Using a combination of static and dynamic light scattering

we systematically studied the coil-to-globule and globule-to-coil transitions of a single linear poly (Nisopropylacrylamide) (PNIPAM) chain and the volume change of spherical PNIPAM microgels in water.We made

for the first time

the conformation change of individual homopolymer chains from a coil to a fully collapsed stable single-chain globule and confirmed the existence of the crumpled coil and the molten globule states between the random coil and the fully collapsed globular states.The study of the coil-to-globule transition kinetics rejects the previously suggested high chain-knotting density inside the globule.Our result also indicated that even in its fully collapsed state

the globule and the microgel particle still contain 66% and 70% water

respectively.The study of interaction between the PNIPAM microgel and surfactant suggested a new swelling and shinking mechanism different from the previously proposed hydrophobic interaction.Moreover

our NMR results showed

for the first time

that surfactant molecules are able to form micelles in presence of the gel network even the surfactant concentration is much lower than its critical micelle concentration.A comparison of the phase transitions of the linear chains and microgels revealed that previously observed discontinuous volume change in bulk PNIPAM gels is due to the imbalance between the bulk shear module and the internal stress originated from the inhomogeneous shrinking

which is different from the theoretically predicted discontinuous volume phase transition.