Molecular Rotors for In Situ Viscosity Mapping during Evaporation of Confined Fluid Mixtures

Abstract

Numerous formulation processes of materials involve a drying step, during which evaporation of a solvent from a multicomponent liquid mixture, often confined in a thin film or in a droplet, leads to concentration and assembly of nonvolatile compounds. While the basic phenomena ruling evaporation dynamics are known, precise modeling of practical situations is hindered by the lack of tools for local and time-resolved mapping of concentration fields in such confined systems. In this article, the use of fluorescence lifetime imaging microscopy and of fluorescent molecular rotors is introduced as a versatile, in situ, and quantitative method to map viscosity and concentration fields in confined, evaporating liquids. More precisely, the cases of drying of a suspended liquid film and of a sessile droplet of mixtures of fructose and water are investigated. Measured viscosity and concentration fields allow characterization of drying dynamics, in agreement with simple modeling of the evaporation process.

Fast Recombination of Free Radicals in Solution and Microviscosity

“…The use of fluorescence lifetime imaging microscopy and fluorescent molecular rotors is suggested as a versatile quantitative method to map η micro . Measured microviscosity and concentration fields allow the characterization of drying time dependence in agreement with simple modeling of the evaporation [31].…”

“…The processing of initially liquid materials often involves a drying step, during which a solvent evaporates from a multicomponent mixture. Such materials are usually confined in a thin film or a droplet [31]. Examples of such materials may be paints or coatings.…”

“…The observed η of the material measured one or another way cannot reflect the occurring changes in different parts of the drying material. The authors of [31] found a way to measure microviscosity for local and time-dependent mapping of concentration fields in such confined systems. The use of fluorescence lifetime imaging microscopy and fluorescent molecular rotors is suggested as a versatile quantitative method to map η micro .…”