Observation of collapse and swelling of thermosensitive poly(N-isopropylacrylamide) brashes grafted on SiO₂

Thermosensitve poly(N-isopropylacrylamide) (PNIPAM) brushes grafted onto SiO₂-coated quartz crystal or glass surface were prepared with a surface-immobilized initiator. The microstructure of PNIPAM layer was examined by XPS, and AFM. Using QCM, we investigated the collapse and swelling of the brushes in water in real time. Frequency of PNIPAM brushes were found to gradually change throughout a temperature range 20-40°C, indicating that the PNIPAM brushes undergo a continuous transition. The nonuniformity and stretching of PNIPAM brushes as well as the cooperativity between collapse and dehydration transitions are thought to be responsible for the continuity.