Polymer hydration and microphase decomposition in poly( N ‐vinylcaprolactam)–water complex

Poly( N ‐vinylcaprolactam) (PVCL) is a synthetic analogue of biomolecules (enzymes, proteins). It demonstrates a specific hydration and undergoes a coil–globule transition. The PVCL–D 2 O system (PVCL mass M = 10 6 ) has been investigated by small‐angle neutron scattering (SANS) at T = 296–316 K to identify the structural features of the collapse at concentration C = 0.5 wt% near the threshold of the coil overlap. (The collapse leads to the segregation of the phase enriched with polymer at T > 305 K). The SANS experiments at q = 0.1–5 nm −1 (scales from monomer unit to globule gyration radius R G ≃ 16 nm) have revealed a stretched coil–globule transformation in the range 305–309 K. Using high‐resolution SANS ( q = 0.002–0.02 nm −1 ) the globule association to form fractal structures (sponge‐like) of surface dimension D F ≃ 2.4–2.6 was examined. The coexistence of globules and disordered chains (regions ∼5–10 nm) was found. The growth of the content of globular phase was induced by the conformational transition in disordered molecular fragments from coiled (dimension D ≃ 1.8) to stretched chains ( D ≃ 1.2).