Theoretical modelling of hierarchically associated structures in hydrophobically modified PNIPAM aqueous solutions on the basis of a neutron scattering study

古賀 毅*; 田中 文彦*; 元川 竜平; 小泉 智*; Winnik, F. M.*

Macromolecular Symposia, 291-292(1), p.177 - 185, 2010/05

https://doi.org/10.1002/masy.201050521

We developed a theoretical model for a self-assembling telechelic poly(Nisopropylacrylamide) (PNIPAM) carrying octadecyl end-groups in aqueous solution, as a function of temperature and concentration, on the basis of small-angle neutron scattering data. In solutions of concentration 10 gL at temperatures between 10 and 20 C, the telechelic PNIPAM of molecular weight of 22200 gmol associates in the form of flower micelles containing about 12 polymer chains. Micelles have a 3-layered core-shell morphology with an inner core consisting of the octadecyl units, a dense inner shell consisting of partly collapsed PNIPAM chains, and an outer shell of swollen hydrated PNIPAM chains. Drastic changes in the scattering profile of the solution heated above 31 C are attributed to the formation of mesoglobules of diameter of 100 nm consisting of about 1000 polymer chains. In solutions of lower concentration (1 gL), association of flower micelles and mesoglobules is suppressed. The structure of the individual flower micelles and mesoglobules is not affected by changes in concentration. In solutions of 50 gL, a peak attributed to a correlation between flower micelles appears in the scattering profiles at low temperature (10 C). Despite the difference in the population of intermicellar bridges, the overall temperature dependence of the scattering profile at 50 gL remains similar to that at 10 gL.