PubMed Health⌕ Search

Biomedical subjects

Franz Grieser

Publications and source records attributed to Franz Grieser.

27 records · Page 2Linked to original sources
PubMed2004

Single bubble sonoluminescence--a chemist's overview.

The phenomenon of sonoluminescence has been known for over 60 years but it is only over the last few years that a better understanding of its origins has emerged. In part the discovery of single bubble sonoluminescence, just over 10 years ago, has been a major contributor to the theoretical advances that have been made to account for the event. This Minireview is from the perspective of a physical chemist and considers the progress that has been made in understanding the role of solutes in affecting the sonoluminescence from a solution exposed to ultrasound. The physicochemical properties of solutes that are important in controlling both single bubble and multibubble sonoluminescence are discussed.

Journal Article↗
PubMed2004

Sonoluminescence quenching of organic compounds in aqueous solution: frequency effects and implications for sonochemistry.

Solute-induced quenching of sonoluminescence (SL) is reported for aqueous solutions of two homologous series of methyl esters and ketones using low (20 kHz) and high (515 kHz) ultrasound frequencies. SL data at 20 kHz from aqueous solutions containing alcohols and carboxylic acids are also presented to compare with previously published results at 515 kHz. In addition to supporting the previous findings on the existence of stable and transient bubbles at 515 and 20 kHz, respectively, the results suggest that the hydrogen-bonding characteristics of the solutes also play a major role in the extent of SL quenching. An increase in the SL intensity at low concentrations for most of the solutes suggests that these solutes increase the number of "active" bubbles by hindering the coalescence of bubbles. It is concluded that the effect of the solutes on the SL signal from aqueous solutions at both frequencies is primarily due to the balance of two factors, namely, the incorporation of solute within the bubble, leading to SL quenching, and the prevention of coalescence of the bubbles, leading to SL enhancement. At the higher frequency, SL quenching by the solutes is the main influence on the emission yield. However, at the lower frequency, hindrance to coalescence by the solutes dominates at lower concentrations and leads to SL enhancement. The implications of these results for optimizing conditions for aqueous sonochemical reactions are discussed.

Journal Article↗
PubMed2003

PAA/PEO comb polymer effects on rheological properties and inter-particle forces in aqueous silica suspensions.

The effects of a poly(acrylic acid) (PAA)-poly(ethylene) (PEO) comb polymer dispersant on the rheological properties and inter-particle forces in aqueous silica suspensions have been studied under varying pH conditions. The comb polymer was found to adsorb more strongly under acidic than basic conditions, indicating that the PAA backbone of the copolymer preferentially adsorbs onto silica surfaces with the PEO "teeth" extending out from the surface into the solution. In the presence of low concentrations of copolymer, the silica suspensions were stable due to electrostatic repulsions between the silica surfaces. At higher copolymer concentrations and under neutral and basic conditions, where the copolymer interacted only weakly with silica, the suspensions showed a transition from a dispersed to weakly flocculated state and attractive forces were measured between silica surfaces. Under acidic conditions, the silica dispersion also destabilized at intermediate copolymer adsorbed density and then was re-stabilized at higher adsorbed coverage. The silica suspensions were stable at high copolymer coverage due to steric repulsions between the particles. The destabilization at intermediate coverage is thought to be due to polymer bridging between particles or possibly depletion forces.

Journal Article↗
PubMed2003

Sonochemical production of fluorescent and phosphorescent latex particles.

A novel method for producing nanosized polymer latex particles doped with fluorescent and phosphorescent solutes is described. Methyl methacrylate monomer (10 wt %) containing either pyrene, 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DMDP), or 1-bromonaphthalene was ultrasonically dispersed in water and simultaneously polymerized to produce approximately 60 nm diameter latex particles. A fluorescence spectroscopic examination of the latex dispersion containing either pyrene or DMDP showed that the solutes were not covalently bound to the polymer and that they were embedded in a highly viscous environment possessing a low polarity (dielectric constant on the order of 2). The fluorescence lifetime of the pyrene in the core of the poly(MMA) latex was found to be 520 ns, irrespective of the oxygen concentration in the dispersion. Room-temperature phosphorescence was observed from 1-bromonaphthalene, with a lifetime of 2.0 ms in an argon atmosphere. In the presence of air, phosphorescence was still observable although with a partially reduced emission intensity.

Journal Article↗
PubMed2003

The effects of microgravity on nanoparticle size distributions generated by the ultrasonic reduction of an aqueous gold-chloride solution.

A solution of gold chloride was reduced using ultrasound irradiation to prepare metallic gold nanoparticles under conditions of microgravity and normal gravity at sea level. Particle size distributions were measured using TEM analysis. A mean particle diameter of 10 nm was obtained in microgravity while a mean diameter of 80 nm was obtained in the laboratory. Absorbance measurements on the reacted solution found an enhanced reduction rate in the reduction of gold chloride in microgravity compared to that in the laboratory.

Journal Article↗
PubMed2002

Emulsion polymerization synthesis of cationic polymer latex in an ultrasonic field.

Poly(methyl methacrylate) and poly(butyl acrylate) lattices have been synthesized under ultrasonic irradiation in the presence of a cationic surfactant, dodecyltrimethylammonium chloride. The polymerization of oil-in-water emulsions of monomeric species was carried out at 30 degrees C (+/-5 degrees C) in the absence of a chemical initiator. The lattices were formed as stable dispersions with particle diameters spanning the range of 40-150 nm and with polymer molecular weights greater than 10(6) g mol(-1). The results obtained strongly support a polymerization process involving a miniemulsion system, in which continuous nucleation of particles takes place throughout the monomer to polymer conversion reaction.

Journal Article↗
PubMed2002

Effect of surfactants, polymers, and alcohol on single bubble dynamics and sonoluminescence.

The radial dynamics of an acoustically driven single bubble, levitated in water, along with the sonoluminescence (SL) signal, were recorded in the absence and in the presence of micromolar quantities of different surfactants and polymers. It was observed that these nonvolatile solutes, in the low concentration range used, did not significantly affect the radial dynamics nor the SL intensity of a single bubble in water. In contrast, the addition of micromolar quantities of a volatile solute, pentanol, quenched approximately 90% of the SL without affecting the radial dynamics of the bubble.

Journal Article↗
PubMed2001

The Adsorption of Dodecyltrimethylammonium Bromide on Mica in Aqueous Solution Studied by X-Ray Diffraction and Atomic Force Microscopy.

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution. Copyright 2001 Academic Press.

Journal Article↗