Experimental Determination of Configurational Entropy in a Two-Dimensional Liquid under Random Pinning

TL;DR

This study introduces a new experimental method to analyze how random immobilization of particles affects the entropy and mobility in a two-dimensional colloidal liquid, revealing a smooth transition from fluid-like to arrested states.

Contribution

A novel experimental approach for random pinning in colloidal systems and the first direct measurement of local entropic fluctuations related to particle immobilization.

Findings

Increasing pinning concentration arrests the system gradually.

Transition from high mobility/high entropy to low mobility/low entropy.

Local entropic fluctuations correlate with particle mobility.

Abstract

A quasi two-dimensional colloidal suspension is studied under the influence of immobilisation (pinning) of a random fraction of its particles. We introduce a novel experimental method to perform random pinning and, with the support of numerical simulation, we find that increasing the pinning concentration smoothly arrests the system, with a cross-over from a regime of high mobility and high entropy to a regime of low mobility and low entropy. At the local level, we study fluctuations in area fraction and concentration of pins and map them to entropic structural signatures and local mobility, obtaining a measure for the local entropic fluctuations of the experimental system.