Inertial cavitation initiated by polytetrafluoroethylene nanoparticles under pulsed ultrasound stimulation

Nanoscale gas bubbles residing on a macroscale hydrophobic surface have a surprising long lifetime (on the order of days) and can serve as cavitation nuclei for initiating inertial cavitation (IC). Whether interfacial nanobubbles (NBs) reside on the infinite surface of a hydrophobic nanoparticle (NP) and could serve as cavitation nuclei is unknown, but this would be very meaningful for the development of sonosensitive NPs. To address this problem, we investigated the IC activity of polytetrafluoroethylene (PTFE) NPs, which are regarded as benchmark superhydrophobic NPs due to their low surface energy caused by the presence of fluorocarbon. Both a passive cavitation detection system and terephthalic dosimetry was applied to quantify the intensity of IC. The IC intensities of the suspension with PTFE NPs were 10.30 and 48.41 times stronger than those of deionized water for peak negative pressures of 2 and 5 MPa, respectively. However, the IC activities were nearly completely inhibited when the suspension was degassed or ethanol was used to suspend PTFE NPs, and they were recovered when suspended in saturated water, which may indicates the presence of interfacial NBs on PTFE NPs surfaces. Importantly, these PTFE NPs could sustainably initiate IC for excitation by a sequence of at least 6000 pulses, whereas lipid microbubbles were completely depleted after the application of no more than 50 pulses under the same conditions. The terephthalic dosimetry has shown that much higher hydroxyl yields were achieved when PTFE NPs were present as cavitation nuclei when using ultrasound parameters that otherwise did not produce significant amounts of free radicals. These results show that superhydrophobic NPs may be an outstanding candidate for use in IC-related applications.     

Sonodynamic therapy--a review of the synergistic effects of drugs and ultrasound

Sonodynamic therapy, the ultrasound dependent enhancement of cytotoxic activities of certain compounds (sonosensitizers) in studies with cells in vitro and in tumor bearing animals, is reviewed. The attractive features of this modality for cancer treatment emerges from the ability to focus the ultrasound energy on malignancy sites buried deep in tissues and to locally activate a preloaded sonosensitizer. Possible mechanisms of sonodynamic therapy include generation of sonosensitizer derived radicals which initiate chain peroxidation of membrane lipids via peroxyl and/or alkoxyl radicals, the physical destabilization of the cell membrane by the sonosensitizer thereby rendering the cell more susceptible to shear forces or ultrasound enhanced drug transport across the cell membrane (sonoporation). Evidence against the role of singlet oxygen in sonodynamic therapy is discussed. The mechanism of sonodynamic therapy is probably not governed by a universal mechanism, but may be influenced by multiple factors including the nature of the biological model, the sonosensitizer and the ultrasound parameters. The current review emphasizes the effect of ultrasound induced free radicals in sonodynamic therapy.     

混响场中脉冲超声空化效应的研究

本文实验研究了不同脉冲宽度的８２０ｋＨｚ超声波的空化效应，结果得出，空化致自基产量随脉冲宽度及声强呈现规律性变化，尤其观察到了“脉冲空化峰”现象，本文从液面受迫振动角度出混响场中“脉冲空化峰”现象的机制。     

X-ray absorption spectroscopy studies in supercritical aqueous solutions

ABSTRACT

The past two decades have witnessed significant advances in the application of X-ray absorption spectroscopy (XAS) to the study of supercritical aqueous fluids. The data obtained using in situ XAS have provided insights into the stability and the structure of metal complexes that are fundamental to understanding natural and industrial hydrothermal processes. Important recent advances using XAS can be attributed to the use of new high temperature and pressure autoclaves designed specifically for the analysis of fluids at extreme temperatures and pressures, improved techniques for the acquisition of X-ray absorption spectra and molecular-level computational modelling used in association with XAS analysis. High-brilliance light sources have not only provided new opportunities for XAS investigations of supercritical fluids, but have also revealed the effects of beam-induced radiolysis of the same fluids. The advent of energy-dispersive and rapid-acquisition XAS holds promise for future studies of beam-induced radiolysis and of the kinetics associated with the formation of metal complexes in high-temperature fluids.     

