title: Internal Nanoparticle Structure of Temperature-Responsive Self-Assembled PNIPAM-b-PEG-b-PNIPAM Triblock Copolymers in Aqueous Solutions: NMR, SANS, and Light Scattering Studies.
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.
authors.affiliation: Institute of Macromolecular Chemistry , AS CR, Heyrovsky Sq. 2, Prague, Prague 6, 162 06, Czech Republic.
authors.forename: Sergey K
authors.initials: SK
authors.lastname: Filippov
authors.affiliation: Institute of Macromolecular Chemistry , AS CR, Heyrovsky Sq. 2, Prague, Prague 6, 162 06, Czech Republic.
authors.forename: Anna
authors.initials: A
authors.lastname: Bogomolova
authors.affiliation: Institute of Macromolecular Chemistry , AS CR, Heyrovsky Sq. 2, Prague, Prague 6, 162 06, Czech Republic.
authors.forename: Leonid
authors.initials: L
authors.lastname: Kaberov
authors.affiliation: Institute of Macromolecular Chemistry , AS CR, Heyrovsky Sq. 2, Prague, Prague 6, 162 06, Czech Republic.
authors.forename: Nadiia
authors.initials: N
authors.lastname: Velychkivska
authors.affiliation: Institute of Macromolecular Chemistry , AS CR, Heyrovsky Sq. 2, Prague, Prague 6, 162 06, Czech Republic.
authors.forename: Larisa
authors.initials: L
authors.lastname: Starovoytova
authors.affiliation: Institute of Macromolecular Chemistry , AS CR, Heyrovsky Sq. 2, Prague, Prague 6, 162 06, Czech Republic.
authors.forename: Zulfiya
authors.initials: Z
authors.lastname: Cernochova
authors.affiliation: ISIS-STFC, Rutherford Appleton Laboratory, Chilton, OX11 0QX Oxon United Kingdom.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Rogers
authors.affiliation: School of Pharmacy, University of Reading, Whiteknights , PO Box 224, Reading, RG6 6AD Berkshire, United Kingdom.
authors.forename: Wing Man
authors.initials: WM
authors.lastname: Lau
authors.affiliation: School of Pharmacy, University of Reading, Whiteknights , PO Box 224, Reading, RG6 6AD Berkshire, United Kingdom.
authors.forename: Vitaliy V
authors.initials: VV
authors.lastname: Khutoryanskiy
authors.affiliation: Department of Pharmacy & Research Centre in Topical Drug Delivery and Toxicology, University of Hertfordshire , Hatfield, AL10 9AB Hertfordshire, United Kingdom.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Cook