The effect of bimodality of the particle size distribution on film formation of latices

Abstract

The effect of a bimodal particle size distribution on the film formation behaviour of latex blends was studied by means of atomic force microscopy and minimum film formation temperature (MFFT) measurements. Monodisperse latices of butyl methacrylate, ranging from 172 to 1797 nm in diameter, were prepared by means of a surfactant-free emulsion polymerization, in order to exclude effects related to surfactant migration or molecular weight. The only differences between the recipes were the solids contents of the latex. When using blends of these latices, it was found that the addition of small amounts of small particles to larger particles has almost no effect on the MFFT of the latex, but can have an enormous effect on the particle matrix packing when drying the blend below its MFFT. Usually, the addition of increasing amounts of small particles leads to a disruption of the particle matrix until the point, at which the matrix changes from a continuous matrix of large particles into a continuous matrix of small particles. No clear distinction could be made between the case where the small particles will fit into the voids of the continuous matrix of large particles and the case where they do not. The investigation shows that when mixing particles of different size, the particle matrix is affected but that this does not necessarily influence the MFFT.