Droplet Microfluidics for the Label‐Free Extraction of Complete Phase Diagrams and Kinetics of Liquid–Liquid Phase Separation in Finite Volumes

Abstract

Liquid–liquid phase separation of polymer and protein solutions is central in many areas of biology and material sciences. Here, an experimental and theoretical framework is provided to investigate the thermodynamics and kinetics of liquid–liquid phase separation in volumes comparable to cells. The strategy leverages droplet microfluidics to accurately measure the volume of the dense phase generated by liquid–liquid phase separation of solutions confined in micro‐sized compartments. It is shown that the measurement of the volume fraction of the dense phase at different temperatures allows the evaluation of the binodal lines that determine the coexistence region of the two phases in the temperature‐concentration phase diagram. By applying a thermodynamic model of phase separation in finite volumes, it is further shown that the platform can predict and validate kinetic barriers associated with the formation of a dense droplet in a parent dilute phase, therefore connecting thermodynamics and kinetics of liquid–liquid phase separation.

Long term phase separation dynamics in liquid crystal-enriched microdroplets obtained from binary fluid mixtures

“…Our approach may have ramifications beyond liquid crystals in a generalised context of confinement-induced changes in phase stability, 52 which ranges from small molecules ( e.g. , ethanol–water mixtures 53–57 ) to biomolecular solutions 58–60 and polymer blends, 61 and also in crystallization of proteins in droplets. 62,63…”

“…Crucially, further lowering of the system temperature re-introduced an isotropic-to-nematic transition of the droplets, reinforcing the explanation that methanol uptake is responsible for the nematic-to-isotropic droplet phase transition. Our approach may have ramifications beyond liquid crystals in a generalised context of confinement-induced changes in phase stability, 52 which ranges from small molecules (e.g., ethanol-water mixtures [53][54][55][56][57] ) to biomolecular solutions [58][59][60] and polymer blends, 61 and also in crystallization of proteins in droplets. 62,63 4 Experimental section…”

Long term phase separation dynamics in liquid crystal-enriched microdroplets obtained from binary fluid mixtures

“…Crucially, further lowering of the system temperature re-introduced an isotropic-to-nematic transition of the droplets, reinforcing the explanation that methanol uptake is responsible for the nematic-to-isotropic droplet phase transition. Our approach may have ramifications beyond liquid crystals in a generalised context of confinement-induced changes in phase stability, 50 which ranges from small molecules (e.g., ethanolwater mixtures [51][52][53][54][55] ) to biomolecular solutions [56][57][58] and polymer blends, 59 and also in crystallization of proteins in droplets. 60,61…”

Nucleation of Biomolecular Condensates from Finite-Sized Simulations

“…This is particularly relevant in the context of biological systems, where phase separations take place in micrometerscale isolated cellular compartments, as well as in the rational development of technological applications of LLPS for material synthesis in micro/nanofluidic devices. 37,38 Acknowledgement MS and LL acknowledge the Leverhulme Trust for funding (Project RPG-2019-235), MS and ARF acknowledge funding from the EPSRC Programme Grant Crystallization in the Real World (Grant EP/R018820/1). The authors acknowledge the use of the UCL High-Performance Computing Facilities and associated support services in the completion of this work.…”

“…This is particularly relevant in the context of biological systems, where phase separations take place in micrometer-scale isolated cellular compartments, as well as in the rational development of technological applications of LLPS for material synthesis in micro/nanofluidic devices. 40,43…”