首页|In Situ Dissolution and Swelling of Confined Lamellar Polymer Crystals through Exposure to Humid Air
In Situ Dissolution and Swelling of Confined Lamellar Polymer Crystals through Exposure to Humid Air
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NSTL
Amer Chemical Soc
Using a hydrophobic-hydrophilic poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer, we formed sandwich-like micron-sized thin platelets via crystallization in solution. These platelets consisted of a crystalline PEO lamella confined between two glassy PS layers and were deposited on a solid substrate. Using in situ optical microscopy, we followed the temporal and spatial changes in the thickness and morphology of these sandwich-like platelets induced by exposure to humid air. As water is a good solvent for PEO but a nonsolvent for PS, we observed first the dissolution of the confined crystalline PEO layers characterized by a sharp dissolution front propagating at an almost constant velocity as expected for case II diffusion into a solid. The resulting hydrated PEO brushes absorbed water further until equilibration of the respective chemical potentials, accompanied by a change from a planar to a dome-shaped morphology that could be fully reversed by exposure to dry air. Repeated swelling-deswelling cycles demonstrated stability and reproducibility of these developments taking place at distinctly different transport rates. Here, we discuss the underlying processes of water permeation into and efflux from the PEO layers.
NSTL
Amer Chemical Soc
