Electric sonic amplitude

In classical electrokinetic phenomena, the forces and fluxes are independent of time. Electroacoustic effects are analogs of electrophoresis and sedimentation potential in which the forces and fluxes are variable in time. Alternating forces induce alternating fluxes of the same frequency, with a time delay. The phenomenological coefficients between the force and coupled flux can be used to calculate the potential. The phase shift is a source of additional information about the system. The electric sonic amplitude (ESA) is the amplitude of the ultrasonic field... 

Electroacoustics — Ultrasound passing through a colloidal dispersion forces the colloidal particles to move back and forth, which leads to a displacement of the double layer around the particles with respect to their centers, and thus induces small electric dipoles. The sum of these dipoles creates a macroscopic AC voltage with the frequency of the sound waves. The latter is called the Colloid Vibration Potential (CVP) [i]. The reverse effect is called Electrokinetic Sonic Amplitude (ESA) effect [ii]. See also Debye effect. 

The dynamic electrophoretic mobility of colloidal particles in an applied oscillating electric field plays an essential role in analyzing the results of electroacoustic measurements of colloidal dispersions, that is, colloid vibration potential (CVP) and electrokinetic sonic amplitude (ESA) measurements [1-20]. This is because CVP and ESA are proportional to the dynamic electrophoretic mobility of colloidal particles. In this chapter, we develop a theory of the dynamic electrophoretic mobility of soft particles in dilute suspensions [21]. 

Electrokinetic sonic amplitude a.c. electric field particles liquid ultrasonic waves pressure amplitude per unit field strength ESA NV- m-i... 

The colloid vibration potential (difference) E or CVP is the a.c. potential difference measured between two Identical relaxed electrodes, placed in the dispersion if the latter Is subjected to an (ultra)sonlc field. CVP Is a particular case of the more general phenomenon, ultrasonic vibration potential (UVP), applying to any system, whether or not colloids are present. This field sets the particles into a vibrating motion, as a result of which the centres of particle charge and countercharge are periodically displaced with respect to each other. This phenomenon is the a.c. equivalent of that observed in the Dorn effect. Counterpart to this is the electrokinetic sonic amplitude, ESA, the amplitude of the (ultra)sonlc field created by an a.c, electric field in a dispersion. 

Electroktnetic sonic amplitude (ESA) Is the reverse process a high-frequency a.c. field is applied to the sol or dispersion, imposing an oscillatory motion on the particles which. In turn, generates a pressure wave with the same frequency, but not necessarily the same phase, as that of the applied field. The pressure wave can conveniently be detected with a plezo-electrlc transducer. The ESA Is the pressure amplitude per unit electric field, SI units m Pa = N V m L The phenomenon was discovered and patented by Oja et al. . For a paper with some review character see ). 

Sonnefeld, J., Lobbus, M., and Vogelsberger, W.. Determination of electric double layer parameters for spherical silica particles under application of the triple layer model using surface charge density data and results of electrokinetic sonic amplitude measurements, Colloids Surf. A, 195, 215, 2001. 

The kinetic potential is usually denoted as the zeta (0 potential and it is determined from the electrophoretic mobility of the extremely dilute particles in an electric field. More recently, the nse of electrokinetic sonic amplitude (ESA), acoustosizer (AZR), or colloid (or ultrasonic) vibration potential (CVP) has become available for the determination of the potential in rather concentrated particle suspensions. Again the potential may be measured as a function of either the metal concentration or the pH. In the latter case the point where the mobility ceases is denoted the isoelectric point (pH,Ep Fignre 8.27). It correlates particnlarly well with the stability of the sol. 

Because electrophoresis uses optical detection, this technique is limited to the analysis of dilute systems however, the recent development of electroacoustic methods has extended analysis to concentrated slurries containing up to 50% vol/vol solids [73], The electroacoustic effect is the response of charged particles to an applied alternating electrical or acoustical field [74], in contrast to the static field employed in electrophoresis. The acoustical response results from relative vibratory motion between particle and medium if the two phases differ in density. If an alternating electrical field is applied, charged particles vibrate in a back-and-forth motion in phase with the applied field, producing a sound wave whose pressure amplitude is proportional to the particle mobility and This technique is termed electrokinetic sonic amplitude (ESA). Alternatively, if an ultrasonic wave is applied, the particles vibrate at the sound... 

