Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 17, Issue 38, Pages 25525-25535Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c5cp03676c
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Funding
- National Science Foundation of China (NSFC) [21274030, 51473038, 21274025]
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Thermo-dynamic volume phase transition mechanisms of poly[oligo(ethylene glycol) methacrylate] (POEGMA) based microgels with poly(ionic liquid) (PIL) cross-linking moieties are investigated in detail on the basis of temperature-dependent Fourier transform infrared (FTIR) spectroscopy. The original FTIR data are further analysed by two-dimensional correlation spectroscopy (2Dcos) with the perturbation correlation moving window (PCMW) technique. It is observed that the content of hydrophilic PIL cross-linking structure strongly affects the temperature induced volume phase transition mechanism of microgels in which the less cross-linked microgel exhibits a sharp volume phase transition process while the highly cross-linked microgel presents a broad transition behavior. Peculiarly, the dehydration of C-H groups acts as the driving force for the whole phase transition process within the less cross-linked microgel network and cooperative response of chemical groups is identified. It is deduced that the hydrophilic PIL moieties develop polymer-water-polymer interactions with C=O groups as C=O center dot center dot center dot D2O-PIL hydrogen bonds emerge in the less cross-linked system. As regards the highly cross-linked microgel system, the phase transition process is driven by the disruption of hydrogen bonds between CQO groups and water molecules while the response of C-H groups becomes insensitive. PIL moieties passively dehydrate following the dehydration of C-H groups on oligo(ethylene glycol) side chains and no hydrogen bond between CQO group and IL-D2O association appears during the phase transition process.
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