Luminescence properties of nanoparticles synthesized in electric discharge in liquid under ultrasonic cavitation

The differences in the luminescence intensity of metal oxide nanoparticles synthesized in electric discharges in liquidmedia under intense ultrasonic vibrations in the absence and presence of cavitation are studied.     

Effect of ultrasonic cavitation on dynamics and characteristics of electric discharge in liquid

Characteristics of electric discharges in liquid media under intense ultrasonic vibrations are studied. The difference in current dynamics and discharge voltages in the presence and in the absence of cavitation is shown.     

On the discharge in laser plasma in an external electric field

The possibility of creating discharge in laser plasma in an external electric field with quasi-static current generation along the field is discussed. The knowledge of the quasi-static current generation mechanism in laser plasma, associated with the rarefaction shock wave (RSW), allows the determination of the spatial distribution of these currents during laser irradiation of a planar target. Having included the (planar or cylindrical) target into an external contour, we propose a discharge scheme in laser plasma, where the discharge current increases during the laser pulse.     

Nanoscale metal oxide particles produced in the plasma discharge in the liquid phase upon exposure to ultrasonic cavitation. 1. Method for producing particles

It is shown that a new form of the plasma discharge with bulk glow throughout the space between electrodes and an descending current-voltage characteristic, occurring in liquid in an ultrasonic field with an intensity above the cavitation threshold, can be efficiently used to initiate the various physical and chemical processes. In such an acoustic plasma discharge, nanoparticles of oxides of various metals, i.e., aluminum, copper, tin, iron, titanium, indium, zinc, molybdenum, and others, are synthesized with controllable particle shape and size and narrow size distribution. Micrographs of some nanoparticles are presented. The difference in luminescence of particles produced in the absence and presence of cavitation is shown.     

Nanoscale metal oxide particles produced in the plasma discharge in the liquid phase upon exposure to ultrasonic cavitation. 3. Optical nonlinearities of particle suspensions

The nonlinear response of metal oxide nanoparticles obtained by the acoustic plasma method is measured in aqueous disperse systems at a wavelength of 532 nm. Induced absorption is detected in the Cu₂O, WO₃, and ZnO disperse systems, and bleaching is detected in the Fe₂O₃ system. The real and imaginary parts of nonlinear third-order susceptibilities are determined.     

The influence of high electric field strengths on the electric current in liquid benzene

The electric conductivity in the field strength range between 2 kV/cm and 110 kV/cm and the time dependence of the current after voltage application have been studied.     

Nanoscale metal oxide particles produced in the plasma discharge in the liquid phase upon exposure to ultrasonic cavitation. 2. Sizes and stability. Dynamic light scattering study

Size distributions of tungsten oxide particles produced in the plasma discharge in the liquid phase upon exposure to ultrasound were studied by the dynamic light scattering method. Particles produced by this method under ultrasonic cavitation (USC), in the absence of cavitation, and without cavitation followed by ultrasonic processing are compared. The behavior of concentrations of particles of various size groups is comparatively estimated by the data on particle sizes and scattering intensity using the Rayleigh-Gans-Debye approximation. It is shown that ultrasonic processing improves the aggregative stability of suspension; in a suspension of particles produced under USC, large aggregates eventually decay into individual small particles.     

Surface flow of liquid in an electric field

An analytic solution is proposed for a model problem which demonstrates the occurrence of a surface flow of weakly conducting liquid in an electric field which was previously observed experimentally by the author. Zh. Tekh. Fiz. 69, 127–128 (June 1999)     

Synthesis of nanoparticles using a pulsed electrical discharge in a liquid

We used a pulsed electrical discharge in a liquid to obtain Cu-, WC-, and ZnO-containing nanoparticles. The effect of the discharge current and pulse duration on the morphology and phase composition of the synthesized material was studied by spectrophotometry, transmission electron microscopy, and x-ray diffraction analysis. We discuss possible mechanisms for nanoparticle formation in a discharge submerged in a liquid. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 111–120, January–February, 2008.     

Polarization diagnostics of plasma in an electric field

A polarization diagnostics method for Stark states is presented, and it is applied to determining the electric field in a plasma. The theoretical basis of the method is given and the latter is compared with other spectroscopic methods. An apparatus is described for measuring the polarization characteristics of plasma radiation from pulsed discharges. Measurements were made in a beam-type plasma of the relative intensities of the =3964 and 4911 Å allowed and forbidden helium lines and of their degree of linear polarization. The results of the measurements were used to calculate the electric field distribution in the accelerating gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 26–33, January, 1995.     

