Film formation from monodisperse acrylic latices

The influence of concentration and layer thickness on particle ordering in polymer latex films, both open and closed, has been studied by means of rheology, microscopy and turbidimetry. Monodisperse acrylic latices were synthesized by semicontinuous emulsion polymerization. The latices exhibited a distinct thixotropy above a certain concentration, which is attributed to crystallization. Microscopy revealed a three-layer structure and a dependence of crystal size and crystal packing on layer thickness and layer concentration. Turbidimetry (i.e., analysis of light transmission and interference) was used to study the progress of ordering in open and closed systems. In closed films crystallization proceeds faster at higher concentrations and in thinner films. Above a sufficiently high concentration no crystallization was observed. Furthermore, an induction time was found below certain concentrations. The drying of open latex films at temperatures below the minimum film formation temperature (MFFT) was shown to proceed through five distinct stages. The drying of open films at temperatures below the MFFT was studied by analysis of the turbidity of rewetted films. A more compact structure was found in thinner films. The structure in latices is discussed as a result of long-range and short-range ordering.