Study of acoustic parameters of binary mixtures of a nonpolar liquid with polar liquid at different frequencies

The densities (ρ) and ultrasonic velocities (C) of binary mixture of diisopropyl ether (DIPE) and bromobenzene (BB) have been measured at different frequencies (1 MHz, 3 MHz and 5 MHz) over the entire range of mole fraction of diisopropyl ether (DIPE) at temperature 303 K. The intermolecular free length (L _f ), isentropic compressibility (β), acoustic impedance (Z) and excess values of isentropic compressibility (β ^E ) and acoustic impedance (Z^E) have been computed using values of ultrasonic velocity (C) and density (ρ). The ultrasonic velocity, intermolecular free length are positive whereas the excess values of isentropic compressibility and acoustic impedance are negative over the entire composition range of DIPE which indicates presence of specific interactions between unlike molecules. The results are discussed in the light of intermolecular interactions occurring in the mixtures.      

The influence of pressure on the acoustic cavitation in saturated CO2-expanded N,N-dimethylformamide

CO₂-expanded organic solvent is a kind of important fluid medium and has broad applications in chemical industry, environmental protection and other fields. Ultrasonic cavitation in gas expanded liquids (GXLs) is conducive to enhancing mass transfer and producing many exciting phenomena. In this paper, the ultrasonic cavitations and streaming in the saturated CO₂-expanded liquid N, N-dimethylformamide (DMF) at 4.2 MPa and 5.2 MPa are observed by a high-speed camera. The cavitation intensity and time trace of pressure pulses are recorded using a PZT hydrophone. The influences of gas–liquid equilibrium pressure and ultrasonic power on the cluster dynamics of transient and stable cavitation are examined. The excess molar enthalpies required for CO₂ dissociation from DMF are calculated by Peng-Robinson equations of state and the change of surface free energy of CO₂-expanded DMF is predicted. The results show that the excess enthalpy of the mixture is one of the key factors to control ultrasonic cavitation at high pressurized conditions, while the surface tension is the key factor for low pressure. As the increase of applied ultrasonic power, the formation and collapsing frequency of bubble clusters increases, and the amplitude and cyclic frequency of pressure pulse are enhanced. The transient cavitation intensity increases as it reaches a maximum value at a certain ultrasonic power and then decreases. The change trends of stable cavitation intensity under different pressures are basically same. It can be concluded from the evidence that ultrasonic cavitation in CO₂-expanded DMF is affected by the combined effect of compression and substitution: compression depresses the nucleation and growth of bubbles, while the high solubility of CO₂ in DMF is conducive to the generation of bubbles in cavitation.     

Prediction of ultrasonic velocity and intermolecular free-length and their correlation with interaction in binary liquid mixtures

The ultrasonic velocities of binary liquid mixtures of 1,1,2,2-tetrachloroethane with benzene, toluene,p-xylene, acetone and cyclohexane have been evaluated at 298.15 and 308.15 K using Schaaff’s collision factor theory (CFT), Jacobson’s free length theory (FLT), Nomoto’s relation and Van Dael ideal mixing relation. The ideal mixing relation gives the minimum deviation for all the systems except with acetone. The intermolecular free length has also been evaluated using ultrasonic and thermodynamic methods and the limitations of both the methods have been discussed. The deviations in ultrasonic velocity and intermolecular free length are discussed in terms of weak interaction between unlike molecules.     

Free surface entrainment of oxide particles and their role in ultrasonic treatment performance of aluminum alloys

Although the ultrasonic treatment of molten aluminum has been studied for long period, there is still much to be revealed for this process. Many studies have focused on the investigation of acoustic cavitation and streaming under the horn tip and their effects on the treatment efficiency. However, to the best of our knowledge, no attempt has been done to explain phenomena occurring near or on the melt free surface. Thus, the goal of this study is to investigate phenomena occurring at the free surface during ultrasound irradiation and clarify their possible influence on the ultrasound treatment performance. The results of high temperature and water model experiments reveal that ultrasound irradiation significantly promotes the formation of alumina particles on the melt free surface around sonotrode, and part of these particles can be entrained into aluminum melts. Furthermore, TEM observation results suggested that the entrained alumina inclusions can serve as nucleation sites for the primary Al₃Zr compounds. Most importantly, the oxidation and entrainment of particles from free surface are likely to be controllable by the immersion depth of sonotrode into molten aluminum.     

