Cononsolvency is a phenomenon where two

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

s that can typically readily dissolve a

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

, when mixed, at certain ratios of these two solvents, are no longer able to dissolve the polymer. This phenomenon is in contrast to cosolvency where two solvents that are both poor at dissolving a material, but when the two poor solvents admixed, can form a mixed solvent capable of dissolving the material. The first works of both experimental and theoretical about the cononsolvency effect were published in the late 1970s. Since then, numerous studies focused on a manifold of different polymers that featured the cononsolvency effect in water and various organic

cosolvent In chemistry, cosolvents are substances added to a primary solvent in small amounts to increase the solubility of a poorly-soluble Chemical compound, compound. Their use is most prevalent in chemical and biological research relating to pharmaceuti ...

s such as

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

, and

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

. Typically poly(acrylamide)s such as poly(N-isopropylacrylamide) show the cononsolvency effect, while this effect is also known for other homopolymers and for more complex systems e.g., diblock copolymer,

polyelectrolyte Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Polycations and polyanions are polyelectrolytes. These groups dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are t ...

s, crosslinked microgels,

micelle A micelle () or micella () ( or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated colloidal system). ...

s, and grafted polymer brushes. Recently, it was also shown that thermo-responsive thin films exhibit the cononsolvency effect in a mixed solvent vapor phase, which can be explained by a decreased

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

phase

transition temperature In crystallography, the transition temperature is the temperature at which a material changes from one crystal state (allotrope) to another. More formally, it is the temperature at which two crystalline forms of a substance can co-exist in equili ...

, the

thin-film A thin film is a layer of materials ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many a ...

analogy of a

lower critical solution temperature The lower critical solution temperature (LCST) or lower consolute temperature is the critical temperature below which the components of a mixture are miscible in all proportions. The word ''lower'' indicates that the LCST is a lower bound to a te ...

. These experimental studies are supported by a growing number of simulation studies. After 45 years of research, the origin of the molecular mechanism behind the cononsolvency effect in a mixture of solvents remains not fully resolved yet. To date, researchers have considered various interactions between polymer and solvent/cosolvent as possible factors leading to the cononsolvency effect, such as competitive

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

ing of the solvent and cosolvent with the polymer,

hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

hydration of particular

functional group In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...

s of the polymer, cosolvent induced geometric frustration, excluded-volume interactions due to the surfactant-like behavior of amphiphilic cosolvents, as well as the three body effects, i.e., temporary bridging of one or more individual polymer chains by the cosolvent. In literature, cononsolvency was reported almost exclusively for polymers in aqueous solution. This, however, does not mean that cononsolvency cannot happen in non-aqueous solutions. For example, poly(methyl methacrylate) shows the cononsolvency effect in the binary mixtures of two organic solvents ( chlorobutane and

amyl acetate Amyl acetate (pentyl acetate) is an organic compound and an ester with the chemical formula CH3COO H2sub>4CH3 and the molecular weight 130.19g/mol. It is colorless and has a scent similar to bananas and apples. The compound is the condensation pr ...

References

{{Reflist Solvents Chemistry