Internal nanoparticle structure of temperature-responsive self-assembled PNIPAM-b-PEG-b-PNIPAM triblock copolymers in aqueous solutions: NMR, SANS, and light scattering studies

0460134 - ÚMCH 2017 RIV US eng J - Journal Article
Filippov, Sergey K. - Bogomolova, Anna - Kaberov, Leonid I. - Velychkivska, Nadiia - Starovoytova, Larisa - Černochová, Zulfiya - Rogers, S. E. - Lau, W. M. - Khutoryanskiy, V. V. - Cook, M. T.
Internal nanoparticle structure of temperature-responsive self-assembled PNIPAM-b-PEG-b-PNIPAM triblock copolymers in aqueous solutions: NMR, SANS, and light scattering studies.
Langmuir. Roč. 32, č. 21 (2016), s. 5314-5323. ISSN 0743-7463
R&D Projects: GA ČR(CZ) GC15-10527J
Institutional support: RVO:61389013
Keywords : nanoparticles * copolymers * NMP
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.833, year: 2016

In this study, we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR spectroscopy, light scattering, and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solidlike particles and chain network with a mesh size of 1–3 nm are present, nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have nonuniform structure with “frozen” areas interconnected by single chains in Gaussian conformation. SANS data with deuterated “invisible” PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation.
Permanent Link: http://hdl.handle.net/11104/0260271