coalescence

Coalescence is a process where small particles merge to form a larger, continuous mass. In the context of surface coatings, this occurs when small polymer particles suspended in a liquid flow together to create a solid film.1

This process is crucial for forming polymer-based coatings. If the polymer particles are above their glass transition temperature, they are rubbery and can flow together naturally. If the polymer is below its glass transition temperature and in a rigid state, a "coalescent" (a solvent that softens the polymer) is added to help the particles merge. This coalescent then evaporates, leaving a solid film.1

This method is commonly used with latex polymers, primarily in water-based systems due to environmental regulations limiting organic solvents. It also applies to powder coatings, where solid paint particles melt and fuse together upon heating to form a continuous film.1