Kinetic sonication effects in aqueous acetonitrile solutions. Reaction rate levelling by ultrasound

The kinetics of the pH-independent hydrolysis of 4-methoxyphenyl dichloroacetate were investigated with and without ultrasonic irradiation in acetonitrile–water binary mixtures containing 0.008 to 35 wt.% of acetonitrile and the kinetic sonication effects (k_son/k_non) were calculated. Molecular dynamics (MD) simulations of the structure of the solutions were performed with ethyl acetate as the model ester. The ester is preferentially solvated by acetonitrile. The excess of acetonitrile over water in the solvation shell grows fast with an increase in the co-solvent content in the bulk solution. In parallel, the formation of a second solvation shell rich in acetonitrile takes place. Significant kinetic sonication effects for the hydrolysis were explained with facile destruction of the diffuse second solvation shell followed by a rearrangement of the remaining solvent layer under sonication. The rate levelling effect of ultrasound was discussed. In an aqueous-organic binary solvent, independent of the solvent composition, the ultrasonic irradiation evokes changes in the reaction medium which result in an almost identical solvation state of the reagent thus leading to the reaction rate levelling.     

Application of ultrasound to textiles washing in aqueous solutions

The ultrasound was applied to textile washing as a mechanical action for soil removal. The polyester fabric was soiled with carbon black or oleic acid as a model contaminant, and washed with the original fabric in aqueous solutions without and with alkali or surfactant by applying ultrasound, shaking or stirring action. The detergency and soil redeposition were evaluated from the change in the surface reflectance of artificially soiled fabrics and the original fabric due to washing. In comparison with shaking and stirring actions, ultrasound was found to remove the particulate and oily soils efficiently in a short time and at low bath ratio. With increasing ultrasound power, the detergency of both soils increased and exceeded that obtained with Wascator, a horizontal axis drum type washer. Using three standard fabrics for determining mechanical action during washing, it was shown that ultrasound washing caused little mechanical damage to the fabric. However, the soil redeposition was frequently observed for ultrasonic washing, especially at low bath ratio.     

水溶液中结合水的定义与量化

水溶液中溶质的结合水具有不同于远离溶质的自由水的结构和性质.结合水的存在对水和溶质结构和动力学性质均具有显著甚至决定性的影响.然而,对结合水动力学和热力学性质的定量理解在诸多方面一直存在争议甚至严重分歧,其中重点包括如何定义和量化结合水,如何表征结合水和自由水的动力学差别,结合水如何参与生物大分子各种生物功能过程,以及溶质或界面影响结合水结构与性质的途径等.给出结合水定义的物理学依据和量化方法,是深入理解上述问题的第一步.本文简述了各种不同谱学方法定义结合水的基本原理及量化的困难,强调具有不同时间和空间响应尺度的测试方法所得结合水数不必完全可比.此外,系列水溶液物性随浓度升高会明显改变其浓度依赖关系,相应拐点浓度常被用于量化稀溶液中的溶质结合水数.我们近期研究的水溶液玻璃化转变温度-浓度关系,为结合水的定义、量化和水溶液的三区划分提供了物理依据,同时揭示了上述利用性质-浓度关系拐点浓度量化结合水方法的不足.     

Two components of Na emission in sonoluminescence spectrum from surfactant aqueous solutions

Sonoluminescence from sodium dodecyl sulfate (SDS) aqueous solutions exhibits Na emission. The spectrum of Na emission was measured as a function of sonication time for a total of 30 min at an ultrasonic frequency of 148 kHz. The spectral line profiles changed with the sonication time, suggesting that the Na emission consists of two components: broadened lines, which are shifted from the original D lines, and unshifted narrow lines. The intensity of the unshifted narrow lines decreased at a greater rate than that of the broadened lines with increasing sonication time. This effect was enhanced at a higher acoustic power. The shifted broadened lines remained after sonication for 30 min. We propose that these quenching effects are caused by the accumulation of gases decomposed from SDS molecules inside bubbles. The CO₂ gas dependence of Na emission in NaCl aqueous solutions showed a similar change in the line profiles to that in SDS aqueous solutions, which supported this proposition. The unshifted narrow lines are easily affected by foreign gases. The results suggest that the two components originate from different environments around the emitting species, although both of them originate from the gas phase inside bubbles. The generation mechanisms of the two components are discussed.     