MnO2/CeO2 for catalytic ultrasonic degradation of methyl orange

Catalytic ultrasonic degradation of aqueous methyl orange was studied in this paper. Heterogeneous catalyst MnO₂/CeO₂ was prepared by impregnation of manganese oxide on cerium oxide. Morphology and specific surface area of MnO₂/CeO₂ catalyst were characterized and its composition was determined. Results showed big differences between fresh and used catalyst. The removal efficiency of methyl orange by MnO₂/CeO₂ catalytic ultrasonic process was investigated. Results showed that ultrasonic process could remove 3.5% of methyl orange while catalytic ultrasonic process could remove 85% of methyl orange in 10 min. The effects of free radical scavengers were studied to determine the role of hydroxyl free radical in catalytic ultrasonic process. Results showed that methyl orange degradation efficiency declined after adding free radical scavengers, illustrating that hydroxyl free radical played an important role in degrading methyl orange. Theoretic analysis showed that the resonance size of cavitation bubbles was comparable with the size of catalyst particles. Thus, catalyst particles might act as cavitation nucleus and enhance ultrasonic cavitation effects. Measurement of H₂O₂ concentration in catalytic ultrasonic process confirmed this hypothesis. Effects of pre-adsorption on catalytic ultrasonic process were examined. Pre-adsorption significantly improved methyl orange removal. The potential explanation was that methyl orange molecules adsorbed on catalysts could enter cavitation bubbles and undergo stronger cavitation.     

Characterization of wheat-flour-water doughs: a new method using ultrasound

In this paper, an original method of evaluating the physical properties of wheat-flour-water systems using high-frequency low-power ultrasound is presented. Most of the experiments were performed with a reflectance technique measuring the acoustic impedance of doughs. The velocity of propagation, attenuation and viscoelastic moduli have been evaluated for both compressional and shear ultrasonic waves in the interval 2-10 MHz for doughs of different hydrations. The 53% water content was found to be critical with respect to the presence of free water. The influence of the mixing and rest times on the longitudinal ultrasonic parameters is also studied.     

Wetting process of electrolyte in high density Cu/Sn micro-bumps electrodepositing

Wetting process of electrolyte in high density Cu/Sn micro-bumps electrodepositing is reported in this paper. Three methods were adopted to enable electrolyte to permeate photo-etching micro-holes with high aspect ratio, including plasma treatment, adding wetting additive in electrolyte and mechanical action. Wettability of the samples with electrolyte was improved by the first two methods, according to contact angle and surface tension measurement. However, electrolyte still cannot reach up to the bottom of micro-hole. And then, electrolyte was subjected to mechanical action, including agitation and ultrasonic vibration. Under mechanical action, void free Cu/Sn micro-bumps fabrication was achieved in photo-etching micro-holes with depth of 60 μm and radius of 30 μm. At last, we proposed a model to show wetting process of electrolyte in photo-etching micro-holes.     

Ultrasonic and infrared study of molecular interactions in ternary mixtures of 1-naphthol and 2-naphthol with 2-propanone in benzene

The measurements of ultrasonic velocity and density were made for the ternary mixtures of l-naphthol/2-naphthol with 2-propanone in benzene at 20, 30 and 40°C in the mole fraction range of 0.00 to 0.05. Adiabatic compressibility and intermolecular free length have been evaluated using ultrasonic velocity data. The non-linear variation of ultrasonic velocity and allied parameters with mole fraction indicates solute-solute interactions through hydrogen bonding between unlike molecules. Results of ultrasonic velocity and density measurements are further supported by FT-IR spectra. The change in transmittance as well as the shift in the frequency of the representative peak of the OH stretching in FT-IR spectra give inferences about the complex formation.     

