Measuring every particle's size from three-dimensional imaging experiments

TL;DR

This paper introduces a new microscopy-based method to accurately measure individual particle sizes in colloidal suspensions, enabling detailed analysis of polydispersity effects on structure and dynamics.

Contribution

The authors develop and validate a general technique for estimating particle radii from confocal microscopy, applicable to various colloidal systems and revealing new insights into their behavior.

Findings

Recovered full particle size distributions in situ

Improved structural analysis by accounting for particle size

Identified crystal nucleation in monodisperse regions

Abstract

Often experimentalists study colloidal suspensions that are nominally monodisperse. In reality these samples have a polydispersity of 4-10%. At the level of an individual particle, the consequences of this polydispersity are unknown as it is difficult to measure an individual particle size from microscopy. We propose a general method to estimate individual particle radii within a moderately concentrated colloidal suspension observed with confocal microscopy. We confirm the validity of our method by numerical simulations of four major systems: random close packing, colloidal gels, nominally monodisperse dense samples, and nominally binary dense samples. We then apply our method to experimental data, and demonstrate the utility of this method with results from four case studies. In the first, we demonstrate that we can recover the full particle size distribution {\it in situ}. In the second, we show that accounting for particle size leads to more accurate structural information in a random close packed sample. In the third, we show that crystal nucleation occurs in locally monodisperse regions. In the fourth, we show that particle mobility in a dense sample is correlated to the local volume fraction.