Theoretical Modelling of Hierarchically Associated Structures in Hydrophobically Modified PNIPAM Aqueous Solutions on the Basis of a Neutron Scattering Study

Abstract

AbstractWe developed a theoretical model for a self‐assembling telechelic poly(N‐isopropylacrylamide) (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 g L−1 at temperatures between 10 and 20 °C, the telechelic PNIPAM of molecular weight of 22,200 g mol−1 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 g L−1), 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 g L−1, 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 g L−1 remains similar to that at 10 g L−1.