Water/Cosolvent Attraction Induced Phase Separation: A Molecular Picture of Cononsolvency

Abstract

Cononsolvency is a phenomenon for which the solubility of a macromolecule decreases or even vanishes in the mixture of two good solvents. Although it has been widely applied in physicochemical, green chemical and pharmaceutical industry, its origin is still under active debate. Here, by using combined neutron total scattering, deuterium-labelling and all-atom molecular dynamic simulations, we demonstrated that it is the strong water/cosolvent attraction that leads to the cononsolvency. The combined approach presented here has opened a new route for investigating the most probable allatom structure in macromolecular solutions and the thermodynamic origin of solubilities.The solubility of macromolecules is of fundamental importance in many scientific disciplines and industrial applications. Unfortunately, the existing theoretical framework to describe the solvation of macromolecules are constructed primarily based on empirical observations without knowing the real solubility parameters, which cannot be measured directly 1, 2 . One problematic consequence of this inability to directly measure the real macromolecular solubility parameter, is that several important dissolution phenomena cannot then explained in the existing framework of understanding; cononsolvency is a typical example 3 .Since the first evidence of cononsolvency was found in the 1980s, theoretical debates on its origin have continued. Currently, there are four main hypotheses, i.e., the perturbation of the water-cosolvent interaction with the presence of polymer network 4 , Competitive adsorption 5, 6 , the formation of a stoichiometric complexation between water and cosolvent 7 , and strong water-cosolvent interactions 8 . Although still widely considered, we note that the first hypothesis was tarnished when Schild et al. 9 found that similar cononsolvency phenomena happened in both macromolecular dilute solution and

The effect of saccharides on equilibrium swelling of thermo-responsive gels

“…Keeping in mind that the hydration number characterizes interaction between molecules of water and molecules of an additive, the proportionality between the coefficient K and hydration number n means that the parameter c 12 in eqn (31) (that accounts for this interaction in the Flory-Rehner model) plays the key role in the volume phase transition of TR gels. This conclusion is in accord with the concept of complexation of cosolvent molecules, [43][44][45] according to which hydration of polymer chains requires formation of cage-like structures of water molecules surrounding hydrophobic segments. When water…”

“…As a result, the "naked" segments aggregate into hydrophobic clusters, the polymer chains dehydrate, and the network collapses. [43][44][45] The novelty of our study consists in the following: (i) a model is developed for the mechanical response and equilibrium swelling of TR gels in aqueous solutions of additives. Unlike the conventional approach, we do not introduce phenomenological dependencies of the FH parameters c ij on volume fractions of polymer chains or cosolvent molecules.…”

Rapid and scalable fabrication of ultra‐stretchable, anti‐freezing conductive gels by cononsolvency effect

“…Therefore, it is highly desirable to develop new strategies for producing conductive anti‐freezing gels remaining mechanically robust under low temperatures. We propose that this critical demand can be addressed by fabricating gel via the cononsolvency effect, the phenomenon of solubility decrease of a macromolecule in the mixture of two good solvents 27‐30 . This phenomenon has been widely applied in the physicochemical, green chemical, and pharmaceutical industries 27,31 .…”

“…We propose that this critical demand can be addressed by fabricating gel via the cononsolvency effect, the phenomenon of solubility decrease of a macromolecule in the mixture of two good solvents 27‐30 . This phenomenon has been widely applied in the physicochemical, green chemical, and pharmaceutical industries 27,31 . Poly(vinyl alcohol) (PVA) can form a hydrogel in a mixture of water and dimethyl sulfoxide (DMSO) via the cononsolvency effect, attributed to the strong interaction between water and DMSO molecules 28,32‐35 .…”

Neutron total scattering investigation on the dissolution mechanism of trehalose in NaOH/urea aqueous solution

“…A cosolvent can influence the solubility of a solute via direct or indirect interaction. In the former case, the cosolvent binds to the solute molecule directly; 25 while in the latter case, it interacts with the solvent (water in this case) to form a new static or dynamic structure, 26 which changes the solubility of the solute. Pure liquid water has a short-range ordered tetrahedral structure, without any long-range order.…”