The uses of ultrasound in food technology

The same physical and mechanical effects which have been utilised in sonochemistry, i.e. strong shear forces, particle fragmentation, increased mass and heat transfer, nucleation of seedling, have been applied to food processing. Examples are quoted from various applications where power ultrasound has been used to influence the development of living cells, improve sterilisation and effect enzyme activity. Typically ultrasound can be used as a processing aid in extraction, crystallisation, freezing, emulsification, filtration and drying.     

Quantification of frequency dependence of mechanical effects induced by ultrasound

The physical or mechanical effects induced by ultrasound were investigated through the viscosity change in degradation of polymers. The viscosity change was observed with polyethylene oxide in both aqueous and benzene solution; while polystyrene in only benzene solution. The frequency of ultrasound in these experiments varies from 20 kHz to 1 MHz, under a constant dissipated power. The viscosity ratio and the apparent degradation rate were obtained as a function of the irradiation frequency. From the analysis of these experiments, the mechanical effects are found to slow down above 100 kHz when the frequency increases. In case of the analysis of solution viscosity, since this method yields the same apparent results in both aqueous and benzene solutions, our study propose an alternative simple, cost effective method to quantify the mechanical effects in sonochemistry.     

Energy analysis during acoustic bubble oscillations: Relationship between bubble energy and sonochemical parameters

In this work, energy analysis of an oscillating isolated spherical bubble in water irradiated by an ultrasonic wave has been theoretically studied for various conditions of acoustic amplitude, ultrasound frequency, static pressure and liquid temperature in order to explain the effects of these key parameters on both sonochemistry and sonoluminescence. The Keller–Miksis equation for the temporal variation of the bubble radius in compressible and viscous medium has been employed as a dynamics model. The numerical calculations showed that the rate of energy accumulation, dE/dt, increased linearly with increasing acoustic amplitude in the range of 1.5–3.0 atm and decreased sharply with increasing frequency in the range 200–1000 kHz. There exists an optimal static pressure at which the power w is highest. This optimum shifts toward a higher value as the acoustic amplitude increases. The energy of the bubble slightly increases with the increase in liquid temperature from 10 to 60 °C. The results of this study should be a helpful means to explain a variety of experimental observations conducted in the field of sonochemistry and sonoluminescence concerning the effects of operational parameters.     

Using sonochemistry for the fabrication of nanomaterials

One of the reasons for the huge interest in nanomaterials originated because of the prohibitive price that commercial companies have to pay for introducing new materials into the market. Nanotechnology enables these companies to obtain new properties using old and recognized materials by just reducing their particle size. For these known materials no government approval has to be obtained. Thus, the interest in nanomaterials has led to the development of many synthetic methods for their fabrication. Sonochemistry is one of the earliest techniques used to prepare nanosized compounds. Suslick, in his original work, sonicated Fe(CO)5 either as a neat liquid or in a decalin solution and obtained 10-20 nm size amorphous iron nanoparticles. A literature search that was conducted by crossing Sono* and Nanop* has found that this area is expanding almost exponentially. It started with two papers published in 1994, two in 1995, and increased to 59 papers in 2002. A few authors have already reviewed the fields of Sono and Nano. It should be mentioned that in 1996, Suslick et al. published an early review on the nanostructured materials generated by ultrasound radiation. Suslick and Price have also reviewed the application of ultrasound to materials science. This review dealt with nanomaterials, but was not directed specifically to this topic. The review concentrated only on the sonochemistry of transition metal carbonyls and catalytic reactions that involve the nanoparticles resulting from their sonochemical decomposition. Grieser and Ashokkumar have also written a review on a similar topic. A former coworker, Zhu, has recently submitted for publication a review article entitled "Novel Methods for Chemical Preparation of Metal Chalcogenide Nanoparticles" in which he reviews three synthetic methods (sonochemistry, sonoelectrochemistry, and microwave heating) and their application in the synthesis of nanosized metal chalcogenides. Although still unpublished, I myself have recently written a review discussing novel methods (sonochemistry, microwave heating, and sonoelectrochemistry) for making nanosized materials. The current review will: (1) Present the four main advantages that sonochemistry has over other methods related to materials science and nanochemistry; (2) concentrate on the more recent (2003) literature that was not reviewed in the previously-mentioned reviews, and (3) focus on a specific question, such as what is the typical shape of products obtained in sonochemistry? This review will not survey the literature related to sonoelectrochemistry.     

Ultrasound and polar homogeneous reactions

The effect of ultrasound on the rates of homogeneous heterolytic reactions not switched to a free radical pathway can be explained by the perturbation of the molecular organization of or the solvation in the reacting system. A quantitative analysis of the sonochemical acceleration on the basis of the microreactor concept was carried out. It was found that (1) the Diels-Alder reaction cannot be accelerated by ultrasound except when SET or free radical processes are promoted, (2) the rectified diffusion during cavitation cannot be responsible for the acceleration of reactions, and (3) the sonochemical acceleration of polar homogeneous reactions takes place in the bulk reaction medium. This implies the presence of a 'sound-field' sonochemistry besides the 'hot-spot' sonochemistry. The occurrence of a sonochemical deceleration effect can be predicted.     

