Polymer interdiffusion between latex particles during film formation is studied using the fluorescence technique of nonradiative energy transfer (NET). Model emulsion polymers of poly(butyl methacrylate) and poly(amyl methacrylate), labeled with the energy transfer pair of 1-naphthylethyl methacrylate or 9-anthryl methacrylate, are investigated. The effects of particle size, polymer glass transition temperature, and polymer compatibility on the rate and extent of interparticle diffusion are measured. In addition, the time dependence of transmission electron microscopy images during the final stage of film formation augments the conceptual picture of interdiffusion. A change in particle size is observed to enhance the intermixing rate in proportion to the particle surface area to volume ratio, while leaving the apparent diffusion coefficient unchanged. The dependence of the diffusion coefficient on temperature is adequately described by both the WLF and Arrhenius equations, albeit throughout a comparatively narrow temperature range, and the activation energies were found to be equivalent within experimental error for the two acrylates.
Film formation from a latex involves interdiffusion of polymer chains. The interdiffusion behavior of polystyrene with H ends, one sulfonate end, and two sulfonate ends are compared via smallangle neutron scattering (SANS) and a direct nonradiative energy transfer technique (DET) at short times. High molecular weight (M n = 300 000) anionically synthesized polystyrenes were confined in latex particles utilizing an artificial miniemulsification technique. Interdiffusion of the polystyrenes in a latex film was carried out at temperatures of 125-145 °C. The diffusion coefficients of polystyrene with H ends were five times and 10 times higher than that of polystyrene with one sulfonate end and two sulfonate ends, respectively. The probable cause is end-to-end aggregation of the chains, supported by the ratio R g/M 1/2 remaining substantially constant.
Using a direct energy transfer method, ionic end groups on polystyrene were found to increase the early-time apparent interdiffusion coefficients during film formation. The early-time apparent diffusion coefficients of polystyrene with varying end groups were found to follow the ordering of SO4 > COOH > H. The higher apparent diffusion coefficients are presumably due to the surface segregation of the end groups caused by the polar, aqueous environment during latex synthesis. By titration, 60% of the sulfate end groups and 30% of the carboxyl end groups were found on the latex particle surfaces. The apparent diffusion coefficients at very early times are separable into two additive values: that arising from the polymer chains with chain ends on the latex surface, and that caused by polymer with chain ends buried in the latex interior. The present experiments suggest that the location of the end group is the critical factor determining the initial apparent diffusion coefficients of the polymers rather than the characteristics of the end groups themselves.
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