Electrokinetic sonic amplitude ESA, also termed electrosonic amplitude), an electro-acoustical method involving detection of the sound wave generated when dispersed species are made to move (oscillate) by an imposed alternating electric field (the principal features of the technique are shown in... 

Acoustics has a related field that is usually referred to as electroacoustics (8). Electroacoustics can provide particle size distribution as well as zeta potential. This relatively new technique is more complex than acoustics because an additional electric field is involved. As a result, both hardware and theory become more complicated. There are even two different versions of electroacoustics depending on what field is used as a driving force. Electrokinetic sonic amplitude (ESA) involves the generation of sound energy caused by the driving force of an applied electric field. Colloid vibration current (CVC) is the phenomenon where sound energy is applied to a system and a resultant eleetrie field or eurrent is created by the vibration of the colloid electric double layers. 

Electroacoustic phenomena. They are electrokinetic phenomena that have recently gained interest, both experimentally and theoretically. In the ESA (electrokinetic sonic amplitude) technique, an alternating electric field is applied to the suspension and the sound wave produced in the system is detected and analyzed. The colloid vibration potential (CVP) or colloid vibration current (CVI) is the reciprocal of the former a mechanical (ultrasonic) wave is forced to propagate through the system, and the resulting alternating potential difference (or current) is measured. 

Figure 5.17 Principle of acoustophorcsis. Concerning the UVP (Ultrasonic Vibration Potential - top), an ultrasonic wave applied on a liquid (transducer) induces solvent motion. As the two charged species have a different masses and frictional coefficients, its move differently. The charge heterogeneonsness which appeared in this way generate a macrr opic and thus measurable electric field (electrodes). Concerning the ESA (Electro Sonic Amplitude - bottom), an alternative electric field is applied (electrodes). Eachs ion species moves in opposite direction. This motion induces a detectable ultrasonic wave (transducer).

Different from acoustic attenuation spectroscopy, in electroacoustic spectral analysis, sound waves are generated by an applied high frequency electric field across a colloidal suspension and subsequently detected. This is called the electrokinetic sonic amplitude effect (ESA) [38]. These sound waves arise because the alternating electric field pushes the suspended particle forwards and backwards. By measuring the magnitude and phase angle of the sound waves at multiple frequencies (typically from 1-10 MHz), the particle dynamic mobility, Pd, can be determined, provided the concentration and the density of the... 

Similarly to LFDD, there is a set of electrokinetic techniques that involves ac fields and that can be applied to suspensions of arbitrary particle concentration, as they do not rely on optical techniques of evaluation. These are the so-called electroacoustic techniques, which enable the determination of the dynamic or ac mobility, u, of colloidal particles (the ac counterpart of the dc or classical electrophoretic mobility) as a function of frequency. There are basically two such techniques. One is based on the determination of the electric potential difference induced by the passage of a sound wave through the system it is called colloid vibration potential (CVP) or colloid vibration current (CVI), depending on the quantity measured. In the second technique, reciprocal of CVP or CVI, the basic process is the generation of a pressure wave when an ac electric field is applied to the suspension the amplitude of the sound wave, A sa is known as electrokinetic sonic amplitude, and so we speak of the ESA effect. After the very early works in the subject, O Brien [27,28] was the first author to perform a rigorous investigation on the physical foundations of electroacoustic techniques, and he found that Me is in fact proportional to [28] ... 

The Electrokinetic Sonic Amplitude (ESA) effect in this context refers to the generation of ultrasound by the application of an alternating electric field to a colloid. Previous reviews on the ESA have mainly focused on the determination of particle size and zeta potential from the ESA. While this is certainly a very important application of the ESA phenomenon, there is more information in the ESA spectmm than just particle size and zeta. It can be used, for instance, to determine the thickness of adsorbed polymer layers or the surface conductance under the shear plane. It is these other applications that will be our main interest here. To begin we will give an alternative explanation for the ESA phenomenon, one that allows a deeper understanding of the underlying physics. 

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