Associative and Segregative Liquid-Liquid Phase Separation in Macromolecular Solutions

TL;DR

This paper analyzes two modes of liquid-liquid phase separation in macromolecular solutions, deriving analytical models and revealing distinct thermodynamic and interfacial properties that differentiate associative from segregative LLPS.

Contribution

The study introduces analytical expressions for critical points and binodal boundaries, and characterizes the thermodynamic and interfacial differences between ALLPS and SLLPS.

Findings

ALLPS involves polymers co-concentrating in one phase

SLLPS results in separate polymer phases

Interfacial tension is higher in ALLPS

Abstract

We investigate liquid-liquid phase separation (LLPS) and interfacial properties of two LLPS modes: associative (ALLPS) and segregative (SLLPS). Analytical expressions for the critical point (CP) and binodal boundaries are derived and show excellent agreement with self-consistent field (SCF) lattice computations. Distinct thermodynamic features differentiate ALLPS from SLLPS: (1) in ALLPS, polymers co-concentrate within a single dense phase coexisting with a solvent-rich phase, whereas in SLLPS each polymer forms a separate phase; (2) the attractive interaction per monomer in ALLPS is strongly dependent on solvent quality, but solvent-independent in SLLPS; and (3) ALLPS binodals exhibit near-universal behavior, largely independent of solvent content. SCF results further show that interfacial tension increases and interfacial width decreases with distance from the CP. We provide scaling relations for both quantities are provided. Compared with SLLPS, ALLPS displays higher interfacial tension and a thinner interface, reflecting distinct molecular organization at the liquid-liquid boundary.