TY  - JOUR
A1  - Nieuwenhuis, Sophie
A1  - Zhong, Qi
A1  - Metwalli, Ezzeldin
A1  - Biessmann, Lorenz
A1  - Philipp, Martine
A1  - Miasnikova, Anna
A1  - Laschewsky, Andre
A1  - Papadakis, Christine M.
A1  - Cubitt, Robert
A1  - Wang, Jiping
A1  - Müller-Buschbaum, Peter
T1  - Hydration and Dehydration Kinetics: Comparison between Poly(N-isopropyl methacrylamide) and Poly(methoxy diethylene glycol acrylate) Films
JF  - Langmuir
N2  - Thermoresponsive films of poly(N-isopropyl methacrylamide) (PNIPMAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) are compared with respect to their hydration and dehydration kinetics using in situ neutron reflectivity. Both as-prepared films present a homogeneous single-layer structure and have similar transition temperatures of the lower critical solution temperature type (TT, PNIPMAM 38 degrees C and PMDEGA 41 degrees C). After hydration in unsaturated D2O vapor at 23 degrees C, a D2O enrichment layer is observed in PNIPMAM films adjacent to the Si substrate. In contrast, two enrichment layers are present in PMDEGA films (close to the vapor interface and the Si substrate). PNIPMAM films exhibit a higher hydration capability, ascribed to having both donor (N-H) and acceptor (C=O) units for hydrogen bonds. "While the swelling of the PMDEGA films is mainly caused by the increase of the enrichment layers, the thickness of the entire PNIPMAM films increases with time. The observed longer relaxation time for swelling of PNIPMAM films is attributed to the much higher glass transition temperature of PNIPMAM. When dehydrating both films by increasing the temperature above the TT, they react with a complex response consisting of three stages (shrinkage, rearrangement, and reswelling). PNIPMAM films respond faster than PMDEGA films. After dehydration, both films still contain a large amount of D2O, and no completely dry film state is reached for a temperature above their TTs.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.langmuir.9b00535
SN  - 0743-7463
VL  - 35
IS  - 24
SP  - 7691
EP  - 7702
PB  - American Chemical Society
CY  - Washington
ER  -