Behaviour of nematic liquid crystals doped with ferroelectric nanoparticles in the presence of an electric field

A planar nematic liquid crystal cell (NLC) doped with spherical ferroelectric nanoparticles is considered. Polarisation of the nanoparticles are assumed to be along the NLC molecules parallel and antiparallel to the director with equal probability. The NLC molecules anchoring to the cell walls are considered to be strong, while soft anchoring at the nanoparticles surface is supposed. Behaviour of the NLC molecules and nanoparticles in the presence of a perpendicular electric field to the NLC cell is theoretically investigated. The electric field of the nanoparticles is taken into account in the calculations. Freedericksz transition (FT) threshold field in the presence of nanoparticles is found. Then, the director and particles reorientations for the electric fields larger than the threshold field are studied. Measuring the onset of the nanoparticles reorientation is proposed as a new method for the FT threshold measurement.     

Numerical investigation of cavitation generated by an ultrasonic dental scaler tip vibrating in a compressible liquid

Bacterial biofilm accumulation around dental implants is a significant problem leading to peri-implant diseases and implant failure. Cavitation occurring in the cooling water around ultrasonic scaler tips can be used as a novel solution to remove debris without any surface damage. However, current clinically available instruments provide insufficient cavitation around the activated tip surface. To solve this problem a critical understanding of the vibro-acoustic behaviour of the scaler tip and the associated cavitation dynamics is necessary. In this research, we carried out a numerical study for an ultrasound dental scaler with a curved shape tip vibrating in water, using ABAQUS based on the finite element method. We simulated the three-dimensional, nonlinear and transient interaction between the vibration and deformation of the scaler tip, the water flow around the scaler and the cavitation formation and dynamics. The numerical model was well validated with the experiments and there was excellent agreement for displacement at the free end of the scaler. A systematic parametric study has been carried out for the cavitation volume around the scaler tip in terms of the frequency, amplitude and power of the tip vibration. The numerical results indicate that the amount of cavitation around the scaler tip increases with the frequency and amplitude of the vibration. However, if the frequency is far from the natural frequency, the cavitation volume around the free end decreases due to reduced free end vibration amplitude.     

The electrical conductivity of benzene and its monohalide derivatives in an ultrasonic field

Ultrasonics has found increasing use in instrumentation techniques in recent years as a means of studying the physicochemical properties of materials and articles, and also as a means of accelerating technological processes in various branches of the national economy. At the same time not enough use is made of the possibilities of ultrasonics in many branches of science and technology. These include the study of the effect of ultrasonics on the electrical conductivity of electrolytes, liquid semiconductors, and dielectrics. Available published information on these topics [1 – 5] is scant; the effects observed have been described only qualitatively and need further study.The present paper is devoted to a study of the effect of ultrasonic vibrations (frequency 1.25 Mc, intensity 2 W/cm²) on the electrical conductivity of benzene in an electric field of 5 kV/cm, and on the electrical conductivity of chlorobenzene, bromobenzene, and iodobenzene in a field of 1 kV/cm in the precavitation region. An interpretation of the experimental results is offered.     

Synthesis of nanoparticles in an atmospheric pressure glow discharge

Nanopowders are produced in a low temperature, non-equilibrium plasma jet (APPJ), which produces a glow discharge at atmospheric pressure, for the first time. Amorphous carbon and iron nanoparticles have been synthesized from Acetylene and Ferrocene/H₂, respectively. High generation rates are achieved from the glow discharge at near-ambient temperature (40–80°C), and rise with increasing plasma power and precursor concentration. Fairly narrow particle size distributions are measured with a differential mobility analyzer (DMA) and an aerosol electrometer (AEM), and are centered around 30–35 nm for carbon and 20–25 nm for iron. Particle characteristics analyzed by TEM and EDX reveal amorphous carbon and iron nanoparticles. The Fe particles are highly oxidized on exposure to air. Comparison of the mobility and micrograph diameters reveal that the particles are hardly agglomerated or unagglomerated. This is ascribed to the unipolar charge on particles in the plasma. The generated particle distributions are examined as a function of process parameters.     

