Dynamics of the stratification process in drying colloidal dispersions studied by terahertz time-domain spectroscopy

TL;DR

This study uses terahertz time-domain spectroscopy to investigate the real-time stratification dynamics in drying colloidal dispersions, revealing how drying regimes influence layer formation.

Contribution

It introduces in situ terahertz spectroscopy for monitoring stratification in drying colloidal dispersions, distinguishing behaviors in evaporation versus diffusion controlled regimes.

Findings

Stratification occurs only in evaporation-controlled drying.

The dry top layer and wet bottom layer thicknesses vary dynamically during drying.

The coating remains a single layer in diffusion-controlled drying.

Abstract

We present an optical study that reveals the bulk dynamics of the stratification process in drying colloidal dispersions. Terahertz time-domain spectroscopy has been used to measure in situ solventborne and waterborne paint layers as a function of drying time. The dynamic behavior of the dry top layer and wet bottom layer thickness, as well as the bulk thickness, reflect the principal processes of the established drying mechanism. In addition, the results demonstrate stratification only when the drying process is in the evaporation controlled regime, whereas the coating is shown to remain a single layer for diffusion controlled drying.