Water as a probe for the temperature-induced self-assembly transition of an amphiphilic copolymer

The hydration state of amphiphilic block copolymers during the self-assembly transition is closely related to the structure and properties of copolymers. In this study, the temperature-induced self-assembly of copolymer poly(N,N-dimethylacrylamide)-poly(diacetone acrylamide) (PDMAA₃₀-PDAAM₆₀)₂ in aqueous solution was monitored by near-infrared spectroscopy with water as a probe. The wavelet packet transform was employed to improve the spectral resolution. The spectral information of hydrated water surrounding the hydrophilic PDMAA and hydrophobic PDAAM blocks was then extracted, revealing the significant roles of water in morphological transition of the copolymer from spherical to worm-like micelles. Specifically, water molecules interacting with N atoms and C=O groups of the hydrophilic block gradually decrease during the morphological transition, while hydrogen-bond structures NHCO of the hydrophobic block gradually break, bringing more water molecules into contact with the hydrophobic block. This work provides a foundation for exploring the role of water molecules during the self-assembly transition of complex block copolymers.