Characterizing properties of polymers and colloids by their reaction-diffusion behavior in microfluidic channels

Abstract

Molecular mobility is a key factor that determines the behavior of supramolecular systems in various applications such as drug delivery. Characterizing transport properties of such systems may be a labor-intensive process requiring a set of different experimental techniques. In this work, we performed a theoretical analysis of factors that govern the phase behavior of colloid systems in microfluidic channels and discussed the specific features of confined phase separation. Theoretical considerations allowed to propose a simple approach to analyzing diffusion characteristics of polymers and colloids by performing their microfluidic reactions with oppositely charged counterparts and characterizing diffusivities of the reaction species by the locations of emerging ordered precipitate lines. Positions of these lines allow to detect conformational changes of polyelectrolytes, micellization in surfactant solutions, and aggregation of polymer- surfactant complexes, and also evaluate diffusion coefficients of the reagents without additional macroscopic techniques. A set of Matlab scripts represents the mathematical model behind this approach. These scripts calculate optimal microchip operation parameters and evaluate diffusion coefficients from microfluidic experiments, which agree well with the results of applicable macroscopic methods. Microfluidic analysis of reacting flows can serve as a simple, fast, and cost-effective additional or alternative approach to characterize diffusivities, conformation changes, and aggregation of colloid and polymer systems. • Oppositely charged reacting colloidal systems generate lines of precipitates in microflows. • Positions of precipitates are governed by diffusion coefficients of the reagents. • Precipitation behavior allows to detect micellization or aggregation in reactive solutions. • Diffusion coefficients of colloidal particles can be evaluated in reactive microflows. • The analysis requires only an optical microscope with a flow focusing chip.