Liquid–liquid phase separation and self-assembly of hexanoic acid and ethyl hexanoate in ethanol–water systems: a model for aged colloidal Baijiu

Abstract

Liquid–liquid phase separation (LLPS) in the pre-Ouzo region governs the early-stage aggregation of amphiphiles, dictating the non-equilibrium evolution of soft materials. However, classical turbidimetry, which defines phase boundaries by macroscopic cloudiness, is blind to this metastable regime. Here, we introduce an integrated fluorescence–microscopy ternary phase mapping approach that directly probes the pre-Ouzo region in a canonical ethanol–water–amphiphile system. This method reveals critical aggregation concentrations that are 2–3 orders of magnitude below the binodal—a regime inaccessible to turbidimetry. Applying this diagram to naturally aged Baijiu (1–20 years), a dynamically evolving colloidal system, uncovers a pronounced aging-enhanced solubilization: the dissolution ratios of key amphiphiles (hexanoic acid and ethyl hexanoate) exceed 96%, with dissolved concentrations far surpassing static equilibrium predictions. Mechanistic investigations show that this phenomenon arises from the synergistic restructuring of ethanol–water hydrogen-bond networks and the expansion of hydrophobic microdomains. Our work not only provides a high-resolution tool for mapping non-equilibrium phase behavior but also establishes a direct link between slow microstructural evolution and the emergence of kinetically stabilized, supersaturated states in complex fluids.