Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways

The chemical effects of ultrasound derive primarily from acoustic cavitation. Bubble collapse in liquids results in an enormous concentration of energy from the conversion of the kinetic energy of the liquid motion into heating of the contents of the bubble. The high local temperatures and pressures, combined with extraordinarily rapid cooling, provide a unique means for driving chemical reactions under extreme conditions. A diverse set of applications of ultrasound to enhance chemical reactivity has been explored with important uses in synthetic materials chemistry. For example, the sonochemical decomposition of volatile organometallic precursors in low-volatility solvents produces nanostructured materials in various forms with high catalytic activities. Nanostructured metals, alloys, oxides, carbides and sulfides, nanometer colloids, and nanostructured supported catalysts can all be prepared by this general route. Another important application of sonochemistry in materials chemistry has been the preparation of biomaterials, most notably protein microspheres. Such microspheres have a wide range of biomedical applications, including their use in echo contrast agents for sonography, magnetic resonance imaging, contrast enhancement, and oxygen or drug delivery. Other applications include the modification of polymers and polymer surfaces.

Applications of ultrasound to materials chemistry

Chemical kinetic modeling of hydrocarbon combustion

GALLEX solar neutrino observations: Results for GALLEX IV

Inspired by the unique and efficient wound healing processes in biological systems, several approaches to develop synthetic polymers that can repair themselves with complete, or nearly complete, autonomy have recently been developed. This review aims to survey the rapidly expanding field of self-healing polymers by reviewing the major successful autonomic repairing mechanisms developed over the last decade. Additionally, we discuss several issues related to transferring these self-healing technologies from the laboratory to real applications, such as virgin polymer property changes as a result of the added healing functionality, healing in thin films v. bulk polymers, and healing in the presence of structural reinforcements.

Self-healing polymers and composites

Ultrasonic degradation of polymers in solution

Kinetic Studies on the Acid Hydrolysis of Dextran

Very sensitive and accurate elastic light scattering (LS) measurements have been carried out on mixtures of water with methanol, ethanol, 1-propanol and 2-propanol. Methanol showed no particular effect, while ethanol, 2-propanol and 1-propanol showed signs of increasing cluster formation at a composition of 1 alcohol molecule to 5 water molecules. For the mixture of 1-propanol with water, additional measurements of the quasielastic light scattering have been made and the hydrodynamic radii of the clusters have been calculated. This led to the suggestion of a cluster consisting of 8 1-propanol molecules and a solvation envelope of about 40 water molecules. The concentration of this cluster was determined by elastic LS to be 83% of the total solution weight at 25°C and a composition of 40% by weight 1-propanol in water. The clusters appear to be rather stable, as the hydrodynamic radius showed no significant variation with temperature in the 5° to 50°C range. The concentration was however temperature dependent, as could be shown with elastic LS.

Formation of Clusters in 1-Propanol/Water-Mixtures

Die Abbaureaktion von Dextran durch Ultraschall wurde im Molekulargewichtsbereich von 30 000 bis 90 000 in verschiedenen Losungsmitteln untersucht. Die Abbauprodukte wurden durch ihre Molekulargewichtsverteilungen, die mit Hilfe von Chromatographie an porosem Glas bestimmt wurden, charakterisiert. Aus den Ergebnissen der Untersuchungen konnte abgeleitet werden, das die Abbaureaktion nach erster Ordnung verlauft, die Abbaukonstante proportional dem Molekulargewicht ist, und die Molekule bevorzugt in zwei nahezu gleichgrose Bruchstucke zerfallen. Die Art des Losungsmittels hat dabei einen erheblichen Einflus auf die Abbaukonstanten; es wurde gefunden, das diese der molaren Verdampfungsenthalpie des Losungsmittels direkt proportional sind. Der Einflus der Konformation des Polymeren auf die Abbaukonstanten wurde studiert, wobei sich ergab, das mit einer Aufweitung der Polymerknauel die Abbaukonstanten groser wurden.



Die Ergebnisse bestatigen die allgemeine Auffassung, das die Kavitaten, die bei der Ultrabeschallung entstehen, fur die Abbaureaktion verantwortlich sind. Eine eindeutige Entscheidung, ob die inhomogenen Stromungsfelder oder die Stoswellen, die bei der Implosion der Kavitaten entstehen, fur den Molekulbruch letztlich masgebend sind, kann mit den bisher vorliegenden Ergebnissen nicht getroffen werden. Der Befund, das aufgeweitete Knauel leichter abgebaut werden, spricht fur den Stoswellenmechanismus. Andererseits wird ein Modell fur die Abbaureaktion angegeben, in dem beide Effekte insoweit zusammenwirken, das die inhomogenen Stromungsfelder das Polymerknauel zunachst strecken und die nachfolgende Stoswelle den Molekulbruch bewirkt.



The degradation reaction of dextran by the action of ultrasound was investigated within the molecular weight range from 30 000 to 90 000 in different solvents. The degradation products were characterized by their molecular weight distributions obtained by chromatography on porous glass. From the results of the experiments it could be shown that degradation follows a first order reaction, that the rate constant of degradation is proportional to the molecular weight, and that the molecules break preferentially into two parts of approximately equal size. The nature of the solvent has a considerable effect on the rate constants, which could be shown to be proportional to the enthalpy of vaporization of the solvent. The effect of polymer conformation on the degradation constants was studied and it was found that the degradation constants increase with expansion of the polymer coils.



The experimental results confirm the general assumption, that the cavities, which are caused by ultrasound, are responsible for the degradation reaction. It is not possible, however, to conclude from the experimental results known so far, whether the inhomogenous flow fields or the shock waves, which arise from the collapse of cavitation bubbles, are responsible for the rupture of the molecule. The experimental result, that expanded polymer coils are more easily degraded. favours the mechanism which implies shock waves. Furthermore, a model in which both effects are acting together, in the way that the inhomogeneous flow fields at first stretch the polymer coil, whereas the shock wave, which immediately follows, breaks the molecule, is suggested to explain the rupture of the molecules.

Zum Mechanismus des Abbaus von Polymeren in Lösung durch Ultraschall

Grenzflächenspannungen, Tropfengrößen und Kontaktwinkel im Zweiphasensystem H2O/CO2 bei Temperaturen von 298 bis 333 K und Drücken bis 30 MPa

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