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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

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        Author
        Filippov, Sergey K
        Bogomolova, Anna Yurevna
        Kaberov, Leonid
        Velychkivska, Nadiia
        Starovoytova, Larisa
        Cernochova, Zulfiya
        Rogers, Sarah E
        Lau, Wing Man
        Khutoryanskiy, Vitaliy V
        Cook, Michael T
        Attention
        2299/17369
        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 solid-like particles and chain network with a mesh size of 1-3 nm are present; nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have non-uniform 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 date
        2016-05-09
        Published in
        Langmuir : the ACS journal of surfaces and colloids
        Published version
        https://doi.org/10.1021/acs.langmuir.6b00284
        Other links
        http://hdl.handle.net/2299/17369
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        School of Life and Medical Sciences
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