Structural Study on the UCST-Type Phase Separation of Poly(<i>N</i>-isopropylacrylamide) in Ionic Liquid

Abstract

Upper critical solution temperature (UCST)-type phase separation behavior and its conformational change of well-defined poly(N-isopropylacrylamide) (pNIPAm) in deuterated room-temperature ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (d8-[C2mIm+][TFSA–]), were investigated by means of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. From the temperature dependence of time-averaged scattering intensity obtained by DLS, it was found that the cloud points of pNIPAm/d8-[C2mIm+][TFSA–] solutions increased with molecular weight (Mw) and concentration. In addition, it was found that there are two relaxation modes of pNIPAm in the IL solutions. From SANS measurements, the radius of gyration, Rg, and the Flory–Huggins interaction parameter, χ, were evaluated as a function of temperature during the phase separation.