluene.

Sound-driven fluid dynamics in pressurized carbon dioxide.

Using high-speed visualization we demonstrate that ultrasound irradiation of pressurized carbon dioxide (CO(2)) induces phenomena that do not occur in ordinary liquids at ambient conditions. For a near-critical mixture of CO(2) and argon, sonication leads to extremely fast local phase separation, in which the system enters and leaves the two-phase region with the frequency of the imposed sound field. This phase transition can propagate with the speed of sound, but can also be located at fixed positions in the case of a standing sound wave.

Controlled methyl chloride synthesis at mild conditions using ultrasound irradiation.

A new route for the chlorination of methane is described using ultrasound irradiation, which allows for an intrinsically safe process at ambient pressure and temperature. By tuning the gas feed composition methyl chloride yields of up to 19% have been obtained.

Importance of acoustic shielding in sonochemistry.

It is well known that sonochemistry is less efficient at high acoustic intensities. Many authors have attributed this effect to decoupling losses and shielding of the acoustic wave. In this study we investigate both phenomena for a 20 kHz ultrasound field with an intensity ranging from 40 to 150 W/cm2.

Pressure-induced reduction of shielding for improving sonochemical activity.

The effect of hydrostatic pressure on chemical reactions induced by 20 kHz ultrasound has been studied using three different methods: the oxidation of potassium iodide, bubble cloud visualization studies, and sound attenuation measurements. The latter two have demonstrated that shielding of the ultrasonic wave is less pronounced at elevated pressures. Accordingly, the yield of iodine liberation increases with increasing pressure.

Inhibition of nonlinear acoustic cavitation dynamics in liquid CO2.

The authors present a model to study ultrasound-induced cavitation dynamics in liquid carbon dioxide (CO(2)), which includes descriptions for momentum, mass, and energy transport. To assist in the interpretation of these results, numerical simulations are presented for an argon cavity in water. For aqueous systems, inertia effects and force accumulation lead to a nonlinear radial motion, resulting in an almost adiabatic compression of the cavity interior.