Probing the Morphology and Nanoscale Mechanics of Single Poly(N-isopropylacrylamide) Microgels Across the Lower-Critical-Solution Temperature by Atomic Force Microscopy

O. Tagit, N. Tomczak, Gyula J. Vancso

Research output: Contribution to journalArticleAcademicpeer-review

62 Citations (Scopus)

Abstract

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 particles 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.
Original languageUndefined
Pages (from-to)119-126
Number of pages8
JournalSmall
Volume4
Issue number1
DOIs
Publication statusPublished - 2008

Keywords

  • IR-71159
  • METIS-247986
  • Atomic Force Microscopy
  • nanoindentation
  • elastic modulus
  • microgels

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