How do latex paints form a continuous polymer film?

Latex paints form a continuous polymer film through a process known as coalescence.

In this process, small polymer particles—typically ranging from 0.05 to 1.0 micrometres—are suspended in water. As the water evaporates after the paint is applied to a substrate, these particles are brought together and flow into one another due to surface-mediated forces, eventually fusing into a solid, continuous film.1

For this to occur effectively, the polymer must be in a rubbery state, meaning it is above its glass transition temperature (T_g). If the polymer is in a rigid, glassy state (below its T_g), manufacturers add a coalescent—a solvent that temporarily plasticizes the polymer to lower its effective T_g. Once the film has formed, this coalescent evaporates, leaving behind the final solid coating.1