Zeta Potential of Membranes

Streaming potential was measured using a Brookhaven Instruments Corp. (Holtsville, NY, USA) BI-EKA commercial instrument which has a crossflow slit geometry. Childress and Elimelech (1996) and Elimelech et al. (1994) described the measuring cell and the principle in detail. For comparison, another surface potential analyser was used as constructed and described by Pihlajamaki (1998). The streaming potential, from which the zeta potential can be calculated with the Helmholtz-Smoluchowski equation, was measured in the presence of 10 mM NaCl, 1 mM NaHCO s and 0.5 mM CaCh, unless otherwise 

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Shimizu, Y., K. Yokosawa, K. Matsushita, I. Miura, T. Yazawa, H. Yanagisawa and K. Eguchi. 1989. Zeta potential of alumina membrane. Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi 97(4) 498-501. 

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. 

Several investigators measure the zeta potential of the membrane by measuring that of the membrane precursor particles or the particles obtained from grinding the membrane. 

Thus alumina membranes surface modified with silanes and sulfone [Shimizu et al. 1987] and with trimethyl chlorosilane TMS [Shimizu et al. 1989] and glass membranes adsorbed with surfactants [Busscher et al. 1987] have been studied this way. The results show that surface treatments alter the zeta potentials. Shimizu et al. [1989] have also demonstrated that under normal operating conditions the zeta potentials of alumina membranes do not change over time even for a period of two to three years. The isoelectric point for alumina particles thus determined is close to 4.00 as determined by direct measurement of membranes. 

Fig. 3. Visualization of the liposome morphology and size distribution determined with AFM and NanoZS. (a, b) Pure phospholipon liposomes adhered on silicon wafer as substrate. The liposomes have diameters between 80 and 250 nm with an average diameter of 178 12 nm. The liposomes tend to spread to the surface, because of the low membrane stability, (c) Pure GDNT liposomes with an average diameter of 137 8 nm (PDI 0.295 0.017) and a zeta potential of -15.3 0.60 mV. The liposomes are stable and show a spherically, round shape, (d) Size distribution of the pure GDNT liposomes measured with NanoZS...

Huisman, I.H. etal.. Determining the zeta-potential of ceramic microfiltration membranes using the electroviscous effect, J. Membr. Sci., 147, 187, 1998. 

Negatively charged membranes are also available. The fractionation capability of "tortuous-pore membrane" is enhanced considerably by using filters with a zeta potential of the same sign as the particles (usually negative). It should be noted that untreated nylon membranes have a negative zeta potential at pH values above 6.5 (see Figure 2.21 ).18... 

Figure 2.21 Zeta potential of positively charged and uncharged nylon membranes.

The zeta potential of both membranes in a clean state and of the pretreated GVHP membrane are illustrated as a function of pH in Figure 5.2. Electronmicrographs of the respective membrane surfaces are shown in Figure 5.3A and B. 

Figure 5.2 Zeta potential of dean membranes (a) GVHP, (b) GVWP, (c) GVHP pretreated with 50% ethanol solution.

These membrane filtration results are presumably again correlated with the different aggregation behaviour of the hematite colloids for different concentrations of fulvic acid. Indeed, as shown in Figure 6.27, the cake resistance is at a minimum at the fulvic acid concentration (approximately 1 mg.L ) where the zeta potential of the hematite particles is close to zero and where rapid aggregation has previously been observed to occur (Amal et al (1992)). At fulvic acid concentrations either side of this critical concentration, aggregation has been seen to be retarded due to the presence of high residual surface charge. 

Table 7.6 Zeta potential of the NF membranes in different salt solutions at pH 8.

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