Theory of capillary-induced self-coacervation in zwitterionic polymer solutions

Journal of Chemical Physics. 2026. Vol. 164. No. 15. Article 154904.

Nikolai N. Kalikin, Petr E. Brandyshev, Yury A. Budkov

This study presents a mean-field theory for zwitterionic polymer solutions confined within attractive slit-like nanopores. Building upon our prior model for self-coacervation [Budkov et al., Soft Matter 19, 3281–3289 (2023)], we demonstrate that strong electrostatic dipole–dipole correlations between monomeric units, coupled with attraction to pore walls, can induce capillary-driven liquid–liquid phase separation inside the pore—a phenomenon we term capillary-induced self-coacervation. Using a thermomechanical approach (Budkov et al., J. Stat. Mech.: Theory Exp. 2024, 123201), we calculate the disjoining pressure, revealing a pronounced non-monotonic dependence on pore width linked to coacervate film formation and rupture. Remarkably, we identify a crossover between two film formation mechanisms controlled by wall attraction strength. For weak adsorption, film formation is bridging-dominated, with critical pore width scaling as Hc ∼ N^1/2 . For strong adsorption, the system crosses over to a cohesion-dominated regime where Hc saturates to an N-independent plateau, indicating collective phase behavior governed by a confinement-induced shift of the local binodal. This duality reveals the interplay between singlechain connectivity and collective thermodynamics in confined polyzwitterions. The theory offers new insights into coacervate film formation on mineral surfaces, with implications for prebiotic compartmentalization.

Keywords: Disjoining pressure, Расклинивающее давление, coacervation, Коацервация, zwitterions, capillary condensation, цвиттерионы, растворы полимеров, капиллярная конденсация