Study on Self-Assembly of Telechelic Hydrophobically Modified Poly(N-isopropylacrylamide) in Water
The microscopic structures of aqueous dispersions of hydrophobically modified poly(N-isopropylacrylamides) (HM-PNIPAM) and hydrophobically modified poly(ethylene oxide) (HM-PEO), which carry an octadecyl group at each chain end and have an average molecular weight of 20,000 g/mol, were investigated by small-angle neutron scattering (SANS). When the polymer concentration exceeds the overlap concentration, connectivity through bridging chains takes place, resulting in the formation of a network in which flower micelles act as junctions. The temperature dependence of the micelle structure is significant in the case of the HM-PNIPAM system but not significant in the case of the HM-PEO system, indicating the importance of hydrophobic interactions in the structural stability of flower micelles. Two different parameters relating to the micelle size are defined depending on the polymer concentration. One is the total micelle radius in the dilute regime and the other is the "non-overlapping radius" of the micelles in the semi-dilute regime. These two parameters exhibit qualitatively different trends with respect to temperature.
KeywordsPoly(N-isopropylacrylamides) Poly(ethylene oxide) Telechelic Hydrophobically Modified Polymer Inter-Micellar Network Small-Angle Neutron Scattering
The work was partly supported by a Grant-in-Aid for Scientific Research on Priority Areas “Soft Matter Physics” (No. 19031024) and by a Grant-in-Aid for the Global COE Program, "Science for Future Molecular Systems" from the Ministry of Education, Culture, Science, Sports and Technology of Japan. SANS experiments were performed with the approval of the Institute for Solid State Physics, The University of Tokyo (Proposal No. 7404) and the approval of the Neutron Science Laboratory (KENS) at the High Energy Accelerator Research Organization (KEK) (Proposal No. 2005B1-008). Authors acknowledge Prof. Tanaka and Dr. Koga (Kyoto University) for valuable discussion.