Microfluidic device coupled with total internal reflection microscopy for in situ observation of precipitation

TL;DR

This paper introduces a microfluidic device combined with total internal reflection microscopy for high-resolution, in situ observation of phase separation and precipitation processes, overcoming scattering issues in traditional methods.

Contribution

The study presents a novel quasi-2D microfluidic device with TIR microscopy for real-time observation of precipitation, enabling controlled mixing and high-resolution imaging.

Findings

Effective diffusion-driven mixing confirmed by fluorescence microscopy

Controlled composition of mixtures achieved by tuning solution B

Successful in situ observation of asphaltene precipitation and beta-alanine crystallization

Abstract

In situ observation of precipitation or phase separation induced by solvent addition is important in studying its dynamics. Combined with optical and fluorescence microscopy, microfluidic devices have been leveraged in studying the phase separation in various materials including biominerals, nanoparticles, and inorganic crystals. However, strong scattering from the subphases in the mixture is problematic for in situ study of phase separation with high temporal and spatial resolution. In this work, we present a quasi-2D microfluidic device combined with total internal reflection microscopy as an approach for in situ observation of phase separation. The quasi-2D microfluidic device comprises of a shallow main channel and a deep side channel. Mixing between a solution in the main channel (solution A) and another solution (solution B) in the side channel is predominantly driven by diffusion due to high fluid resistance from the shallow height of the main channel, which is confirmed using fluorescence microscopy. Moreover, relying on diffusive mixing, we can control the composition of the mixture in the main channel by tuning the composition of solution B. We demonstrate the application of our method for in situ observation of asphaltene precipitation and beta-alanine crystallization.