Electrokinetic pressure wave

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] ... 

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

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... 

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. 

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