A novel particle tracking method with individual particle size measurement and its application to ordering in glassy hard sphere colloids

TL;DR

This paper introduces a new particle tracking method capable of accurately localizing and measuring individual particle sizes in 2D and 3D images, enabling detailed analysis of local order and crystallization in colloidal suspensions.

Contribution

The novel method allows simultaneous particle localization and size measurement in crowded environments, revealing size-dependent ordering phenomena in colloids.

Findings

Crystal-like order forms where small particles are depleted.

Small particles are expelled from growing crystals.

Size-dependent local ordering influences crystallization behavior.

Abstract

Particle tracking is a key to single-particle-level confocal microscopy observation of colloidal suspensions, emulsions, and granular matter. The conventional tracking method has not been able to provide accurate information on the size of individual particle. Here we propose a novel method to localise spherical particles of arbitrary relative sizes from either 2D or 3D (confocal) images either in dilute or crowded environment. Moreover this method allows us to estimate the size of each particle reliably. We use this method to analyse local bond orientational ordering in a supercooled polydisperse colloidal suspension as well as the heterogeneous crystallisation induced by a substrate. For the former, we reveal non-trivial couplings of crystal-like bond orientational order and local icosahedral order with the spatial distribution of particle sizes: Crystal-like order tends to form in regions where very small particles are depleted and the slightly smaller size of the central particle stabilizes icosahedral order. For the latter, on the other hand, we found that very small particles are expelled from crystals and accumulated on the growth front of crystals. We emphasize that such information has not been accessible by conventional tracking methods.