Characterization of the Ultralow Interfacial Tension in Liquid–Liquid Phase Separated Polyelectrolyte Complex Coacervates by the Deformed Drop Retraction Method

Abstract

Dilute droplets form upon changing the temperature of a phase separated polyelectrolyte complex coacervate. This provides an in situ approach to measure the interfacial tension between supernatant (dilute droplet) and dense coacervate by the deformed drop retraction (DDR) method. The aqueous coacervate, formed via a model 1:1 by charge stoichiometric polyelectrolyte blend, exhibits ultralow interfacial tension with the coexisting phase. DDR finds the interfacial tension scales as γ = γ0(1 – C s/C s,c)μ, with μ = 1.5 ± 0.1, γ0 = 204 ± 36 μN/m, and C s,c = 1.977 mol/L. The value of μ independently validates the classical exponent of 3/2. The scaling holds between C s/C s,c of 0.75 to 0.94, the closest measurements to date near the critical salt concentration (C s,c). The temperature dependence of the interfacial tension is consistent with observed lower critical solution phase behavior and classical scaling. A detailed account of the DDR method and validation of assumptions are demonstrated.

Shape Recovery of Deformed Biomolecular Droplets: Dependence on Condensate Viscoelasticity

“…Equation (83a) is identical to the recovery rate widely quoted for droplets approximated as ellipsoids [29,30,32,34,37].…”

“…For some polymer blends, phase separation leads to polymer-poor "bubbles" forming in the coacervate matrix [37]. In this case, !…”

“…They noted the even higher viscosity of the nucleoplasm surrounding nucleoli, a type of biomolecular condensates specializing in ribosomal biogenesis, than that of droplets formed by a main nucleolar protein [17]. In addition, polymer blends may phase separate to produce dilute-phase "bubbles" in dense coacervates [37], also leading to !! / !…”

“…This problem has also been tackled by numerically solved the fluid-dynamics equations [31][32][33]. There have also been a number of experimental studies on the deformation retraction of polymer blends [34][35][36][37], often indicating the effects of viscoelasticity.…”

“…This problem has also been tackled by numerically solving the fluid-dynamics equations (Hooper et al, 2001; Mukherjee and Sarkar, 2010; Verhulst et al, 2009b). There have also been a number of experimental studies on the deformation retraction of polymer blends (Ali and Prabhu, 2019; Luciani et al, 1997; Tretheway and Leal, 2001; Verhulst et al, 2009a), often indicating the effects of viscoelasticity.…”