Synthesis and Properties of Cupric Sulphate Doped Polyvinyl Pyrrolidone (PVP) Solutions

The optical, electrical and acoustical properties of polymer solutions based on polyvinyl pyrrolidone (PVP) doped with cupric sulphate (CuSO₄) were studied. The polymer solutions were prepared by varying the concentration of Cu in the PVP using a simple chemical route. The UV-visible spectroscopy results showed that the optical absorbance decreased with an increase in wavelength from 300 to 700 nm. The optical band gaps were found to decrease with addition of the Cu salt in the polymer. The refractive index also showed significant variation with the doping of the CuSO₄. The electrical conductivity of the polymer solutions was found to increase with temperature as well as concentration of Cu while the activation energy of electrical conduction decreased with concentration of Cu. The ultrasonic velocities of the polymer solutions were measured at a frequency of 1 MHz using an ultrasonic interferometer. The ultrasonic velocity and surface tension were increased while the adiabatic compressibility, acoustic impedance and intermolecular free length, the average distance between the surfaces of the coils of adjacent molecules, were decreased with increase in the concentration of CuSO₄ in the PVP.     

非线性电磁超声对铝合金拉伸变形评价研究

非线性系数是描述材料中微纳尺度损伤的特征参量,非线性系数常通过接触式压电超声进行检测,但耦合剂引起的非线性一般是未知的,针对这一问题,提出了一种非接触式电磁超声非线性纵波检测方法。该方法基于洛伦兹力机理在试件表面产生的振动弹性波,利用不同拉伸载荷下所制备的损伤试件,分别利用压电超声、电磁超声进行非线性超声系数测量。实验结果表明:利用两种非线性超声检测的相对非线性系数与铝合金的拉伸形变呈单调关系,同时也论证了电磁超声纵波基于非线性理论对塑性变形评估的可行性。      

Effect of frequency on acoustic parameters in a binary mixture of polar liquids

The densities (α) and ultrasonic velocities (C) of binary mixtures of a polar liquid like acetone and toluene have been measured at different frequencies (lMHz, 3MHz and 5MHz) over the entire range of mole fraction of acetone at temperature 303.16k. The intermolecular free length (L _f ), isentropic compressibility (β), acoustic impedance (Z), excess values of isentropic compressibility (β ^E ) and acoustic impedance (Z ^E ) have been computed using values of ultrasonic velocity (C) and density (α). The ultrasonic velocity (C), intermolecular free length (L _f ) and excess values of isentropic compressibility are positive whereas excess values of acoustic impedance is negative for the entire composition range which indicates the specific interaction between unlike molecules. The results are discussed in the light of intermolecular interactions occurring in the solutions.     

Degradation,isomerization and stabilization of three dicaffeoylquinic acids under ultrasonic treatment at different pH

Dicaffeoylquinic acids (diCQAs) are found in a variety of edible and medicinal plants with various biological activities. An important issue is the low stability of diCQAs during extraction and food processing, resulting in the degradation and transformation. This work used 3,5-diCQA as a representative to study the influence of different parameters in ultrasonic treatment on the stability of diCQAs, including solvent, temperature, treatment time, ultrasonic power, duty cycle, and probe immersion depth. The generation of free radicals and its influence were investigated during the treatment. The stability of three diCQAs (3,5-diCQA, 4,5-diCQA and 3,4-diCQA) under the certain ultrasonic condition at different pH conditions was evaluated and found to decrease with the increase of pH, further weakened by ultrasonic treatment. Ultrasound was found to accelerate the degradation and isomerization of diCQAs. Different diCQAs showed different pattern of degradation and isomerization. The stability of diCQAs could be improved by adding epigallocatechin gallate and vitamin C.     

