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Internal Nanoparticle Structure of Temperature-Responsive Self-Assembled PNIPAM-b-PEG-b-PNIPAM Triblock Copolymers in Aqueous Solutions: NMR, SANS, and Light Scattering Studies

Lookup NU author(s): Dr Wing Man LauORCiD

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Abstract

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.

Publication metadata

Author(s): Filippov SK, Bogomolova A, Kaberov L, Velychkivska N, Starovoytova L, Cernochova Z, Rogers S, Lau WM, Khutoryanskiy VV, Cook MT

Publication type: Article

Publication status: Published

Journal: Langmuir

Year: 2016

Volume: 32

Issue: 21

Pages: 5314–5323

Print publication date: 31/05/2016

Online publication date: 09/05/2016

Acceptance date: 03/05/2016

Date deposited: 18/01/2018

ISSN (print): 0743-7463

ISSN (electronic): 1520-5827

Publisher: American Chemical Society

URL: https://doi.org/10.1021/acs.langmuir.6b00284

DOI: 10.1021/acs.langmuir.6b00284

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