Zeta potential probe

An interesting practical application of electroacoustic phenomena is the recent development of a so-called zeta potential probe, which, essentially, is the electroacoustic... 

A.S. Dukhin, P.J. Goetz, S. Truesdail, Titration of concentrated dispersions using electroacoustic zeta-potential probe. Langmuir 17(4), 964-968 (2001). doi 10.1021Aa001024m J.A. Enderby, On electrical effects due to sound waves in colloidal suspensions. Proc. Roy. Soc. 

However, the equilibrium of the indicator adsorbed at an interface may also be affected by a lower dielectric constant as compared to bulk water. Therefore, it is better to use instead pH, the interfacial and bulk pK values in Eq. (50). The concept of the use at pH indicators for the evaluation of Ajy is also basis of other methods, like spin-labeled EPR, optical and electrochemical probes [19,70]. The results of the determination of the Aj by means of these methods may be loaded with an error of up to 50mV [19]. For some the potentials determined by these methods, Ajy values are in a good agreement with the electrokinetic (zeta) potentials found using microelectrophoresis [73]. It is proof that, for small systems, there is lack of methods for finding the complete value of A>. 

Initially, this mechanism was proposed on the basis of results obtained for zeta potential and flotation (Fig. 29). The formation of the hydrophobic aggregates at the interface was confirmed after the advent of the fluorescence probing technique. The adsorption isotherm is determined in the presence of pyrene as the fluorescent probe and the emission spectra of pyrene in both supernatant and slurries were analyzed after adsorption. The h/h of pyrene in solutions of SDS containing 0.1 M NaCl and in the slurry are shown in Figs. 30 and 31. In solution, the ratio remains at around 0.6 till the CMC (as determined by surface tension measurement) is attained. Above CMC, the value becomes 1.0 due to the solubilization of pyrene in micelles. In... 

Figure 1. (Bottom) Diagram of the electrostatic potential adjacent to a membrane bearing a positive charge. The zeta potential is the potential at the hydrodynamic plane of shear, which should be about 2 A from the surface of the membrane. (Top) Schematic of the location of the probe molecules used to detect the potential produced by the adsorption of calcium and other alkaline earth cations to membranes formed from PC. The divalent cation cobalt and the amphipathic, anionic, fluorescent probe TNS will sense the potential at the interface. The non-actin-Rf complex will sense the potential in the center of the membrane.

Size exclusion/molecular sieve chromatography Ultra Itration/dia lysis Ultracentrifugation Fluorescent probes Spin label EPR NMR probes Calorimetry Microelectrophoresis Zeta potential... 

The work of Larson et al. (62) represented the first detailed study to show agreement between AFM-derived diffuse layer potentials and ((-potentials obtained from traditional electrokinetic techniques. The AFM experimental data was satisfactorily fitted to the theory of McCormack et al. (46). The fitting parameters used, silica and alumina zeta-potentials, were independently determined for the same surfaces used in the AFM study using electrophoretic and streaming-potential measurements, respectively. This same system was later used by another research group (63). Hartley and coworkers 63 also compared dissimilar surface interactions with electrokinetic measurements, namely between a silica probe interacting with a polylysine coated mica flat (see Section III.B.). It is also possible to conduct measurements between a colloid probe and a metal or semiconductor surface whose electrochemical properties are controlled by the experimenter 164-66). In Ref. 64 Raiteri et al. studied the interactions between... 

Figure 9.30. (a) Adsorption isotherm of sodium dodecyl sulfate (SDS) on alumina at pH 6.5 in 0.1 M NaCl. (b) Zeta potential of alumina as a function of equilibrium concentration of SDS (designation of regions based on isotherm shape). (From Chandar et al., 1987 based on the data of Somasundaran and Fuerstenau, 1966.) Chandar et al. (1987) have shown with the aid of fluorescent probe studies that in region II and above adsorption occurs through the formation of surfactant aggregates of limited size. 

Chemical probing of powder Probe fluid qO Parti ate phase Inverse gas chromatography Preferential adsorption with probe gases Electrokinetics Zeta potential and charge Surfactant adsorption Preferential adsorption with probe surfactants References Lloyd et al. (eds.), ACS Symposium Series 391, ACS, Washington, 1989. Aveyard and Haydon, An Introduction to the Principles of Surface Chemistry, Cambridge University Press, 1973. Shaw, Introduction to Colloid and Surface Chemistry, Butterworths Co. Ltd., 1983. 

Understanding of the structure of the adsorbed surfactant and polymer layers at a molecular level is helpful for improving various interfacial processes by manipulating the adsorbed layers for optimum configurational characteristics. Until recently, methods of surface characterization were limited to the measurement of macroscopic properties like adsorption density, zeta-potential and wettability. Such studies, while being helpful to provide an insight into the mechanisms, could not yield any direct information on the nanoscopic characteristics of the adsorbed species. Recently, a number of spectroscopic techniques such as fluorescence, electron spin resonance, infrared and Raman have been successfully applied to probe the microstructure of the adsorbed layers of surfactants and polymers at mineral-solution interfaces. 

