Microfluidic osmotic compression of a charge-stabilized colloidal dispersion: Equation of state and collective diffusion coefficient

TL;DR

This paper introduces a microfluidic method to rapidly measure the equation of state and collective diffusion coefficient of charge-stabilized colloidal dispersions, overcoming diffusion-related measurement limitations.

Contribution

It presents a microfluidic chip enabling quick EOS measurement at nanoliter scale and provides a new approach to estimate the collective diffusion coefficient from relaxation dynamics.

Findings

Microfluidic chip allows EOS measurement in hours.

Diffusion limits measurement times of the EOS.

Time-resolved analysis yields the collective diffusion coefficient.

Abstract

We show, using a model coupling mass transport and liquid theory calculations for a charge-stabilized colloidal dispersion, that diffusion significantly limits measurement times of its Equation Of State (EOS), osmotic pressure vs composition, using the osmotic compression technique. Following this result, we present a microfluidic chip allowing one to measure the entire EOS of a charged dispersion at the nanoliter scale in a few hours. We also show that time-resolved analyses of relaxation to equilibrium in this microfluidic experiment lead to direct estimates of the collective diffusion coefficient of the dispersion in Donnan equilibrium with a salt reservoir.