The structure and volume phase transition behavior of poly(N-vinylcaprolactam)-based hybrid microgels containing carbon nanodots

In this paper, we investigated the internal structure and the volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-vinylimidazole)/polymerizable carbon nanodot (P(VCL-co-VIM)/PCND) microgels with different amounts of PCNDs. Our study shows that compared to the pure P(VCL-co-VIM) microgel, the hybrid microgels undergo a two-step VPT as the temperature increases and a core-shell(-corona) structure of the hybrid microgels is formed by copolymerization with PCNDs. A change in the amount of PCNDs has effects on both of the volume phase transition temperature and internal structure of microgels. Moreover, based on FT-IR in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectral (2Dcos) analyses, the difference in VPT behavior between the shell and the core (corona) structure of the hybrid microgels at the molecular level is elucidated. The core/shell of the hybrid microgels fixed with hydrophilic PCNDs has a higher transition temperature during heating and a more compact structure due to the additional crosslinkers PCNDs.