Estimation of ultrasound induced cavitation bubble temperatures in aqueous solutions

Mean acoustic cavitation bubble temperatures have been measured in a series of aqueous solutions containing C(1)-C(5) aliphatic alcohols, at 355 kHz. The method relies on the distribution of hydrocarbon product yields produced from the recombination of methyl radicals generated on the thermal decomposition of the alcohols. The mean bubble temperature was found to decrease with increasing concentration of alcohol with the effect being more pronounced the higher the molecular weight (the lower the vapour pressure) of the alcohol. It is shown that the decrease in the temperatures measured correlates very well with an increase in the surface excess of the alcohol, similar to that previously reported for the quenching of sonoluminescence in aqueous solutions containing alcohols [J. Phys. Chem. B 101 (1997) 10845; J. Phys. Chem. B 103 (1999) 9231]. The measured temperatures ranged from 4600+/-200 K at zero alcohol concentration to 2300+/-200 K at 0.5 M t-butanol. The validity of the method is discussed and it is concluded that even though a number of assumptions need to be applied the results appear to indicate that the method gives an accurate measure of the mean bubble temperature.     

Monitoring of transient cavitation induced by ultrasound and intense pulsed light in presence of gold nanoparticles

One of the most important challenges in medical treatment is invention of a minimally invasive approach in order to induce lethal damages to cancer cells. Application of high intensity focused ultrasound can be beneficial to achieve this goal via the cavitation process. Existence of the particles and vapor in a liquid decreases the ultrasonic intensity threshold required for cavitation onset. In this study, synergism of intense pulsed light (IPL) and gold nanoparticles (GNPs) has been investigated as a means of providing nucleation sites for acoustic cavitation. Several approaches have been reported with the aim of cavitation monitoring. We conducted the experiments on the basis of sonochemiluminescence (SCL) and chemical dosimetric methods. The acoustic cavitation activity was investigated by determining the integrated SCL signal acquired over polyacrylamide gel phantoms containing luminol in the presence and absence of GNPs in the wavelength range of 400–500 nm using a spectrometer equipped with cooled charged coupled devices (CCD) during irradiation by different intensities of 1 MHz ultrasound and IPL pulses. In order to confirm these results, the terephthalic acid chemical dosimeter was utilized as well. The SCL signal recorded in the gel phantoms containing GNPs at different intensities of ultrasound in the presence of intense pulsed light was higher than the gel phantoms without GNPs. These results have been confirmed by the obtained data from the chemical dosimetry method. Acoustic cavitation in the presence of GNPs and intense pulsed light has been suggested as a new approach designed for decreasing threshold intensity of acoustic cavitation and improving targeted therapeutic effects.     

Advanced Fenton processing of aqueous phenol solutions: a continuous system study including sonication effects

Our previous report based on a batch reactor system for the Advanced Fenton Process (AFP) showed that pH, hydrogen peroxide and the organic substances treated are among the most important factors affecting the oxidation efficiency. As an extended study towards its potential commercialisation, this paper reports the effects of the main process parameters including those relating to a new laboratory scale AFP flow-through system. In order to systemise and correlate the results, the Taguchi experimental design method was used. Total organic carbon (TOC) removal was utilised as the measure of the oxidation efficiency and it was found that the removal of phenol from aqueous solution at pH 2.0 and 2.5 was very similar but hydrogen peroxide supply significantly affected the TOC removal with the change of flow rate from 14.4 ml/h to 60 ml/h. Also, the initial concentration of phenol was a highly significant factor, with higher concentrations resulting in a lower TOC removal rate. The temperature effects in the range of 14-42 degrees C were investigated and it was found that there was accelerated oxidation of phenol in the early stages but after 90 min there was no significant difference between the results. Sonication with a bath type sonicator resulted in relatively small enhancements of TOC removal but further studies with cup-horn sonication showed that TOC removal increased with higher intensity of sonication.     

Fabrication of oxide base nanostructures using pulsed laser ablation in aqueous solutions

Nanoparticles of TiO₂ and SnO₂ were obtained by laser ablation of Ti and Sn targets in both deionized water and sodium dodecyl sulfate (SDS) solutions. The crystallinity of the nanoparticles strongly depended on the SDS concentration in the solution. Well-crystallized oxide nanoparticles were most abundantly fabricated in SDS solution with around the critical micelle concentration. An inorganic/organic layered nanocomposite consisting of a zinc hydroxide layer and a SDS lamellar interlayer was obtained by the ablation of Zn in SDS solutions. The oxide and/or hydroxide can be formed by the rapid reactive quenching with water in the liquid–plasma interface, where ablated species can be oxidized by aqueous oxidation. The surfactant in the liquid medium could affect the aggregation and growth of nuclei after the oxidation. The preparation of Pt/TiO₂ nanocomposite particles by PLA of the bi-combinant target of Pt and TiO₂ is also reported. PACS 81.16.Mk; 81.10.Dn; 81.07.Bc     

