Reentrant coil-to-globule-to-coil transition of a single linear homopolymer chain in a Water/Methanol mixture

Both water and methanol are good solvents for poly(N-isopropylacrylamide) ( PNIPAM) at room temperature, but strangely not a mixture of them. Using nar rowly distributed linear PNIPAM chains (M-w = 2.6 x 10(7) g/mol and M-w/M-n < 1.1), we have, for the first time, observed a coil-to-globule-to-coil tr ansition of a single PNIPAM chain when methanol was gradually added into wa ter. This novel reentrant transition leads to insight into the complexation between methanol and water. We also found that the chain was crumpled in i ts globule state and the globule still contained <similar to>80% of solvent in its hydrodynamic volume.