The determination of very small electrophoretic mobilities in polar and nonpolar colloidal dispersions using phase analysis light scattering

Miller, John F.; Schätzel, Klaus; Vincent, Brian

doi:10.1016/0021-9797(91)90286-h

Cited by 171 publications

(122 citation statements)

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“…The zeta potential in turn can be related to the electrical charge carried by the particle. The approach has been implemented in various forms on free particles in a DC electric field 4,15,16 or using an alternating field in combination with the particle-position control implemented optically 2,17 or piezoelectrically. 18 Fast detection and long observation times have further enabled the measurement of temporal fluctuations in electrical charge on very weakly charged optically trapped particles in a nonpolar solvent.…”

Section: Introductionmentioning

confidence: 99%

Measured electrical charge of SiO2 in polar and nonpolar media

Kokot

Bespalova

Krishnan

2016

The Journal of Chemical Physics

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We present measurements of the net electrical surface charge of silicon dioxide (SiO2) in contact with solvents of dielectric constants between 5 and 80. Our experimental approach relies on observing the thermal motion of single silica particles confined in an electrostatic fluidic trap created by SiO2 surfaces. We compare the experimentally measured functional form of the trapping potential with that from free energy calculations and thereby determine the net surface charge in the system. Our findings clearly demonstrate that contrary to popular perception, even in the absence of surfactants, the net electrical charge of ionizable surfaces in contact with apolar solvents can be large enough to lead to significant repulsive forces. A charge regulation model for SiO2 surfaces with a single tunable parameter explains our measurements. This model may find general applicability in estimating the net charge of ionizable surfaces, given system parameters such as the dissociation or association constants of the ionizable groups and the pH, ionic strength, and dielectric constant of the solvent phase. We present measurements of the net electrical surface charge of silicon dioxide (SiO 2 ) in contact with solvents of dielectric constants between 5 and 80. Our experimental approach relies on observing the thermal motion of single silica particles confined in an electrostatic fluidic trap created by SiO 2 surfaces. We compare the experimentally measured functional form of the trapping potential with that from free energy calculations and thereby determine the net surface charge in the system. Our findings clearly demonstrate that contrary to popular perception, even in the absence of surfactants, the net electrical charge of ionizable surfaces in contact with apolar solvents can be large enough to lead to significant repulsive forces. A charge regulation model for SiO 2 surfaces with a single tunable parameter explains our measurements. This model may find general applicability in estimating the net charge of ionizable surfaces, given system parameters such as the dissociation or association constants of the ionizable groups and the pH, ionic strength, and dielectric constant of the solvent phase. Published by AIP Publishing. [http://dx

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Section: Introductionmentioning

confidence: 99%

Measured electrical charge of SiO2 in polar and nonpolar media

Kokot

Bespalova

Krishnan

2016

The Journal of Chemical Physics

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“…Our home-built Laser Doppler Velocimetry (LDV) instrument combines the reference beam integral measurement of [34] (allowing to measure the complete flow-profile in a single measurement) with super-heterodyning [35,36,37] (allowing to separate the heterodyne part of the power spectrum from the homodyne part, electronic and low frequency noise) and a significant restriction of the detection volume [15,16] (to reduce detection of MS photons by approaching confocal detection conditions). The present machine is a modification of a previously described setup [19] now also allowing a continuous variation of the scattering angle.…”

Section: Integral Low-angle Super-heterodyne Ldvmentioning

confidence: 99%

An empirical correction for moderate multiple scattering in super-heterodyne light scattering

Botin

Mapa

Schweinfurth

et al. 2017

The Journal of Chemical Physics

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Frequency domain super-heterodyne laser light scattering is utilized in a low angle integral measurement configuration to determine flow and diffusion in charged sphere suspensions showing moderate to strong multiple scattering. We introduce an empirical correction to subtract the multiple scattering background and isolate the singly scattered light. We demonstrate the excellent feasibility of this simple approach for turbid suspensions of transmittance T 0.4. We study the particle concentration dependence of the electro-kinetic mobility in low salt aqueous suspension over an extended concentration regime and observe a maximum at intermediate concentrations.We further use our scheme for measurements of the self-diffusion coefficients in the fluid samples in the absence or presence of shear, as well as in polycrystalline samples during crystallization and coarsening. We discuss the scope and limits of our approach as well as possible future applications. PACS: if neededCorresponding author: Denis Botin dbotin@uni-mainz.de 2 INTRODUCTIONMultiple scattering (MS) strongly affects studies of turbid colloidal suspensions using Laser light scattering. Depending on the degree of MS, several different sophisticated approaches have been taken to use, correct for, or suppress MS in studies on suspension dynamics. At very large turbidities and small optical path lengths, suspension dynamics can be determined using diffusive wave spectroscopy (DWS) [1[2]]. In the regime of low to moderate multiple scattering, index matching is regularly employed [3, 4, 5], but it is not easily applicable in water based systems. Further, optical path lengths may be shortened by utilizing fibre optics [6]. In addition, cross correlation schemes [7] were pioneered by Phillies in the early eighties [8] and further developed to two-color or 2D cross correlation schemes [9, 10]. This way the methods and theory developed for (single) dynamic light scattering in the time domain [11] could be used also in turbid samples. Alternatively, in frequency domain, special mode selective heterodyne instrumentation was developed and applied to Brilluoin scattering [12,13,14]. Both cross correlation and mode selection, however, afford complex instrumentation and data evaluation schemes. A much simpler instrumentation is needed for the statistical analysis of heterodyne speckle fields taken at different times providing information about the velocity field in the fluid in a given plane perpendicular to the optical axis [15]. This information can be extracted, either by measuring their cross-correlation function or by recovering the power spectrum corresponding to the difference between the two speckle fields. Multiple scattering in this approach is minimized by using confocal geometry [16]. Yet another simple approach is path length resolved low coherence interferometry, which also is a static heterodyne technique [17,18]. There a certain small path length can be selected which corresponds to a single back-scattering event. Then only singly scattered light i...

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“…Measurements of particle size and surface charge are routinely performed using light scattering techniques such as phase analysis light scattering (PALS). [6] This technique estimates the size and electrophoretic mobility (EPM) of particles by measuring Doppler shift of laser light scattered by the particles due to their average Brownian motion and their motion in an applied electric field, respectively. While applicable to a wide variety of colloidal systems, PALS reports size and EPM values which represent averages over multiple particles.…”

Section: Physical Characterization Of Colloidsmentioning

confidence: 99%

Method for Single-Cell Mass and Electrophoretic Mobility Measurement

Dextras¹

2010

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The determination of very small electrophoretic mobilities in polar and nonpolar colloidal dispersions using phase analysis light scattering

Cited by 171 publications

References 4 publications

Measured electrical charge of SiO2 in polar and nonpolar media

Measured electrical charge of SiO2 in polar and nonpolar media

An empirical correction for moderate multiple scattering in super-heterodyne light scattering

Method for Single-Cell Mass and Electrophoretic Mobility Measurement

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