Leveling agents are the "beautifiers" of coatings, capable of eliminating ridges and brush marks and giving the paint film a mirror-like effect. However, although the functions of oil-based (solvent-based) and water-based coating leveling agents are similar, they are fundamentally different due to "incompatibility", and must not be mixed.
The core difference lies in chemical compatibility. Oil-based coatings use organic solvents, and their leveling agents are mostly acrylic ester copolymers or unmodified organosilicon, which are hydrophobic and oleophilic and can be perfectly dissolved in the solvents. If added to a water-based system, they will immediately precipitate due to incompatibility, causing severe pinholes or even delamination in the paint film. Conversely, water-based coatings use water as the medium, and the surface tension of water is extremely high, so their leveling agents must undergo special "hydrophilic modification" (such as polyether-modified siloxane) to be stably dispersed in water and function properly.
The mechanisms of action also have different focuses. In the oil-based system, the surface tension of the solvent is low, and the leveling agent mainly relies on establishing a "surface tension gradient" to pull the paint liquid to flow and fill the depressions, with the focus being on controlling the rate of solvent evaporation. In the water-based system, the biggest challenge is the high surface tension of water. The leveling agent's primary task is to significantly reduce the tension to achieve wetting and spreading, and at the same time, it needs to suppress the surface turbulence (Bernard vortex) generated during the drying process to prevent the formation of hexagonal orange peel patterns.
In addition, water-based leveling agents are more prone to introducing foam, and often require the use of defoaming agents. Oil-based systems are less troubled by this. In summary, oil-based leveling agents are "hydrophobic" solvent companions, while water-based leveling agents are "hydrophilic" surface experts. Choosing the right leveling agent is not only about pursuing aesthetics but is also a crucial step in ensuring the performance of the coating. Remember: Take the right medicine for the right ailment to achieve a perfect paint surface.