Salting-In and Salting-Out of Water-Soluble Polymers in Aqueous Salt Solutions

Abstract

To obtain further experimental evidence for the mechanisms of the salting effect produced by the addition of salting-out or sating-in inducing electrolytes to aqueous solutions of water-soluble polymers, systematic studies on the vapor-liquid equilibria and liquid-liquid equilibria of aqueous solutions of several polymers are performed in the presence of a large series of electrolytes. Polymers are polyethylene glycol 400 (PEG400), polyethylene glycol dimethyl ether 250 (PEGDME250), polyethylene glycol dimethyl ether 2000 (PEGDME2000), and polypropylene glycol 400 (PPG400), and the investigated electrolytes are KCl, NH(4)Cl, MgCl(2), (CH(3))(4)NCl, NaCl, NaNO(3), Na(2)CO(3), Na(2)SO(4), and Na(3)Cit (tri-sodium citrate). Aqueous solutions of PPG400 form aqueous two-phase systems with all the investigated salts; however, other investigated polymers form aqueous two-phase systems only with Na(2)CO(3), Na(2)SO(4), and Na(3)Cit. A relation was found between the salting-out or sating-in effects of electrolyte on the polymer aqueous solutions and the slopes of the constant water activity lines of ternary polymer-salt aqueous solutions, so that, in the case of the salting-out effect, the constant water activity lines had a concave slope, but in the case of the salting-in effects, the constant water activity lines had a convex slope. The effect of temperature, anion of electrolyte, cation of electrolyte, and type and molar mass of polymers were studied and the results interpreted in terms of the solute-water and solute-solute interactions. The salting-out effect results from the formation of ion (specially anion)-water hydration complexes, which, in turn, decreases hydration, and hence, the solubility of the polymer and the salting-in effect results from a direct binding of the cations to the ether oxygens of the polymers.

Phase separation in aqueous solutions of polypropylene glycol and sodium citrate: Effects of temperature and pH

“…Other poly (alkylene glycol)s such as PPGs as close relatives of PEGs, sharing several of their benign properties may also been taking into account as phase polymer in ABS for green separations. However, liquid-liquid equilibrium (LLE) data of the aqueous PPG-polymer and PPG-salt systems are relatively scarce [11][12][13][14][15][16].…”

Aggregational Attitude of Hexadecyltrimethylammonium Bromide in Aqueous Solutions of Sodium Salt at 298.15k

“…This also led to easier formation of micelles (lowering of the CMC value). Anions with higher valency hydrated more water molecule and therefore they are more effective than anions with lower valency to promote the surfactant to go to micellar phase (pseudo phase) similar to the one observed in the case of aqueous two-phase system formulation [32,33]. …”

Volumetric and compressibility behaviour of poly(propylene glycol) – Amino acid aqueous solutions at different temperatures

“…In aqueous solutions of solute 1-solute 2, which can form ABS, the solute1-water interactions become more stable in the presence of solute 2. In other words, solute 1 and solute 2 exclude themselves from the vicinity of each other due to the their preferential hydration [4,[26][27][28]. Accordingly, the interaction of PPG with water in aqueous amino acid solutions is stronger than that in pure water.…”