超声波在食品技术中的应用

强超声在媒质中传播时产生力学效应、空化效应和热效应,产匝此增强质量传输和热传递,对介质产生强的切向力。本文对超声波在辅助或强化提取,冷冻、乳化、结晶和干燥等食品的加工技术中应用加以综述。     

Power ultrasound in metal-assisted synthesis: From classical Barbier-like reactions to click chemistry

The search for more efficient and greener synthetic procedures to obtain highly functionalized chemical structures has always found in metal-assisted reactions a noteworthy strategy. All these reactions fall in the main domain of sonochemistry; in fact few techniques can compete with power ultrasound in so efficiently activating a metal surface, thus enhancing and accelerating its subsequent reaction with an organic substrate. Young researchers will certainly benefit from the rich literature and past experience of several pioneers who have, since the early eighties, laid the foundations of modern sonochemical synthetic protocols. Herein we provide a concise overview that describes how ultrasound acts in such a way as to make it a fundamental tool in improving the classical one-step coupling promoted by zero-valent metal species, usually referred to as Barbier-like reactions. From early hallmarks to recent accomplishments, especially the latest Cu-catalyzed alkyne-azide reaction (the so-called Click reaction), intended to be a universal ligation in chemistry and biology; we highlight the role and crucial effects of sonication on these processes.     

Potential uses of ultrasound in the biological decontamination of water

In the past there was a prevailing feeling in industry that power ultrasound would be too expensive to use for water treatment on an industrial scale. This was based on calculations involving the direct scale up of power consumption in small-scale (generally batch) laboratory experiments. In recent times this attitude has changed somewhat as a result of the installation of a number of ultrasonic devices in operational water or sewage treatment plants. In our laboratories we have investigated the decontamination of water under the influence of ultrasound alone and in conjunction with other treatments. The results, particularly when applied to flowing systems, indicate a real future for sonochemistry in water treatment.     

Enhancing sonochemical activity in aqueous media using power-modulated pulsed ultrasound: an initial study

Relatively little is known about the effects of pulsed ultrasound on the facilitation of chemical reactivity. Previous studies have indicated that sonochemistry using pulses is generally less effective than continuous ultrasonic irradiation. However, the pulse trains employed were such that the peak power of the pulses was the same as the maximum power used in continuous irradiation. As a result, less acoustic energy was transmitted to the solutions over the same period of time. The effectiveness of ultrasound when the pulse is adjusted so that the same amount of acoustic energy is input compared to continuous irradiation over a given time has not been previously explored. In this study we have embarked on an examination of the efficacy of power-modulated pulsed (PMP) sonochemistry. Specifically, we have explored the effects of pulse type and pulse frequency on the oxidation of potassium iodide and the degradation of acid orange, a common industrial colorant. A rate increase by a factor of three was observed compared with continuous irradiation under conditions of equivalent acoustic input power.     

A review on textile sonoprocessing: A special focus on sonosynthesis of nanomaterials on textile substrates

The chemical and physical effects of ultrasound with a frequency above 16 kHz, higher than the audible frequency of the human ear, have proven to be a useful tool for variety of systems ranging from the application of ultrasound in environmental remediation to the cooperation of ultrasound waves with chemical processing regarding as sonochemistry. Ultrasound opened up new advances in textile wet processing including desizing, scouring, bleaching, dyeing, printing and finishing and also nanoprocessing including nanopretreatment, nanodyeing, nanoprinting and nanofinishing. Use of ultrasound appears to be a promising alternative technique to reduce energy, chemicals and time involved in various operations. Over the past years there has been an enormous effort on using sonochemistry for the synthesis of nanomaterials on various textile materials. In situ sonosynthesis of nanoparticles and nanocomposites on different textiles is a pioneering approach driving future investigations. With such wide range of applications and vast ever increasing publications, the objective of this paper is presenting a comprehensive review on ultrasound application in textile from early time to now by the main emphasis on the sonosynthesis of nanomaterials outlining directions toward future research.     

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. Visualization of the bubble cloud has demonstrated that the void fraction below the ultrasound horn increases more than proportional with increasing power input. Nevertheless, the energy coupling between the horn and the liquid remains constant; this implies that decoupling losses are not reinforced for larger bubble clouds. On the contrary, microphone measurements have shown that due to the larger bubble cloud a substantial part of the supplied energy is lost at high power inputs. In striving towards more efficient sonochemistry, reduction of shielding appears as one of the major challenges.     

Doping nanoparticles into polymers and ceramics using ultrasound radiation

In materials science, sonochemistry is mostly used for the fabrication of nanomaterials, but it has also been used for the polymerization of monomers. The current review is aimed at introducing a new application of sonochemistry to materials science, i.e., the doping of nanoparticles into polymers and ceramic bodies. The introduction will present a short overview of sonochemistry, and will outline the advantages of sonochemistry as a tool for fabricating nanomaterials.     

