Concentration Dependence of the Interfacial Tension for Aqueous Two-Phase Polymer Solutions of Dextran and Polyethylene Glycol

Abstract

We studied the interfacial tension between coexisting phases of aqueous solutions of dextran and polyethylene glycol. First, we characterized the phase diagram of the system and located the binodal. Second, the tie lines between the coexisting phases were determined using a method that only requires measuring the density of the coexisting phases. The interfacial tension was then measured by a spinning drop tensiometer over a broad range of polymer concentrations close to and above the critical point. In this range, the interfacial tension increases by 4 orders of magnitude with increasing polymer concentration. The scaling exponents of the interfacial tension, the correlation length, and order parameters were evaluated and showed a crossover behavior depending on the distance to the critical concentration. The scaling exponent of the interfacial tension attains the value 1.50 ± 0.01 further away from the critical point, in good agreement with mean field theory, but the increased value 1.67 ± 0.10 closer to this point, which disagrees with the Ising value 1.26. We discuss possible reasons for this discrepancy. The composition and density differences between the two coexisting phases, which may be taken as two possible order parameters, showed the expected crossover from mean field behavior to Ising model behavior as the critical point is approached. The crossover behavior of aqueous two-phase polymer solutions with increasing concentration is similar to that of polymer solutions undergoing phase separation induced by lowering the temperature.

Hydrodynamic interactions of deformable polymeric nanocarriers and the effect of crosslinking

“…The initial microstructure is a unit star polymer with 25 arms attached to a core, with each arm modeled by beads connected through four links in series; that is, each link connecting two adjacent beads in an arm is modeled as a Kuhn spring. Following the reports of Liu et al , 29 and Pelton et al , 30 the stiffness of each link and the equilibrium distance are determined using a freely jointed chain model.…”

“…If the number of Kuhn’s segments per bead is N k and the size of each Kuhn’s segment is b k , we impose N k b k = Nb , where b is the size of each monomer. For dextran, b k is 0.44 nm 29 and the size of the monomer ( b ) is 1.5 nm using which we calculate the stiffness ( k s ) of the links between beads as derived from the FJC model, i.e., $k_{\mathrm{s}}=\frac{3k_{\mathrm{B}}T}{N_{\mathrm{k}}{b_{\mathrm{normalk}}}^2}$. We also model the stiffness of the coarse-grained crosslinks to be identical to the stiffness of each link.…”

Bioreactor droplets from liposome-stabilized all-aqueous emulsions

“…24). Although ATPS have low interfacial tensions relative to oil/water systems 12,25 , cells, liposomes and microparticles have been observed at the aqueous/aqueous interface of bulk ATPS [26][27][28][29][30][31][32][33][34][35] . Recently, formation of water-in-water phase systems stabilized by latex beads 27 , fat globules 28 or protein particles have been reported 29 .…”

Surfactant Driven Post-Deposition Spreading of Aerosols on Complex Aqueous Subphases. 1: High Deposition Flux Representative of Aerosol Delivery to Large Airways

“…(23,24) As shown in Figure 1, these altered surface tensions can result in a lens that covers an area larger than that of a surfactant-free drop. In the cases examined here, where the drop and subphase are miscible, the effective surface tension at the drop/ subphase interface is very small, (25,26) such that the final area covered by the spread surfactant-laden drop is increased relative to the surfactant-free drop if the initial drop/vapor surface tension is smaller than the initial surface tension of the subphase. During the spreading process, surfactant escape from the drop and adsorption to the expanding drop/ subphase and drop/vapor interfaces continually deplete the surfactant concentration in the drop until a new interfacial tension balance among subphase/vapor, drop/vapor, and drop/subphase interfaces is achieved, ultimately limiting the final extent of spreading.…”