Film Formation of Emulsion Polymers

Film formation is a process that converts the wet latex film into a solid polymeric film by evaporation of water after application of the coating material to the object to be coated. A continuous, tough polymeric film can form as a result of the film formation process. On the other hand, a powdery polymeric layer that eventually exhibits no mechanical strength is obtained if the film formation process is incomplete. Satisfactory film formation is a prerequisite for the coating materials to fully exhibit their excellent mechanical properties. Thus, to gain an insight into the mechanism of film formation is essential for assuring the primary performance of latex products. 

Devon et al. [33] prepared a series of acrylic latexes with core-shell particle morphologies. The minimum film formation temperatures (MFFT) of the latexes are expected to change with the core-shell characteristics in the following order  

Soft-hard (core-shell) medium-medium hard-soft 

Interesting enough, the above trend was confirmed experimentally only when the shell thickness was greater than a certain value. Thus, the latex particles with a thinner, softer shell surrounding a harder core required a higher temperature for successful film formation than that with a thicker shell with exactly the same polymer composition because more deformation was required to produce a continuous film for the former case. 

The collapse of foam is attributed to (a) the diffusion of gas molecules from a small bubble with higher internal pressure to a large one with lower internal pressure or into the bulk gas phase surrounding the foam system, (b) coalescence of bubbles due to capillary flow that results in rupture of the lamellar film between the adjacent bubbles (usually slower than (a) and occurring even in stabilized foam system), and (c) rapid hydrodynamic drainage of liquid between bubbles that leads to rapid collapse of bubbles [35], In most nonrigid foam systems, all three mechanisms are operative simultaneously to some extent during the foam collapse process. 

---