SYNOPSISThis work describes the synthesis of model latices devoted to the study of the influence of pafticle-water and particle-air interfacial energies on coalescence mechanisms. Core-shell particles with the same diameter ( N 2600 A ) and narrow size distributions were prepared.The core is a poly( styrene-co-butyl acrylate) (60/40 wt % ) copolymer; it represents 90% of the volume of the particle. The shell is a poly(St-BuA-methacrylic acid) terpolymer with 10, 15, or 25 wt % MAA. The St-BuA weight ratio in the shell is also 60/40. The amount of MAA in the shell determines the particle-water or air interfacial energies. In order to limit the use of an emulsifier and to ensure a homogeneous particle surface layer, an inverted core-shell synthesis was performed. The hydrophilic shell was prepared first and used as a seed for the synthesis of the hydrophobic core. For all three core-shell latices, about 45% of the introduced MAA was found at the surface of the particles, which indicates that the core-shell inversion was successful. The synthesis of the latices with 10 or 15 wt % MAA was relatively easy, whereas the particle size was difficult to control in the 25 wt % MAA latex synthesis.
I NTRO DU CTl O NThe understanding of coalescence mechanisms of polymer colloids is of major practical importance and fundamental interest. Several authors have tackled the problem in the past.'-' Recently, Dobler et a1.6 reviewed the literature on this subject. It appeared that more work was needed in order to reach a satisfactory level of knowledge of the phenomenon. This study describes the synthesis of model latices devoted to further studies of coalescence mechanisms.The following are the most important parameters that influence the coalescence mechanisms: the particle diameter, the water-air, particle-water, and particle-air interfacial energies, the colloidal stability at small interparticular distances, and the viscoelastic properties of the polymers. The temperature and relative humidity conditions are also of great importance in the phenomenon. We were mainly interested in the study of the influence of * To whom correspondence should be addressed. interfacial energies on the coalescence process. It is necessary to vary one parameter without affecting the others. Thus, we had to synthesize monodispersed latices with the same particle diameter, the same viscoelastic properties but different particlewater and air interfacial energies. The monomers we used were styrene ( S t ) , butyl acrylate (BuA) and methacrylic acid (MAA) . Different particlewater and air interfacial energies were achieved by varying the amount of MAA in the outermost surface layer of the particles. The higher the MAA content at the surface, the lower the interfacial energy with water. Homogeneous particles with different amounts of MAA would have different viscoelastic properties especially in water, which acts as a plasticizer in MAA-containing polymers. It was then necessary to produce core-shell particles. In our case the core represents 90% of the t...
