Molecular and environmental aspects of latex film formation

grantor: University of TorontoThis thesis examines mainly the formation mechanism and structure of latex films. We investigated the drying behavior of latex dispersions by monitoring simultaneously the loss of water mass and the contraction of the wet dispersion area. A soft latex dries slower than a hard latex, and their blends dry even more slowly. The presence of hydrophilic material facilitates drying. We propose a drying model to explain the results. We examined our strategy for zero VOC (volatile organic compound) coatings, by blending latex particles of a low Tg polymer (e.g., poly(butyl methacrylate-co-butyl acrylate)) and of a high Tg polymer (e.g., poly(methyl methacrylate)). Transparent films can be obtained from blend dispersions when the volume fraction of soft polymer exceeds a critical value $(\Phi \sb{\rm C)}$ ca. 0.5, and when the hard spheres are uniformly distributed in a soft polymer matrix. The hard particles in blends improve significantly the mechanical properties. Interface structure in blend films was characterized by direct non-radiative energy transfer (DET) technique. A finite efficiency of DET, which is proportional to the interfacial area, characterizes a sharp interface between the polymer components, and its slight increase upon annealing the films represents the evolution of interface thickness (up to 7 nm at 140$\sp\circ$C). The DET technique is also employed to analyze polymer diffusion in latex films and to examine the effect of various components on diffusion rate. We find that water has little effect on the diffusion of a hydrophobic polymer (poly(butyl methacrylate), PBMA). For a hydrophilic polymer (a copolymer of BMA with 5 wt% methacrylic acid), the presence of water increases the diffusion coefficient by a factor of 5 in the protonated sample, and by 2 orders of magnitude for the sample neutralized by a base (e.g., NaOH). The BMA oligomers enhance significantly the diffusion rate of high molar-mass PBMA. Finally, we examine strategies for ambient crosslinking of latex films. Films with acetoacetoxy functionality can be crosslinked rapidly with diamine as a crosslinker. Films with unsaturated bonds can be cured with the addition of an organic salt (e.g., cobalt octoate) m several days during which a high degree of polymer interdiffusion can be achieved.Ph.D