A Technical Critique of Some Parts of the Free Energy Principle

We summarize the original formulation of the free energy principle and highlight some technical issues. We discuss how these issues affect related results involving generalised coordinates and, where appropriate, mention consequences for and reveal, up to now unacknowledged, differences from newer formulations of the free energy principle. In particular, we reveal that various definitions of the “Markov blanket” proposed in different works are not equivalent. We show that crucial steps in the free energy argument, which involve rewriting the equations of motion of systems with Markov blankets, are not generally correct without additional (previously unstated) assumptions. We prove by counterexamples that the original free energy lemma, when taken at face value, is wrong. We show further that this free energy lemma, when it does hold, implies the equality of variational density and ergodic conditional density. The interpretation in terms of Bayesian inference hinges on this point, and we hence conclude that it is not sufficiently justified. Additionally, we highlight that the variational densities presented in newer formulations of the free energy principle and lemma are parametrised by different variables than in older works, leading to a substantially different interpretation of the theory. Note that we only highlight some specific problems in the discussed publications. These problems do not rule out conclusively that the general ideas behind the free energy principle are worth pursuing.     

A new development of dyestuffs degradation system using ultrasound

Dyestuffs are often present in industrial wastewaters and can consist of hazardous substances which have a serious impact on the environment and personal health. This report describes a system developed to degrade these substances using sonochemical reactions. Ultrasonic frequencies of 118, 224, 404 and 651 kHz and power input values of 11.4, 29.0 and 41.5 W were tested on Rhodamine B and Orange II dyestuff solutions in order to find the best degradation conditions. The ultrasonic irradiation of air-saturated solutions produces free radicals that combine and generates hydrogen peroxide, and compared to the production of hydrogen peroxide when irradiating water, a decrease was found during the irradiation to dyestuff solutions, indicating that some of the free radicals were consumed in the dyestuffs degradation process. The effects of the ultrasonic irradiation conditions on the pH, nitric and nitrous acid formations as well as the total organic carbon value (TOC) were also investigated. For the ultrasonic frequencies of 224, 404 and 651 kHz, the degradation rates were very similar, however, the 118 kHz system presented a degradation rate of about one-third that of the higher frequencies for both dyestuffs. The Rhodamine B solutions were decolorized within 2 h of ultrasonic irradiation for all systems with the exception of the 118 kHz one. For Orange II, except for the 118 kHz system, all solutions were decolorized within 4 h of ultrasonic irradiation. All reactions were carried out at 25 degrees C and the total ultrasonic irradiation time was 10 h.     

Study of intermolecular interactions in binary mixtures of 2′-chloro-4-methoxy-3-nitro benzil in various solvents and at different concentrations by the measurement of acoustic properties

Density (ρ), ultrasonic velocity (u), adiabatic compressibility (β), apparent molar volume (Ø), acoustic impedance (Z), intermolecular free length (L_f), relative association (RA) of binary mixtures of 2′-chloro-4-methoxy-3-nitro benzil (abbreviated as 2CBe) in ethanol, acetonitrile, chloroform, dioxane and benzene were measured at different concentrations at 298 K. Several useful parameters such as excess density, excess ultrasonic velocity, excess adiabatic compressibility, excess apparent molar volume, excess acoustic impedance and excess intermolecular free length have been calculated. These parameters are used to explain the nature of intermolecular interactions taking place in the binary mixture. The above study is useful in understanding the solute – solvent interactions occurring in different concentrations at room temperature.     

Erosion of frozen-gas films by MeV ions

Abstract

The free defect survival ratio is calculated by “cascade-annealing” computer simulation using MARLOWE and modified DAIQUIRI codes in various cases of PKA spectra. The number of subcascades is calculated by “cut-off” calculation using MARLOWE. The adequacy of these methods is checked by comparing the results with experiments (surface segregation measurements and TEM cascade defect observations). The correlation using the weighted average recoil energy as a parameter shows that the saturation of the free defect survival ratio at high PKA energies has a close relation to the cascade splitting into subcascades.     

