Zeta potential measurement, aqueous system

The knowledge of the surface potential for the dispersed systems, such as metal oxide-aqueous electrolyte solution, is based on the model calculations or approximations derived from zeta potential measurements. The direct measurement of this potential with application of field-effect transistor (MOSFET) was proposed by Schenk [108]. These measurements showed that potential is changing far less, then the potential calculated from the Nernst equation with changes of the pH by unit. On the other hand, the pHpzc value obtained for this system, happened to be unexpectedly high for Si02. These experiments ought to be treated cautiously, as the flat structure of the transistor surface differs much from the structure of the surface of dispersed particle. The next problem may be caused by possible contaminants and the surface property changes made by their presence. 

The problem of temporal and thermal instability of the U-P[3F-C 12-( 11)] modifier was solved by utilizing a —CF2CF2H (4F) fluorous side chain and increasing the Cl2 mole fraction. Biocidal effectiveness was demonstrated after storage for at least a month under ambient conditions of temperature and humidity. This stability was correlated with zeta potential measurements of accessible near surface charge. These results suggest zeta potential measurements hold promise as a physical method for assessing effectiveness of polycation contact kill and polycation stability in contact with aqueous systems. 

Electrostatics in Non-Aqueous Media. A popular misconception in studies of non-aqueous dispersions concerns electrostatic effects. Because these are more difficult to measure than in aqueous media, there has been a general tendency to ignore them completely. However, the few investigators who have measured zeta-potentials or electrodeposition with these systems have become convinced of their importance. With the advent of modern commercial instrumentation for zeta-potentials in non-aqueous media it is to hoped that these effects will be measured rather than ignored. 

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 ESA-8000 can make accurate estimates of zeta potential in both aqueous and nonaqueous environments, but it has a number of limitations. Since it measures at only one frequency, it cannot determine both the size and the charge. It is also unsuitable for handling concentrated systems sinee it has no provision for estimating the acoustic impedance of the suspension which is required to obtain from Eq. (1). Determining the acoustic impedance is relatively easy, but estimating the phase angles with the necessary precision (about 1°) is quite difficult. Both those problems were ad-... 

With the electrostatic approach, ions or charged molecules are attracted to or dissociated from the particle surfaces to produce a system of similarly charged particles. When the repulsive double-lsiyer electrostatic forces between the particles are greater than the attractive Van der Waals forces, the particles repel to produce a dispersed system. The net Interparticle force (In aqueous solutions) can be altered by changing the type of concentration of the ionic species as well as the pH. When the particle charge approaches zero, the particles floe and eventually produce a very open network of touching particles. The zeta potential provides a convenient experimental measure of such forces. 

In the Appendix a survey is made of the literature on laboratory electrophoretic deposition systems involving non-aqueous media, including ceramic, glass, metallic and mixed powders. The list is unlikely to be exhaustive. Patents are not listed but can be found from the papers referred to. Furthermore, there are numerous examples of suspensions that have been described but which do not exhibit useful deposition characteristics these have not been included. No attempt has been made here to identify the role of the additives, which may according to circumstances function as dispersants, deflocculants, electrolytes or binders. Experimental parameters such as zeta potential are often not reported, but in some cases electrophoretic mobility or coulombic yield have been measured or can be estimated from the data. Fuller details will be found in the references. 

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