Critical surface phase behavior governs hydrophobic attraction between extended solutes

Abstract

Hydrophobic interactions are central to biological self-assembly and soft matter organization, yet their microscopic origins remain debated. A key hallmark is the strengthening of attraction between hydrophobic solutes with increasing temperature, a feature often attributed to entropy changes from disrupted hydrogen bonding in water. Here we present an alternative framework based on surface phase behavior, supported by extensive molecular dynamics simulations. Using metadynamics, we quantify the solvent-mediated effective potential between nanometer-scale hydrophobic solutes in the monatomic water (mW) model, the Simple Point Charge Extended water model, and a Lennard-Jones solvent. We develop a morphometric model which incorporates a scaling theory of critical drying, linking the range and strength of hydrophobic attraction to interfacial thermodynamics and proximity to vapor–liquid coexistence. The model reproduces the effective potential across diverse solute sizes, degrees of hydrophobicity, and thermodynamic states. Our simulations recover the inverse temperature dependence of hydrophobicity, showing it arises generically from rapid thermal expansion of the solvation shell.