Sonochemical and photochemical oxidation of organic matter

Recent developments in sonochemistry have led us to study its use to treat water and wastewater. The effects of ultrasound wave in hydrophilic chemical oxidations are mainly due to hydroxyl radical production during the cavitation-induced water decomposition. Currently, the sonochemical destruction of aromatic compounds in water solution is obtained with low rates. The aim of this work is to evaluate the efficiency of the sonochemical effect in conjunction with a photochemical irradiation. Taking phenol as an example, the combined action of sonochemistry and photochemistry has been considered in a ‘sonuv’ reactor. An important enhancement of the degradation rate of phenol has been observed. It may be the result of three different oxidative processes: direct photochemical action, high frequency sonochemistry and reaction with ozone (produced by UV irradiation of air). The process has been successfully tested to lower the chemical oxygen demand of a municipal wastewater.     

Invariance of the Doppler bandwidth with flow displacement in the illuminating field.

It is known that if single frequency continuously transmitted ultrasound or electromagnetic energy is reflected from "straight line flow," defined here as one or more scatters moving with constant velocity along an infinite straight line, the Doppler effect will shift the echo spectrum center frequency from the transmitted value, and broaden its bandwidth. It is proved that if such straight line flow is shifted laterally or in range anywhere in the field, i.e., without change of orientation, its Doppler bandwidth remains unchanged. (The "Doppler bandwidth" is here defined as the frequency difference between the extrema of the echo power spectrum.) The theorem holds true even though the time domain echo changes dramatically with motion of the flow path, and is believed to be valid for electromagnetic as well as ultrasound waves. Its implications with respect to flow measurement, as well as preliminary experimental and computational confirmation, will be discussed.     

Calorimetric study of the energy efficiency for ultrasound-induced radical formation

Energy conversion in sonochemistry is known to be an important factor for the development of industrial applications, however, the strong influence of the physical properties of the liquid on the ultrasound characteristics usually prevents an accurate determination of the chemical effects. In this study, the energy efficiency of the ultrasound-induced radical formation from methyl methacrylate has been investigated. The energy yield can be quantified by comparison of the ultrasonic power that is transferred to the liquid and the radical formation kinetics. Based on this method the influence of temperature and amplitude of the ultrasound horn on the energy efficiency has been determined. The energy yield for the formation of radicals from ultrasonic waves appears to be in the order of 5 x 10(-6) J/J. The energy conversion is the highest at low temperatures and at low amplitudes.     

Sonochemical fabrication of inorganic nanoparticles for applications in catalysis

Catalysis covers almost all the chemical reactions or processes aiming for many applications. Sonochemistry has emerged in designing and developing the synthesis of nano-structured materials, and the latest progress mainly focuses on the synthetic strategies, product properties as well as catalytic applications. This current review simply presents the sonochemical effects under ultrasound irradiation, roughly describes the ultrasound-synthesized inorganic nano-materials, and highlights the sonochemistry applications in the inorganics-based catalysis processes including reduction, oxidation, degradation, polymerization, etc. Or all in all, the review hopes to provide an integrated understanding of sonochemistry, emphasize the great significance of ultrasound-assisted synthesis in structured materials as a unique strategy, and broaden the updated applications of ultrasound irradiation in the catalysis fields.     

Self-repeating properties of four-petal Gaussian vortex beams in quadratic index medium

In this paper, we investigate the propagation properties of four-petal Gaussian vortex (FPGV) beams propagating through the quadratic index medium, obtaining the analytical expression of FPGV beams. The effects of beam order n, topological charge m and beam waist ${\omega }_0$ are investigated. Results show that quadratic index medium support periodic distributions of FPGV beams. A hollow optical wall or an optical central principal maximum surrounded by symmetrical sidelobes will occur at the center of a period. At length, they will evolve into four petals structure, exactly same as the intensity distributions at source plane.     

Upper limits on the mechanical loss of silicate bonds in a silicon tuning fork oscillator

Silicon optics suspended by silicon ribbons or silicon fibers and kept at low temperature are being considered, because of promising optical and mechanical properties, for the test masses of third generation interferometric gravitational-wave detectors. To interconnect the suspension elements the technique of hydroxide catalysis (or silicate) bonding can be used. In order to estimate the bond loss a tuning fork was fabricated from silicon ribbons, which were then silicate bonded. The temperature dependence of mechanical loss of this tuning fork was measured in the temperature range of 95–295 K. The ratio of the energy stored in the bond layer to the total energy of the tuning fork was calculated by numerical simulation. This provided an upper limit of the bond loss as a function of the temperature. It is $(5\pm 2)\times {10}^{?3}$ at 123 K, a proposed operating temperature of cryogenically operating ground based interferometric gravitational-wave detectors.