Electrokinetic sound waves

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. 

By this term two phenomena are understood, both referring to the Interaction between sound waves and dispersions of charged particles. These methods somewhat transcend the borders set for this section in that the inertia of the particles does play a role in this respect electroacoustics anticipates a.c. electrokinetics and dielectric dispersion (sec. 4.8). 

When an alternating voltage is applied to a colloid, the particles move back and forth with a velocity that depends on their size and zeta potential and on the frequency of the applied field. As they move, the particles generate sound waves. This phenomenon is called the electroacoustic effect, which can be measured and what was named electrokinetic sonic amplitude (ESA) [5],... 

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... 

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. 

ElGCtrokinetiC Phenomena. Electrokinetic motion occurs when the mobile part of the electric double layer is sheared away from the inner layer (charged surface). There are several types of electrokinetic measurements, electrophoresis, electroosmosis, streaming potential, sedimentation potential, and two electroa-coustical methods. The first four methods are described in References 35 and 62. Of these the first finds the most use in industrial practice. The electroacoustical methods involve detection of the sound waves generated when dispersed species are made to move by an imposed alternating electric field, or vice versa (63). In all of the electrokinetic measurements either the liquid is made to move across a... 

Another method for the determination of electrophoretic mobility which has emerged in recent years is that of the measurement of the electrokinetic sonic amplitude (ESA) for a particle subjected to an alternating current (8). This electroacoustic effect is a result of the oscillation of the particles near the electrodes where a sound wave is produced that can be picked up by a pressure transducer located behind the electrode. The ESA pressure signal is simultaneously proportional to the dynamic mobility of the particle, the particle volume fraction and the density difference between particle and solvent. Thus, the electroacoustic effect is appropriate for concentrated dispersions where conventional electrophoretic methods are inappropriate. However, one disadvantage of the method is that it is not appropriate to systems having low density differences between the particles and suspending liquid. 

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] ... 

More recendy, Matec has introduced their AcoustoSizer, which measures electrokinetic sonic amplitude as a function of frequency (dififusion wave spectroscopy). Rather large samples (400 ml) are required in the concentradon range 1-40 vol%. The particle size range is 0.1-10 pm. The Pen Kem AcoustoPhor 8000 is based on the measuimient of attenuation of sound as it passes through the dispersion. It is claimed to have a range of 0.1 -10 pm plus, requires a sample volume of 1(K) ml and is applicable to dispersions greater than 40 voI%. 

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