On the Quantification of Mixing in Microfluidics

TL;DR

This paper reviews various mixing indices in microfluidics, experimentally verifies the most representative one, and advocates for the relative mixing index due to its robustness against lighting variations.

Contribution

It identifies the relative mixing index as the most reliable measure for quantifying mixing in microfluidic experiments, considering lighting conditions.

Findings

Relative mixing index is unaffected by lighting conditions.

Other mixing indices are sensitive to lighting variations.

The study recommends using the relative mixing index for microfluidic mixing quantification.

Abstract

Methods for quantifying mixing in microfluidics have varied largely in the past, and various indices have been employed to represent the extent of mixing. Mixing between two or more colored liquids is usually quantified using simple mathematical functions operated over a sequence of images. The function, usually termed mixing indices, involves a measure of standard deviation. Here, we first review some mixing indices and then experimentally verify the index most representative of a mixing event. It is observed that the relative mixing index is not affected by the lighting conditions, unlike other known mixing indices. Based on this finding, the use of a relative mixing index is advocated for further use in the lab-on-a-chip community for quantifying mixing events.