Confinement and Charge Induced Liquid–Liquid Phase Separation

Liquid–liquid phase separation (LLPS) is a spontaneous process that governs many cellular mechanisms and is implicated in the development of some biological disorders, including Alzheimer's disease and certain cancers. A recent experimental study in which peptide solutions are measured using atomic force microscopy (AFM) shows that LLPS could be induced under the AFM tip, when the solution is confined between the charged AFM tip and the substrate. To understand this experimental result, we develop a theory to model a polyelectrolyte solution under spatial confinement and applied electrostatic potential, and we use this model to investigate the phase separation mechanism. We show that both confinement and an applied electric field can induce liquid–liquid phase separation in polyelectrolyte solutions.