# Temporal Evolution of Interparticle Potentials of PMMA Colloids in CHB/Decalin

## TL;DR

This study investigates how the interactions between PMMA colloids in a solvent mixture change over time and how adding TBAB affects these interactions.

## Contribution

The study reveals that particle interactions evolve over time due to charging effects and that TBAB significantly reduces electrostatic forces.

## Key findings

- Variations in particle properties are caused by temporal evolution of particle charging.
- Adding small amounts of TBAB drastically reduces electrostatic forces between colloidal particles.
- Contact potentials remain even at high TBAB concentrations.

## Abstract

Colloidal dispersions composed of polymethylmetacrylate
particles
dispersed in a mixture of cyclohexyl bromide and decalin find widespread
use as model systems in optical microscopy experiments. While the
system allows simultaneous density and refractive index matching,
preparing particles with hard potentials remains challenging, and
strong variations in the physical parameters of samples prepared in
the same manner are commonly observed. Here, we present data on the
measurement of forces between individual pairs of particles in highly
diluted dispersions over the course of tens of days using the blinking
optical tweezers method. Our results show that the variations in the
particle properties are indeed caused by a temporal evolution of the
particles’ charging. Additional measurements of the influence
of the addition of tetrabutylammonium bromide (TBAB) to the dispersions
show that already small concentrations of added TBAB salt drastically
decrease the electrostatic forces between colloidal particles. However,
small, non-negligible contact potentials remain even at the highest
TBAB concentrations added.