Zeta potential AcoustoSizer

The original Acoustosizer used a single frequency whereas a later development has a range of 13 frequencies between 0.3 and 13 MHz. This allows the measurement of the dynamic mobility spectrum and the determination of the zeta potential and particle size. In order to invert the mobility spectrum into a size distribution a log-normal distribution of particle size is assumed. A comparison with photon correlation spectroscopy for determining particle size and laser Doppler anemometry for particle charge eonfirmed the results using ACS [266]. These and additional sedimentation measurements confirmed that changes in particle size and zeta potential due to dilution effects are likely to occur in aqueous and non-stabilized systems. 

The commercial systems for zeta-potential determination using these electro-acoustic effects are typified by the AcoustoSizer 8000 (Matek Applied Sciences) consisting of five main components (Fig. 5). The synthesizer produces a continuous sinusoidal voltage which feeds into the gated amplifier. This creates a sinusoidal voltage pulse across the cell which contains the dispersion. The resulting ESA sound waves are... 

The AcoustoSizer software assumes that the size follows a lognormal distribution and adjusts the median and spread of the distribution, along with the zeta potential, to give the best fit to the mobility spectrum, by minimizing the relative root mean square error (superscript th is the theoretical) ... 

This instrument factor A is determined by calibration. This involves the measurement of the signal from a material that has a known ESA. In the AcoustoSizer II an electrolyte is used for this calibration. The reason for using an electrolyte, rather than a colloid, is that colloids are notoriously variable in their zeta potential over time, whereas the ESA signal from the electrolyte is reproducible and can be calculated from its thermodynamic and transport properties [5j. 

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. 

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