On measuring colloidal volume fractions

TL;DR

This paper critically reviews how volume fractions in colloidal suspensions are measured, highlighting that systematic errors of 3-6% are common and significantly impact experimental comparisons with theories and simulations.

Contribution

It provides a detailed analysis of uncertainties in measuring colloidal volume fractions and discusses their implications for experimental results and theoretical comparisons.

Findings

Statistical uncertainties can be as low as 0.0001 in relative phi values.

Systematic errors of 3-6% are likely unavoidable in measurements.

Systematic errors significantly affect comparisons of experimental data with theories.

Abstract

Hard-sphere colloids are popular as models for testing fundamental theories in condensed matter and statistical physics, from crystal nucleation to the glass transition. A single parameter, the volume fraction (phi), characterizes an ideal, monodisperse hard-sphere suspension. In comparing experiments with theories and simulation, researchers to date have paid little attention to likely uncertainties in experimentally-quoted phi values. We critically review the experimental measurement of phi in hard-sphere colloids, and show that while statistical uncertainties in comparing relative values of phi can be as low as 0.0001, systematic errors of 3-6% are probably unavoidable. The consequences of this are illustrated by way of a case study comparing literature data sets on hard-sphere viscosity and diffusion.