Effect of exposure parameters on cavitation induced by low-level dual-frequency ultrasound

In order to quantify the effects of exposure parameters under therapeutic conditions such as sonodynamic therapy, it is necessary initially to evaluate the inertial cavitation activity in vitro. In this study, the dependence of cavitation activity induced by the low-level dual-frequency ultrasound irradiation on exposure parameters has been studied. Experiments were performed in the near 150 kHz and 1 MHz fields in the progressive wave mode. It has been shown that at constant ultrasound energy the fluorescence intensity for continuous sonication is higher than for pulsed mode. With increasing the duty cycle of pulsed field, the inertial cavitation activity is increased. The activity of cavitation produced by simultaneous combined sonication by two ultrasound fields is remarkably higher than the algebraic sum of effects produced by fields separately (p-value < 0.05). This study shows that simultaneous combined dual-frequency ultrasound sonication in continuous mode is more effective in producing inertial cavitation activity at low-level intensity. Therefore, it is concluded that investigations in this combined ultrasound sonication can be useful in sonodynamic therapy for superficial tumors.     

Stability and energy efficiency of pulsed corona discharge in treatment of dispersed high-conductivity aqueous solutions

Pulsed corona discharge (PCD) is an energy-efficient method of water treatment, although its instability in treatment of conductive solutions showered onto the electrodes presents a problem. The impact of conductivity and gaseous ozone concentration on the discharge stability and the energy transfer efficiency was established. The discharge was stabilized by adjusting the voltage pulse shape. Energy dissipation increases with the treated solution conductivity due to ohmic losses reaching 30% of the energy delivered to the reactor at 45 mS cm⁻¹. The PCD energy efficiency and safety was improved by the modified electrode system design reducing the losses.     

Coumarin fluorometry to quantitatively detectable OH radicals in ultrasound aqueous medium

When ultrasound (US) was exposed to aqueous coumarin solution in air atmosphere, the UV–visible and fluorescence spectra of the probe were measured at different US exposure times. The US exposure was carried out at 43 kHz and 500 kHz with different out-put power. It was found that the 500 kHz US produced umbelliferone fluorescence, while the 43 kHz US had no fluorescence. In addition, the coumarin absorbance at 270 nm maximum was decreased with in cases of the US exposure time. In contrary, the fluorescent intensity of umbelliferone at 460 nm increased with increasing of US exposure time. This exhibited that the coumarin probe was converted to umbelliferone by the US exposure, when the 500 kHz US was operated. This was facted that the coumarin framework was caused with addition of OH groups which was generated by the 500 kHz US. Therefore, the umbelliferone fluorescent became a probe to estimate OH radical in US medium. Furthermore, the chemo-fluorometry showed that the emission maximum of the formed umbelliferone could probe the bulk pHs in the US aqueous medium.     

Dual effects of ultrasound on fabrication of anodic aluminum oxide

Ultrasound has been proven to enhance the mass transfer process and impact the fabrication of anodic aluminum oxide (AAO). However, the different effects of ultrasound propagating in different media make the specific target and process of ultrasound in AAO remain unclear, and the effects of ultrasound on AAO reported in previous studies are contradictory. These uncertainties have greatly limited the application of ultrasonic-assisted anodization (UAA) in practice. In this study, the bubble desorption and mass transfer enhancement effects were decoupled based on an anodizing system with focused ultrasound, such that the dual effects of ultrasound on different targets were distinguished. The results showed that ultrasound has the dual effects on AAO fabrication. Specifically, ultrasound focused on the anode has a nanopore-expansion effect on AAO, leading to a 12.24 % improvement in fabrication efficiency. This was attributed to the promotion of interfacial ion migration through ultrasonic-induced high-frequency vibrational bubble desorption. However, AAO nanopores were observed to shrink when ultrasound was focused on the electrolyte, accompanied by a 25.85 % reduction in fabrication efficiency. The effects of ultrasound on mass transfer through jet cavitation appeared to be the reason for this phenomenon. This study resolved the paradoxical phenomena of UAA in previous studies and is expected to guide AAO application in electrochemistry and surface treatments.     

