Colloid vibration potential

UltrasonicVibration Potential (UVP), an electroacoustica] method involving detection of the alternating electric field (potential or current) generated when dispersed species are made to move by imposed sound waves (Figure 4.8). This technique is also referred to as colloid vibration potential (CVP), or colloid vibration current (CVC). 

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. 

This equation is the basis of both the electrovibration sind vibration potential listed in the electrokinetic phenomena of Table 9.10. In these cases, the root mean square (rms) voltage i=E L) is either measured as in the case of the colloid vibration potential or induced by an electrode and the rms pressure fluctuations (= AP) at the same fi quency are either induced by an ultrasonic actuator or measured with a pressure transducer, as in the case of electrovibration. 

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]. 

Colloid Vibration Potential in a Suspension of Soft Particles... 

FIGURE 26.2 Colloid vibration potential caused by the asymmetry of the electrical double layer around the particles. 

COLLOID VIBRATION POTENTIAL IN A SUSPENSION OF SOFT PARTICLES... 

Colloid vibration potential ultrasonic field particles liquid alternating electric field electric field amplitude per unit velocity of ultrasonic field vlbr CVP V s m ... 

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. 

The first phenomenon Is the colloid vibration potential CVP or already... 

Pen Kem System 7000 Acoustopheretic Titrator Pendse and co-workers used discrete frequencies in the development of the Acoustophoretic titrator. This instrument is based on the measurement of colloidal vibration potential arising from the motion of suspended solids relative to the suspending medium when subjected to a sound field, was the first commercial instrument capable of monitoring zeta potential of concentrated solids. 

Colloid vibration potentials offer a means of measuring the zeta-potential, and hence charge, on colloid particles. Values of-KT4 Vein s at frequencies of a few hundred kilohertz seem to be typical of this effect, and a range of colloids were examined, including silver, silver iodide, and arsenic trisulfide. 

Pressure gradient Filtration Particle oscillations Streaming current and potential Colloid vibration potential... 

Fig. V-29. Schematic representation of dynamic polarization of the electrical double layer in the field of acoustic wave, leading to the appearance of colloid vibration potential (CVP) [35]...

In acoustic spectroscopy sound is utilized as both the excitation and the measured variable, and therefore there is but one basic implementation. In contrast, electroacoustic spectroscopy deals with the interaction of electric and acoustic fields and therefore there are two possible implementations. One can apply a sound field and measure the resultant electric field which is referred to as the colloid vibration potential (CVP), or conversely one can apply an electric field and measure the resultant acoustic field which is referred to as the ESA. 

First, let us consider the measurement of CVR When the density of the particles Pp differs from that of the medium Pjjj, the particles move relative to the medium under the influence of an acoustic wave. This motion causes a displacement of the internal and external parts of the double layer (DL). The phenomenon is usually referred to as a polarization of the DL (6). This displacement of opposite charges gives rise to a dipole moment. The superposition of the electric fields of these induced dipole moments over the collection of particles gives rise to a macroscopical electric field which is referred to as the colloid vibration potential (CVP). Thus, the fourth mechanism of particles interaction with sound leads to the transformation of part of the acoustic energy to electrical energy. This electrical energy may then be dissipated if die opportunity for electric current flow exists. 

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. 

The existence of the colloidal vibration potential (CVP) was predicted in the 1930s (Debye 1933 Hermans 1938a, b Rutgers 1938) and intensively investigated— both experimentally and theoretically after the Second World War (Rutgers 1946 Enderby... 

Fig. 2.22 Generation of the colloid vibration potential (CVP) or current (CVI) in ultrasonic fields...

An unusual approach to studying the charge on silica particles was employed by Deraska, Yaeger, and Hovorka (201). A Ludox colloidal silica having a particle diameter of 15 nni was subjected to ultrasonic vibration by placing electrodes at nodes and loops they measured the colloidal vibration potential which increased with silica concentration from zero to about 4% silica. The potential is presumably generated by the motion of the charged particles with respect to the fixed electrode. 

Ohshima H et al.(2006) Colloid Vibration Potential in a Suspension of Spherical Colloidal Particles. Colloids and Surfaces B Biointerfaces 56 16-18. 

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