Polyelectrolyte assisted charge titration spectrometry: applications to latex and oxide nanoparticles

TL;DR

The paper introduces PACTS, a simple, cost-effective spectrometry method that measures particle charge density using minimal samples by analyzing light scattering peaks from polymer-particle assemblies.

Contribution

It presents PACTS as a novel technique for determining particle charge density, applicable to various nanoparticles, with optimized protocols for pH, concentration, and polymer molecular weight.

Findings

Successfully applied to latex and oxide nanoparticles

Requires minimal sample quantities

Broad applicability to charged nano-objects

Abstract

The electrostatic charge density of particles is of paramount importance for the control of the dispersion stability. Conventional methods use potentiometric, conductometric or turbidity titration but require large amount of samples. Here we report a simple and cost-effective method called polyelectrolyte assisted charge titration spectrometry or PACTS. The technique takes advantage of the propensity of oppositely charged polymers and particles to assemble upon mixing, leading to aggregation or phase separation. The mixed dispersions exhibit a maximum in light scattering as a function of the volumetric ratio X, and the peak position XMax is linked to the particle charge density according to {\sigma} ~ D0 XMax where D0 is the particle diameter. The PACTS is successfully applied to organic latex, aluminum and silicon oxide particles of positive or negative charge using poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). The protocol is also optimized with respect to important parameters such as pH and concentration, and to the polyelectrolyte molecular weight. The advantages of the PACTS technique are that it requires minute amounts of sample and that it is suitable to a broad variety of charged nano-objects.