Publications

Characterization of free, restricted, and entrapped water environments in poly(N-isopropyl acrylamide) hydrogels via 1H HRMAS PFG NMR spectroscopy

Alam, Todd M.; Childress, Kimberly K.; Pastoor, Vevin; Rice, Charles V.

Different water environments in poly(N-isopropyl acrylamide) (PNIPAAm) hydrogels are identified and characterized using 1H high resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR). Local water environments corresponding to a "free" highly mobile species, along with waters showing restricted dynamics are resolved in these swollen hydro-gels. For photo-initiated polymerized PNIPAAm gels, an additional entrapped water species is observed. Spin-spin R2 relaxation experiments support the argument of reduced mobility in the restricted and entrapped water species. By combining pulse field gradient techniques with HRMAS NMR it is possible to directly measure the self-diffusion rate for these different water environments. The behavior of the heterogeneous water environments through the lower critical solution temperature transition is described.