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Stimuli‐Responsive, Shape‐Transforming Nanostructured Particles
Author(s) -
Lee Junhyuk,
Ku Kang Hee,
Kim Mingoo,
Shin Jae Man,
Han Junghun,
Park Chan Ho,
Yi GiRa,
Jang Se Gyu,
Kim Bumjoon J.
Publication year - 2017
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.201700608
Subject(s) - lower critical solution temperature , materials science , polymer , poly(n isopropylacrylamide) , chemical engineering , pulmonary surfactant , polystyrene , particle (ecology) , micelle , dissolution , smart polymer , copolymer , nanotechnology , aqueous solution , composite material , organic chemistry , oceanography , chemistry , engineering , geology
Development of particles that change shape in response to external stimuli has been a long‐thought goal for producing bioinspired, smart materials. Herein, the temperature‐driven transformation of the shape and morphology of polymer particles composed of polystyrene‐ b ‐poly(4‐vinylpyridine) (PS‐ b ‐P4VP) block copolymers (BCPs) and temperature‐responsive poly( N ‐isopropylacrylamide) (PNIPAM) surfactants is reported. PNIPAM acts as a temperature‐responsive surfactant with two important roles. First, PNIPAM stabilizes oil‐in‐water droplets as a P4VP‐selective surfactant, creating a nearly neutral interface between the PS and P4VP domains together with cetyltrimethylammonium bromide, a PS‐selective surfactant, to form anisotropic PS‐ b ‐P4VP particles (i.e., convex lenses and ellipsoids). More importantly, the temperature‐directed positioning of PNIPAM depending on its solubility determines the overall particle shape. Ellipsoidal particles are produced above the critical temperature, whereas convex lens‐shaped particles are obtained below the critical temperature. Interestingly, given that the temperature at which particle shape change occurs depends solely on the lower critical solution temperature (LCST) of the polymer surfactants, facile tuning of the transition temperature is realized by employing other PNIPAM derivatives with different LCSTs. Furthermore, reversible transformations between different shapes of PS‐ b ‐P4VP particles are successfully demonstrated using a solvent‐adsorption annealing with chloroform, suggesting great promise of these particles for sensing, smart coating, and drug delivery applications.