Electrokinetic potential of the alumina samples redispersed in 0.001 N KNO3 was measured over a pH range between 2 and 9.5 with a Pen Chem System 300 instrument. The coated alumina powder was ultrasonically dispersed at 0.001 wt% into 300 mL of 0.001 N KNO3 for ca. 15 min and immediately placed under N2 atmosphere. A 50-mL portion was placed onto a titration stirrer under N2 atmosphere that was fitted with a pH probe, a mechanical stirrer, and a port for addition of titrant. A portion of sample was pumped into the S3000 cell, which was fitted into a constant temperature bath set at 25 °C. This sample portion was used to rinse the cell of the previous sample. A second portion of sample was pumped into the cell. The pH was recorded and the zeta potential was measured. Two measurements were taken, one at the front stationary layer and the second at the back stationary layer. The histograms were then combined and averaged. The pH was adjusted with either 0.01 N KOH or 0.01 N HNO3, and measurements were repeated for each desired pH value. Once all the desired pH versus zeta potential data were obtained, the data were transferred to an IBM PC and plotted. Estimates of isoelectric points (IEPs) were made from the plots obtained. 

ICP analyses were performed by Plasma Absorption Emission Spectroscopy (ICP-AES). BET surface areas were measured with a Micromeritics TriStar 3000 instrument after degassing the samples at 150 C under a 0.13 Pa vacuum overnight. XPS analyses were performed on a SSI X-probe spectrometer (SSX-100/206 photoelectron spectrometer Fisons) equipped with a monochromatized microfocused Al Ka X-ray source (1486.6 eV) and a hemispherical analyser. The binding energies were calculated relative to the C-(C, H) component of the adventitious Cls carbon peak fixed at 284.8 eV. Zeta potential measurements were carried out in a PENKEM Zeta Meter 500, using 25 mg of sample ultrasonically dispersed in 200 ml of an aqueous solution... 

Electrokinetic phenomena arise when the mobile layer of the EDL interacts with an externally applied electric field resulting in relative motion between the solid and liquid phases. There are three types of electrokinetic phenomena relevant to microfluidics electroosmotic flow, streaming potential, and electrophoresis. In aU of these cases, the zeta potential is a key parameter that defines either the fluid flow or particle motion. Since it is not possible to probe the zeta potential directly, measurements are based on indirect readings obtained from electrokinetic experiments. The following discussion focuses on modem methods of measuring the zeta potential using electroosmotic flow, electrophoresis, and streaming potential. 

Some of the experimental techniques employed in these studies have included determining the change in surfactant concentration in the bulk solution npon adsorption, zeta potential measurements, and probe tecbniqnes (electron spin resonance and fluorescence). Attempts to describe the adsorption behavior exhibited in tbe adsorption isotherms has led to the development of several mathematical models [26, 30-33]. To date, none of the models are capable of fully accounting for all of the phenomena which affect surfactant adsorption without introducing ad hoc assnmptions and adjustable parameters, but they bave offered some interesttug insights. 

Important measurands for the characterisation of the EDL are the surface charge density and the electrokinetic potential or zeta-potential. The zeta-potential is the electric potential at a h3q)othetical shear plane, which separates the mobile solvent from solvent molecules that adhere to the particle surface. The zeta-potential can he probed by imposing a relative motion between bulk solvent and particle (Delgado et al. 2007). 

Fig. 1 Charge inversion for polyelectrolyte multilayers represented as the surface potential dependence on the number of adsorbed layer, N. a Charge inversion as it was obtained by the Kelvin probe for (PDADMAC + PSS) multilayers adsorbed from a NaCl solution of concentration 50 mM onto a flat surface. Adapted from Ref. [80] with permission from The Royal Society of Chemistry, b Zeta potential of (PSS + PAH)n multilayers deposited onto colloidal microparticles of methylformamide with a positive bare charge. Adapted with permission from Ref. [52]. Copyright (1998) American Chemical Society, c Zeta potential changes evaluated using Streaming potential for multilayers built with PSS and PAH, the results are represented as zeta potential against number of measurement. The number of measurements is related to the number of times that each single layer was measured and it shows as accumulative number with the increase of the layer number. Adapted with permission from Ref. [83]. Copyright (2000) American Chemical Society...

Zhang, Y., Yang, M., Portney, N. G., Cui, D., Budak, G., Ozbay, E., Ozkan, M., and Ozkan, C. S. (2008J. Zeta potential A surface electrical characteristic to probe the interaction of nanoparticles with normal and cancer human breast epithelial cells. Biomed Microdevices, 10, 321-328. 

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