微液滴在不同能量表面上润湿状态的分子动力学模拟

微小液滴在不同能量表面上的润湿状态对于准确预测非均相核化速率和揭示界面效应影响液滴增长微观机理具有重要意义. 通过分子动力学模拟, 研究了纳米级液滴在不同能量表面上的铺展过程和润湿形态. 结果表明, 固液界面自由能随固液作用强度增加而增加, 并呈现不同液滴铺展速率和润湿特性. 固液作用强度小于1.6的低能表面呈现疏水特征, 继续增强固液作用强度时表面变为亲水, 而固液作用强度大于3.5的高能表面上液体呈完全润湿特征. 受微尺度条件下非连续、非对称作用力影响, 微液滴气液界面存在明显波动, 呈现与宏观液滴不同的界面特征. 统计意义下, 微小液滴在不同能量表面上铺展后仍可以形成特定接触角, 该接触角随固液作用强度增加而线性减小, 模拟结果与经典润湿理论计算获得的结果呈现相似变化趋势. 模拟结果从分子尺度为核化理论中的毛细假设提供了理论支持, 揭示了液滴气液界面和接触角的波动现象, 为核化速率理论预测结果和实验测定结果之间的差异提供了定性解释.     

Ionic conductivity of PVdF-co-HFP/LiClO4 in terms of free volume defects probed by positron annihilation lifetime spectroscopy

ABSTRACT

Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO₄ salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1?Hz to 20?MHz and at different temperatures from 273 to 373?K.

The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373?K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO₄ and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.     

Sonochemistry of degrading p-chlorophenol in water by high frequency ultrasound

The degradation process and mechanism of p-chlorophenol in water using high frequency ultrasound (1.7 mHz) was investigated in this paper. The p-chlorophenol was degraded successfully in the high frequency ultrasonic device with low consumption of energy. The degradation effect was improved by increasing the solution concentration. No products or intermediate products were detected in the reaction mixture by the analytic methods of MS and 1H-NMR after ultrasonic irradiation. The dominant degradation mechanism is high temperature pyrolysis in ultrasonic cavities rather than free radical oxidation, and the experimental results can be explained completely according to pyrolysis mechanism.     

Vibration analysis of ultrasonic tubular resonators

The frequency equation of the axisymmetric coupled vibration of a ultrasonic tubular resonator with both ends free is derived by an exact solution method,based on classical Fl(u|¨)gge thin shell theory.The dependence of the dinieiisionless frequencyΩon the ratio of length to radius l/a.the ratio of radius to thickness a/h and Poisson’s ratio v is investigated, and the axisymmetric coupled vibration of the ultrasonic tubular resonator with both ends shear diaphragm is compared with that with both ends free.The accuracy of two-dimensional and three-dimensional apparent elasticity method is also assessed by the comparison with the exact solution method.Finally,the mode shapes of the ultrasonic tubular resonator are calculated by the exact solution method,and its transform efficient is analyzed.The results show that as for two boundary conditions of both ends free and both ends shear diaphragm,the difference of the effect of the boundary conditions on the dinieiisionless frequency of the axisymmetric coupled vibration of the ultrasonic tubular resonator becomes smaller as l/a increases,and the larger a/h.the smaller the difference.Moreover,for free-free boundary conditions,the change of a/h has nearly no effect on the dinieiisionless frequency of the thin tubular resonator usually considered to mean a/h > 10.Furthermore,the dinieiisionless frequency fi decreases as v increases for a given l/a.and the impact of v onΩis different for different l/a.and the maximum impact will appear when l/a =π.Finally,the study also shows the three-dimensional apparent elasticity method has very high accuracy.