In Situ Dissolution and Swelling of Confined Lamellar Polymer Crystals through Exposure to Humid Air

Abstract

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.

Tracking the Dissolution Surface Kinetics of a Single Fluorescent Cyclodextrin Metal–Organic Framework by Confocal Laser Scanning Microscopy

“…In 60 and 70% methanol aqueous solutions, the value of n is 0.3304 and 0.2630 ( n < 0.45) for the dissolution of the CD-MOF⊃FL crystal, respectively, implying that the dissolution of the CD-MOF⊃FL crystal maintained a Fickian behavior (case I transport) governed by tiny swelling and diffusion . In 75% methanol aqueous solution, n is 0.745 (0.45 < n < 0.89), indicating that the dissolution of the CD-MOF⊃FL crystal followed a non-Fickian behavior, controlled by both diffusion and erosion. , In 80 and 95% methanol aqueous solutions, n is 1.037 and 4.927 ( n > 0.89), respectively, indicating that the dissolution of the CD-MOF⊃FL crystal exhibited a Fickian behavior (case II transport) controlled by erosion …”

“…50,52 In 80 and 95% methanol aqueous solutions, n is 1.037 and 4.927 (n > 0.89), respectively, indicating that the dissolution of the CD-MOF⊃FL crystal exhibited a Fickian behavior (case II transport) controlled by erosion. 53 Additionally, the size influence on the dissolution kinetics was studied by comparing the dissolution kinetics of 160 and 80 μm CD-MOF⊃FL crystals. It takes ca.…”

“Printing” on Polymer Single Crystals through Microregional Heating

“…After total evaporation of solvent (evaporation time ≈ 20 min), we found that a lot of square-shaped structures had emerged on the substrate. Square-shaped platelets represent classical patterns of PEG single crystals. ,, From the changes in the corresponding gray value plots of the intensity emitted from the AIE groups, we followed the crystallization process in the thin film solution. The number density of polymers at locations close to the edge of the substrate was higher, probably due to the so-called “coffee-ring effect”, resulting in an accumulation of PEG aggregates close to the edge of the substrate.…”

“Printing” on Polymer Single Crystals

“…Square-shaped platelets represent classical patterns of PEG single crystals. 17,30,31 From the changes in the corresponding grey value plots of the intensity emitted from the AIE groups, we followed the crystallization process in the thin lm solution. The number density of polymers at locations close to the edge of substrate was higher, probably due to the so-called "coffee-ring effect", resulting in an accumulation of PEG aggregates close to the edge of the substrate.…”