The onset of polymer diffusion in a drying acrylate latex: how water initially retards coalescence but ultimately enhances diffusion |
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Authors: | Jeffrey C Haley Yuanqin Liu Mitchell A Winnik Willie Lau |
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Affiliation: | (1) Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON, Canada, M5S 3H6;(2) Rohm and Haas Company, 727 Norristown Rd., Spring House, PA 19477, USA |
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Abstract: | The diffusion of polymer chains across the interface between distinct latex particles is the final step in latex film maturation.
This step drives the transformation of a honeycomb of compacted latex particles bound by weak surface forces into a mechanically
robust film. Knowledge of the onset of this diffusion process is limited. We have examined film formation in butyl acrylate-methyl
methacrylate copolymer latex containing 1 wt% methacrylic acid. These films dry via a propagating drying front. We were able,
via fluorescence resonance energy transfer measurements, to determine the extent of polymer interdiffusion at 23°C as a function
of distance from the edge of the drying front for a series of partly wet latex films. Our apparatus allows us to arrest the
latex drying process and to extract interdiffusion information from sub-millimeter regions of the drying film. We have tracked
the latex drying process and subsequent polymer diffusion as a function of humidity. We find that adjacent to the drying front,
increasing humidity initially delays the onset of interdiffusion, but once this initial barrier is overcome increasing humidity
increases the rate of diffusion. This transition occurs within 1–2 mm of the drying front.
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Keywords: | Fluorescence resonance energy transfer Hydroplasticization Film formation Poly(methyl methacrylate) Poly(butyl acrylate) |
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