Harmonic responses and cavitation activity of encapsulated microbubbles coupled with magnetic nanoparticles

Encapsulated microbubbles coupled with magnetic nanoparticles, one kind of hybrid agents that can integrate both ultrasound and magnetic resonance imaging/therapy functions, have attracted increasing interests in both research and clinic communities. However, there is a lack of comprehensive understanding of their dynamic behaviors generated in diagnostic and therapeutic applications. In the present work, a hybrid agent was synthesized by integrating superparamagnetic iron oxide nanoparticles (SPIOs) into albumin-shelled microbubbles (named as SPIO-albumin microbubbles). Then, both the stable and inertial cavitation thresholds of this hybrid agent were measured at varied SPIO concentrations and ultrasound parameters (e.g., frequency, pressure amplitude, and pulse length). The results show that, at a fixed acoustic driving frequency, both the stable and inertial cavitation thresholds of SPIO-albumin microbubble should decrease with the increasing SPIO concentration and acoustic driving pulse length. The inertial cavitation threshold of SPIO-albumin microbubbles also decreases with the raised driving frequency, while the minimum sub- and ultra-harmonic thresholds appear at twice and two thirds resonance frequency, respectively. It is also noticed that both the stable and inertial cavitation thresholds of SonoVue microbubbles are similar to those measured for hybrid microbubbles with a SPIO concentration of 114.7 μg/ml. The current work could provide better understanding on the impact of the integrated SPIOs on the dynamic responses (especially the cavitation activities) of hybrid microbubbles, and suggest the shell composition of hybrid agents should be appropriately designed to improve their clinical diagnostic and therapeutic performances of hybrid microbubble agents.     

The morphologies of Lennard-Jones liquid encapsulated by carbon nanotubes

Using molecular dynamics simulations, we studied the morphologies of Lennard-Jones liquid encapsulated in carbon nanotubes (CNTs) for a wide range of liquid–CNT interaction, system size and temperature. The morphology of liquid is found to be sensitive to the filling ratio of liquid (a ratio of liquid volume to the available volume of CNT pore) and the liquid–CNT interaction. The ‘phase diagram’, namely by the morphologies versus the liquid–CNT interaction and the filling ratio, is obtained. In most cases, the liquid inside CNTs forms a thin liquid shell attached to a carbon wall when the filling ratio is small. With the increasing of the filling ratio, liquid tends to form droplet. As the filling ratio increases further, liquids form a cylinder with finite length. Finally, the whole inner space of CNT was filled with liquid when the filling ratio is large enough. Current studies could shed light on the adsorption and flow of liquid inside CNTs.     

Preparation and structure of carbon encapsulated copper nanoparticles

Carbon-encapsulated copper nanoparticles were synthesized by a modified arc plasma method using methane as carbon source. The particles were characterized in detail by transmission electron microscope, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray diffraction, thermogravimetric and differential scanning calorimetry. The encapsulated copper nanoparticles were about 30 nm in diameter with 3–5 nm graphitic carbon shells. The outside graphitic carbon layers effectively prevented unwanted oxidation of the copper inside. The effect of the ratio of He/CH₄ on the morphologies and the formation of the carbon shell were investigated.     

声场与电场作用下空化泡的动力学特性

以液体为工作介质, 利用空化泡的RP控制方程, 模拟分析了无量纲化的电场频率、场强的幅值以及无量纲化的声波频率、 声压幅值的变化对空化泡运动特性的影响. 结果表明: 声场和电场联合作用时, 空化泡运动处于混沌区域范围远高于两者单独作用下空化泡的混沌区域范围. 这不仅对声空化的进一步研究具有重要的理论意义, 而且对于提高和改进空化降解有机污染物的技术也具有指导意义.     

Investigation of noninertial cavitation produced by an ultrasonic horn

This paper reports on noninertial cavitation that occurs beyond the zone close to the horn tip to which the inertial cavitation is confined. The noninertial cavitation is characterized by collating the data from a range of measurements of bubbles trapped on a solid surface in this noninertial zone. Specifically, the electrochemical measurement of mass transfer to an electrode is compared with high-speed video of the bubble oscillation. This gas bubble is shown to be a "noninertial" event by electrochemical surface erosion measurements and "ring-down" experiments showing the activity and motion of the bubble as the sound excitation was terminated. These measurements enable characterization of the complex environment produced below an operating ultrasonic horn outside of the region where inertial collapse can be detected. The extent to which solid boundaries in the liquid cause the frequencies and shapes of oscillatory modes on the bubble wall to differ from their free field values is discussed.