Electroacoustic Methods

The first four methods are described in Refs. [81,253,254] and the electroacoustical methods in [130,255-257]. Of these, electrophoresis finds the most use in industrial practice. The electroacoustic methods are perhaps the best suited to studying concentrated suspensions and emulsions without dilution [258], In all of the electro-kinetic measurements, either liquid is made to move across a solid surface or vice versa. Thus the results can only be interpreted in terms of charge density (a) or potential (zeta potential, ) at the plane of shear. The location of the shear plane is generally not exactly known and is usually taken to be approximately equal to the potential at the Stern plane, = W d), see Figure 4.9. Several methods can be used to calculate zeta potentials [16,81,253], Some of these will be discussed here, in the context of electrophoresis results. 

A.J. Babchin, R.S. Chow and R.P. Sawatzky, Electrokinetic Measurements by electroacoustical methods. Adv. Colloid Interface Sci. 30 (1989) 111. (Review, theory and applications.)... 

Electroacoustic method, 80 Electrokinetic potential effect on interaction energy between colloidal particles, 248 effect of ionic strength on, 66 of macroscopic samples, 79 of oxides, effect of hydration time on, 76 relationship to thd. 649, 656 in solution of weak electrolyte, 242 at very high ionic strengths, 266, 267 Electronegativity, correlation with PZC, 213... 

The pHo obtained by means of electrokinetic measurements is reported as iep in the Method columns in the tables in Chapter 3. The trade names of commercial instruments or short descriptions of home-made instruments used for electrokinetic measurements are given when possible. The present approach is different from that in [2], in which the type of instrument was not specified. Moreover, the present book does not consider pHg values obtained by means of an electroacoustic method as a separate category, and they are also reported as iep. ... 

The tables in Chapter 3 report results obtained by means of the following commercial instruments based on the electroacoustic method ... 

Increasing the ionic strength from 0.01 to 0.1 M had a rather insignificant effect on the positive potentials of alumina and zirconia determined in [509] by the electroacoustic method. The absolute value of the negative potential was clearly depressed as the ionic strength increased, according to expectations. 

Reference [31] reports an extensive study by electrophoresis and an electroacoustic method at pH 7-10. The particles were negatively charged, but when sufficient amounts of Co(ii) and then NaOH were added, an IEP at pH 9.8 was observed, probably owing to formation of hydroxide. 

In principle, metal surfaces are outside the scope of the present book. An electrophoretic study of water on silver has been published [1906]. The contact angle of silver film was studied as a function of pH [693], and the maximum was identified with the IEP. Copper was studied by means of electrophoresis [1802]. The streaming potential of Au and Al is reported in [294]. Nickel was studied by means of electrophoresis [122], and by means of electroacoustic method in [2721]. An adhesion method was used to estimate the lEPs of eight metals [689] and of Cu [2720],... 

A shift in the lEPs of the following metal oxides to high pH was induced by concentrated solutions of Li and Na salts alumina [492] (electroacoustic method and electrophoresis), [494,1018] (only Li induced a shift in the IEP Na did not), ceria [1224], hematite [430], India and niobia [1674], rutile [430], anatase [495] (multi-instrument, multilaboratory study), [1985], [1986] (the shift in the IEP was accompanied by a shift in the maximum of viscosity), [1987,1988], and zirconia... 

Beattie, J.K. and Djerdjev, A., Rapid electroacoustic method for monitoring dispersion Zeta potential titration of alumina with ammonium poly(methacrylate), J. Am. Ceram. Soc., 83, 2360, 2000. 

Kosmuiski, M., Studies on electrokinetic potential by the electroacoustic method, Przemysl Chem., 87, 381, 2008. 

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... 

Various experimental methods for monitoring the kinetics of coagulation in emulsions have been developed, such as the electroacoustic method (167), direet video-enhaneed microscopic investigation (168), and ultrasonie attenuation spectroscopy (169). 

An electroacoustic method based on the application of a sonic field and detection of the electric signal proved to be a reliable technique for measuring the kinetics of coagulation/coalesence process of colloidal systems in non-polar and non-transparent media like water-in-crude oil emulsion. 

Use of the electroacoustic method (O Brien et al., 1995) to determine both potential and particle size is both new and holds considerable promise. 

Static and dynamic scattering techniques are spectroscopic characterisation methods in the sense of Sect. 2.2. These techniques evaluate the functional dependency of measurement signals on a spectral parameter, i.e. on time, space, or classically on wavelength or frequency. The major advantage of spectroscopic methods is the reduced sample preparation (no fractionation), but they involve the inversion problem. That is, the spectrum is a—most frequently incomplete and discrete— nonlinear projection of the size distribution. Beside the scattering techniques, there are further spectroscopic methods which are based on the extinction of radiation or on any other response of the particle system to an external field. This section describes optical, acoustic, and electroacoustic methods that have gained relevance for the characterisation of colloidal suspensions. 

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... 

Ensminger, D., 1988. Acoustic and electroacoustic methods of dewatering and drying. Drying Technol. 6(3) 473-499. 

Instead of temperature fields, one can use pressure discontinuities in order to probe charge or polarization distributions in dielectrics. According to the pressure excitation method, one can distinguish three basic configurations (a) the LIPP (laser-induced pressure pulse. Fig. 21) (Sessler et al. 1981) or PWP (pressure wave propagation) technique (Alquie et al. 1981), (b) the piezoelectrically generated pressure step technique (PPS, cf. Fig. 22) (Eisenmenger and Haardt 1982), and (c) the pulsed electroacoustic method (PEA, cf Fig. 23) (Takada et al. 1987). 

Chen G, Xu Z, Zhang L (2007) Measurement of the surface potential decay of corona-charged polymer films using the pulsed electroacoustic method. Meas Sci Technol 18 1453-1458... 

---