Synergistic effects of the alternating application of low and high frequency ultrasound for particle synthesis in microreactors

Ultrasound (US) is a promising method to address clogging and mixing issues in microreactors (MR). So far, low frequency US (LFUS), pulsed LFUS and high frequency US (HFUS) have been used independently in MR for particle synthesis to achieve narrow particle size distributions (PSD). In this work, we critically assess the advantages and disadvantages of each US application method for the case study of calcium carbonate synthesis in an ultrasonic microreactor (USMR) setup operating at both LFUS (61.7 kHz, 8 W) and HFUS (1.24 MHz, 1.6 W). Furthermore, we have developed a novel approach to switch between LFUS and HFUS in an alternating manner, allowing us to quantify the synergistic effect of performing particle synthesis under two different US conditions. The reactor was fabricated by gluing a piezoelectric plate transducer to a silicon microfluidic chip. The results show that independently applying HFUS and LFUS produces a narrower PSD compared to silent conditions. However, at lower flow rates HFUS leads to agglomerate formation, while the reaction conversion is not enhanced due to weak mixing effects. LFUS on the other hand eliminates particle agglomerates and increases the conversion due to the strong cavitation effect. However, the required larger power input leads to a steep temperature rise in the reactor and the risk of reactor damage for long-term operation. While pulsed LFUS reduces the temperature rise, this application mode leads again to the formation of particle agglomerates, especially at low LFUS percentage. The proposed application mode of switching between LFUS and HFUS is proven to combine the advantages of both LFUS and HFUS, and results in particles with a unimodal narrow PSD (one order of magnitude reduction in the average size and span compared to silent conditions) and negligible rise of the reactor temperature.     

New insights into the ultrasound impact on covalent reactions of myofibrillar protein

In this work, two different covalent reactions, namely, alkaline reaction and free radical oxidation, were selected to compare the difference in the strengthening effects of ultrasound treatment (UDT). The grafting effects were verified by protein electrophoresis and bound gallic acid (GA) assay. Furthermore, non-covalent interactions between myofibrillar protein (MPN) aggregates were destroyed by UDT, as proved by the lower particle sizes and higher ζ-potential. Comparatively, the results from tertiary structure index and circular dichroism revealed UDT-assisted free radical oxidation could lead to better conjugates with greater structural properties. The atomic force microscope (AFME) and protein flexibility showed that MPNs appeared to display as irregular spherical particles after alkaline reaction, however, maintained fibrous structure during the free radical oxidation. Consequently, the combination of UDT and free radical oxidation were more effectively for strengthening the influence of acoustic cavitation on MPNs, of which mechanism was the changes in viscosity properties, microstructure and acoustic cavitation radicals.     

Understanding the effects of mineral water matrix on degradation of several pharmaceuticals by ultrasound: Influence of chemical structure and concentration of the pollutants

Degradation of seven relevant pharmaceuticals with different chemical structures and properties: acetaminophen (ACE), cloxacillin (CXL), diclofenac (DCF), naproxen (NPX), piroxicam (PXC), sulfacetamide (SAM) and cefadroxil (CDX), in distilled water and mineral water by ultrasound was studied herein. Firstly, proper conditions of frequency and acoustic power were determined based on the degradation ability of the system and the accumulation of sonogenerated hydrogen peroxide (24.4 W and 375 kHz were found as the suitable conditions for the sonochemical treatment of the pharmaceuticals). Under such conditions, the pharmaceuticals degradation order in distilled water was: PXC > DCF ~ NPX > CXL > ACE > SAM > CDX. In fact, the initial degradation rate showed a good correlation with the Log P parameter, most hydrophobic compounds were eliminated faster than the hydrophilic ones. Interestingly, in mineral water, the degradation of those hydrophilic compounds (i.e., ACE, SAM and CDX) was accelerated, which was attributed to the presence of bicarbonate ions. Afterwards, mineral water containing six different initial concentrations (i.e., 0.331, 0.662, 3.31, 16.55, 33.1, and 331 µM) of selected pharmaceuticals was sonicated, the lowest concentration (0.331 µM) always gave the highest degradation of the pollutants. This result highlights the great ability of the sonochemical process to treat bicarbonate-rich waters containing pollutants at trace levels, as pharmaceuticals. Finally, the addition of ferrous ions to the sonochemical system to generate a sono-Fenton process resulted in an acceleration of degradation in distilled water but not in mineral water. This was attributed to the scavenging of sonogenerated HO• by bicarbonate anion, which decreases H₂O₂ accumulation, thus limiting the Fenton reaction.     

空化水中HO2自由基的测定

采用频率为1．8MHz,声强为1－5W／cm2的超声波引发水中的空化效应,通过采用吡啶溶液作为HO2自由基捕获剂,测出了实验条件下空化水中HO2自由基的浓度水平为10－5M。