Solvation effects
Last modified: 20.11.23
What is solvation? Solvation is an interaction of a solute with a solvent. I.e. it is the different interactions that occur when you dissolve or try to disolve something. A common term that refers to solvation of water is hydration.
Molecules dissolve when the interactions between the solid molecule and the solvent (or liquid) are strong enough to favour the deformation of the solid. There are many reasons why molecules will dissolve and it has to do with the chemical structure of the compound - the more structurally similar the compound is to the solvent, the more likely it will dissolve. For example, methanol consisting of CH2OH will dissolve in water H2O, due to the hydrogren bonding interactions.
Without getting too complicated, oxygen of water likes to pull the electron density of hydrogens making it slightly negatively charged, while the hydrogens exhibit slightly positive charges. This property allows compounds such as salt to dissolve. Salt or NaCl - is an ionic compound that is formed through interactions between a positve sodium Na+ and negative chloride Cl-. This compound dissolves in water as the ionic nature of water solvates the ionic charges of sodium and chloride.
Hydration in organic chemistry Many organic compounds exist of aromatic or alkyl groups. These functional groups consist of mostly carbon and hydrogen groups which do not interact well with water. Therefore, most organic compounds do not dissolve in water. Instead of exhibiting hydrogen bonds or ionic groups that can interact with water, they exhibit Van der Waals interactions. These interactions are weak non-ionic interactions that occur between carbon and hydrogen functionality. Thus, these molecules can only be dissolved by solvents that also exhibit Van de Waals interactions: such as petroleum or hydrocarbon based solvents.
The impact of solvation on polymers Polymers are organic compounds. Therefore, like organic compounds, polymers readily dissolve in hydrocarbon based solvents, and rarely dissolve in water. However,polymer dissolution is not the only consequence of solvation.
When a polymer is dissolved in a solvent, the interactions between the solvent and the polymer will determine the morphology and conformation of the polymer.[1] For example, when a polymer is dissolved in a good solvent, the polymer interactions are maximised and produce a denser structre. While from a poor solvent, interactions between polymer chains are limited, the polymer aggregates and produces a more porous structure.[2]
Polyelectrolytes Unlike most other polymers, polyelectrolytes usually readily dissolve in water. They consist of ionic groups or charges which attract to water molecules, allowing dissolution in water.
References [1] Satake, A. The Solvent Effect on Weak Interactions in Supramolecular Polymers: Differences between Small Molecular Probes and Supramolecular Polymers. ChemPlusChem 2020, 85 (7), 1542-1548. [2] Krokhina, L. S.; Kuleznev, V. N.; Lyusova, L. R.; Glagolev, V. A. Effect of solvent on polymer interaction in solution and properties of films obtained. Polymer Science U.S.S.R. 1976, 18 (3), 756-762.