At this point a strongly repulsive interaction dominates. This results in an optimal distance of separation that is called van der Waals contact distance. This is the distance that is used when constructing space filling models. The van der Waals interactions are often modeled by the following equation. Water as solvent .
Water is an excellent solvent of polar groups.
Water is a poor solvent of non-polar groups. Non-polar groups have a tendency to associate in solution. This description is not entirely accurate. This translates to a decrease in the entropy of the water surrounding a non-polar group. When non-polar groups associate, they remove some of their surface from exposure to water.