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Probing the Morphology and Nanoscale Mechanics of Single Poly( N ‐isopropylacrylamide) Microgels Across the Lower‐Critical‐Solution Temperature by Atomic Force Microscopy
Author(s) -
Tagit Oya,
Tomczak Nikodem,
Vancso G. Julius
Publication year - 2008
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.200700260
Subject(s) - poly(n isopropylacrylamide) , materials science , nanoscopic scale , spheres , particle (ecology) , lower critical solution temperature , atomic force microscopy , morphology (biology) , elastic modulus , composite material , indentation , nanotechnology , chemical physics , copolymer , polymer , chemistry , astronomy , geology , biology , genetics , oceanography , physics
Submicrometer‐sized particles of poly(N‐isopropylacrylamide) (PNIPAM) are synthesized by surfactant‐free radical polymerization. The morphology and nanomechanical properties of individual, isolated PNIPAM microgel particles at the silicon/air and silicon/water interfaces, below and above the PNIPAM volume‐phase‐transition temperature (VPTT), are probed by atomic force microscopy. In air, and in water below the VPTT, the PNIPAM spheres are flattened and adopt a pancakelike shape. Interestingly, above the VPTT the microgels adopt a more spherical form with increased height and decreased width, which is attributed to reduced interactions of the particles with the substrate. The elastic modulus calculated from force‐indentation curves obtained for individual microgel spheres reveals that the stiffness of the particle’s surface decreases by two orders of magnitude upon swelling in water. Additionally, the modulus of the PNIPAM spheres in water increases by one order of magnitude when crossing the VPTT from the swollen to the collapsed states, indicating a more compact chain packing at the particle surface.