Molecular dynamics of poly(N-vinylcaprolactam) hydrate

Poly(N-vinylcaprolactam)-D2O has been studied by Neutron Spin Echo (NSE) in the temperature range from -60degreesC to +40degreesC. Hydration (similar to 7 D2O molecules per chain unit) transforms the rigid-chain polymer into an elastomer, making the glass-transition temperature drop from T-G = 147degreesC (dry polymer) to T-G = -20degreesC. The hydration shell, created by hydrogen bonds of water, molecules with C=O groups, remains stable up to similar to 50degreesC. The molecular mobility is enhanced by the addition of water, showing a maximum in the window T = - 20 to +5 degreesC. The anomalous dynamics was studied in the time domain t = 0.003-5 ns (momentum transfer q = 0.55 nm(-1)), and demonstrated the hybridisation of transversal modes and reptations of the chains.