A FTIR and 2D-IR Spectroscopic Study on the Microdynamics Phase Separation Mechanism of the Poly(N-isopropylacrylamide) Aqueous Solution
Citations Over TimeTop 10% of 2008 papers
Abstract
The thermal behavior of PNIPAM in its concentrated D2O solution (20 wt %) was studied by FTIR and 2D-IR correlation spectroscopy. The spectral data of the C−H groups and the Amide I region provide details about the changes of the hydrophobic and hydrophilic parts in the polymer respectively during a heating−cooling cycle. The reversal of peak positions of the C−H bands upon cooling indicates the reversibility of temperature-induced dehydration of the hydrophobic groups. The change in hydrogen bonding of CO···D−N constructed between dehydrated CO and N−D groups, as derived from the Amide I region, does not revert precisely in the cooling process due to the newly formed hydrogen bonds in the collapsed state, and a hysteresis phenomenon is observed. In our concentrated solution (20 wt %), the strength of those intra- and interchain hydrogen bonds even prevent the polymers from dissociating completely below the LCST during the cooling process. The microdynamics phase separation mechanism was obtained by application of the 2D-IR analysis to the spectral data. When the temperature rises, the two-step dehydration of the CH3 groups occurs first, then the main-chain diffusion and aggregation takes place, and finally the hydrogen bond transition occurs. The dynamic sequence in the cooling process is also described.
Related Papers
- → Assembly Pattern of Supramolecular Hydrogel Induced by Lower Critical Solution Temperature Behavior of Low-Molecular-Weight Gelator(2019)77 cited
- → LCST‐Type Hyperbranched Poly(oligo(ethylene glycol) with Thermo‐ and CO2‐Responsive Backbone(2018)16 cited
- → Formulation and synthesis of hydrogels having lower critical solution temperature near body temperature(2017)1 cited
- Controllable release of ibuprofen from thermo-sensitive poly(N-isopropylacrylamide) hydrogel(2011)
- → Properties of polymer blends above the lower critical solution temperature (LCST)(1992)