Determination of zeta-potential of nanofluids based on electrolyte solutions from the measurements by the methods of electrical spectroscopy and laser correlation spectroscopy

TL;DR

This paper develops a theoretical model to determine the zeta-potential of electrolyte-based nanofluids using electrical conductivity measurements and laser correlation spectroscopy, enabling more accurate characterization of nanoparticle suspensions.

Contribution

The work introduces a rigorous model linking conductivity, zeta-potential, and stagnant layer properties, and proposes a method combining spectroscopy and conductivity measurements for zeta-potential determination.

Findings

The model predicts different conductivity behaviors based on stagnant layer parameters.

The zeta-potential can be inferred from the rate of change of conductivity with concentration.

Laser correlation spectroscopy provides the nanoparticle hydrodynamic radius necessary for calculations.

Abstract

The work discusses the problem of measurement of the zeta-potential for electrolyte-based suspensions of nanoparticle. A theory is presented for the effect of the diffuse electric double layer, including the interphase (stagnant) layer, on the effective conductivity of such suspensions. The theory is based on the method of compact groups of inhomogeneities applied to a model system of hard-core-penetrable-shell particles embedded together with the base liquid in a uniform host of the conductivity. The cores represent the particles. The shells are electrically inhomogeneous in the radial direction, their conductivity profile being a continuous function. This model is possible to analyze rigorously in the static limit. The desired conductivity is found from the integral relation which allows us to express the electrical conductivity in the terms of the zeta-potential, thickness of the stagnant layer, matrix molarity, etc. The theory reveals the existence of different scenarios of behavior of the conductivity depending on the geometrical and electrical parameters of the stagnant layer. It is shown that the functional dependence between the thickness and zeta-potential can be obtained from the rate of change of the conductivity with concentration for diluted suspensions; this rate can be measured experimentally. It is pointed out that the hydrodynamic radius of a nanoparticle can be obtained from the Smoluchowski-Einstein diffusion coefficient, which can be measured by the method of laser correlation spectroscopy. In order to find the zeta-potential, it is necessary to simultaneously do a series of independent measurements: find the slope of the conductivity and estimate the thickness of the stagnant layer.