| Abstract: | Different polymer latices are often incompatible, even when the emulsifying agent is the same in each. If one polymer has a proportion of hydrophilic groups (type ?A”? latex) and the other does not (type ?S”? latex), a mixture of the two latices may coagulate within seconds of mixing. Quite small proportions of type ?A”? will cause agglomeration of the particles of a type ?S”? latex. If 1% of a latex prepared from ethyl acrylate and acrylic acid (95:5) is added to a poly(butylacrylate) latex, D?w, = 800 Å, and the pH is adjusted to 8–9, the resulting latex is characterized by D?n, = 6300 Å, D?w, = 7300 Å; addition of any given type ?S”? latex increases the average particle size still more. The mechanisms involved were studied by observing changes in particle size distribution, by the use of polymerizable dyes as markers, and by electron microscopy. The results of these investigations are : The latices are protected only in some respect by the emulsifier. The protective ionic doublelayer formed by the emulsifier around a type ?S”? particle repels other particles, but not type ?A”? particles. If a collision occours between particles of type ?A”? und type ?S”? they stick together; this process is repeated as often as a type ?S”? particle hits the surface of ?A”?. All the type ?S”? particles of the associate combine to one big particle in such a way that the ?A”? particle stays at the surface and remains active for further agglomeration. |
