Zeta potential control

The practical significance of zeta-potential measurement lies in the fact that strong empirical correlation exists between the measured zeta potential of the system and the properties of the system which are the manifestation of the electrostatic interfacial phenomenon. Since the measurement of zeta potential can be conveniently performed, it becomes an ideal parameter for use in routine testing. Zeta-potential control has been successfully applied to various technical fields involving colloidal and non-colloidal systems. 

Andalaft, E., Vega, R., Correa, M., Araya, R. and Loyola, R 1997. Zeta potential control in decontamination with inorganic membranes and inorganic adsorbents. In Treatment Technologies for Low and Intermediate Level Waste from Nuclear Applications. Final Report of a Coordinated Research Programme 1991-1996. IAEA-TECDOC-929, pp. 15-32. IAEA Vienna. 

Stable colloids are achieved if the Debye length (double layer thickness) is very high (i.e. low salt content, low valency ions), if the colloid particles are in a medium with high relative permittivity, if they have low (or even negative) Hamaker constants and high values of the surface or zeta potential. Control of the ionic concentration and surface charge are crucial. 

In the following, we briefly describe two examples which support our arguments for two completely different apphcations and materials. First, we discuss the influence of the zeta-potential of alumina suspensions which were studied in the context of nanomiUing in stirred media mills. The zeta-potential is a measure of the surface charge of the particles and is here used to tailor the suspension rheology. Figure 13 shows that the magnitude of the zeta-potential controls the measured shear stress at low shear rates where the influence of interparticulate interactions can be monitored. 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

Zeta potentials of floe produeed in the plant may also be measured as a means of eontrol. The zeta potential value for optimum eoagulation must be determined for a given wastewater by aetual correlation with jar tests or with plant performance. The control point is generally in the range of 0 to 10 millivolts. If good correlations can be obtained between some zeta potential values and optimum plant performance, then it is possible to make rapid measurements of particle charge to compensate for major variations in wastewater composition due to storm flows or other causes. 

Flocculating agents can be simple electrolytes that are capable of reducing the zeta potential of suspended charged particles. Examples include small concentrations (0.01-1%) of monovalent ions (e.g., sodium chloride, potassium chloride) and di- or trivalent ions (e.g., calcium salts, alums, sulfates, citrates or phosphates) [80-83], These salts are often used jointly in the formulations as pH buffers and flocculating agents. Controlled flocculation of suspensions can also be achieved by the addition of polymeric colloids or alteration of the pH of the preparation. 

One of the most difficult parenteral dosage forms to formulate is a suspension. It requires a delicate balance of variables to formulate a product that is easily resuspended and can be ejected through an 18-to 21-gauge needle through its shelf life. To achieve these properties it is necessary to select and carefully maintain particle size distribution, zeta potential, and rheological properties, as well as the manufacturing steps that control wettability and surface tension. The requirements for, limitations in, and differences between the design of injectable suspensions and other suspensions have been previously summarized [17b, 18,19]. 

The zeta potential and the thickness of the double layer (1/k) decrease rapidly with an increase in ionic strength or the valence of the electrolytes in the capillary (Equations (5) and (6)). Therefore, the ionic strength and the nature of the ions in the electrolyte solution are very important parameters determining the strength of the EOF. Careful control of the ionic... 

Wang, L.K. Process Control Using Zeta Potential and Colloid Titration Techniques, PB87-179099/ AS US Department of Commerce, National Technical Information Service Springfield, VA, 1984,... 

In various kinds of industrial production, materials need to be treated with charged colloidal particles. In such systems, the value of the zeta-potential analyses are needed to control production. For example, in paper, adhesive, and synthetic plastics, colloidal clay can be used as filler. In oil drilling, clay colloidal suspensions are used. The zeta potential is controlled so as to avoid clogging the pumping process in the oil well. It has been found that, for instance, the viscosity of a clay suspension shows a minimum when the zeta potential is changed (with the help of pH from 1 to 7) from 15 to 35 mV. Similar observations have been reported in coal slurry viscosity. The viscosity was controlled by the zeta potential. 

Kamo et al. [Biochim. Biophys. Acta, 367, 1 and 11 (1974)] have shown that nonionic sugars modify the zeta potential of slime mold cells. Aggregation of colloids is related to their surface charge and their surface potential. This fact shows evidence of long-range electrostatic interactions controlled by metabolic reactions taking place at the membrane and able to modify the composition of the membrane medium interface. In this process the diffusion is not relevant, as indicated by Mrs. Babloyantz. 

Fig. 25 Characterization and luciferase expression of PGP DNA condensates in vivo. These results show that luciferase expression is dependent on galactose incorporation but independent of amount of melittin. (a) Represents the input mol ratio of Cys-terminated melittin, PEG-peptide, and glycopeptide. (b) Represents the measured mol ratio of Cys-terminated melittin, PEG-peptide, and glycopeptide for each purified PGP. (c) Values are the calculated MW based on polylysine standards, (d) Values are the calculated MW based on PEG standards, (e) The mean particle size determined at a stoichiometry of 0.3 nmol of PGP per mg of DNA. The value represents the mean diameter (nm) based on unimodal analysis, (f) The zeta potential of PGP DNA condensates at a stoichiometry of 0.3 nmol of PGP per mg of DNA. (g) The metabolic half-life of PGP 125I-DNA in triplicate mice. The results are derived from Fig. 6. (h) The PC/NPC ratio of DNA-targeted liver, (i) Represents a control PGP 3 in which galactose has been removed. Figure adapted with permission from [182], 2007 American Chemical Society...

Impact of control potential, EOF field and frequency for the zeta potential variation... 

Hunter, R.J. Coll. Surf. A, 2001, 395, 205-214. Riddick, T.M. Control of Stability Through Zeta Potential, Zeta Meter Inc. New York, 1968. Okada, K. Akagi, Y. J. Chem. Eng. Japan 1987, 20,11-15. 

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