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Viscoelastic Properties of Single Poly(ethylene glycol) Molecules
Author(s) -
Kawakami Masaru,
Byrne Katherine,
Khatri Bhavin S.,
McLeish Tom C. B.,
Smith D. Alastair
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200600116
Subject(s) - viscoelasticity , force spectroscopy , ethylene glycol , peg ratio , materials science , monomer , polymer , molecule , chemical physics , cantilever , creep , nanotechnology , atomic force microscopy , chemistry , composite material , organic chemistry , finance , economics
Abstract The viscoelastic properties of single poly(ethylene glycol) (PEG) molecules were measured by analysis of thermally and magnetically driven oscillations of an atomic force microscope (AFM) cantilever/molecule system. The molecular and monomer stiffness and friction of the PEG polymer were derived using a simple harmonic oscillator (SHO) model. Excellent agreement between the values of these two parameters obtained by the two approaches indicates the validity of the SHO model under the experimental regimes and the excellent reproducibility of the techniques. A sharp minimum in the monomeric friction is seen at around 180 pN applied force which we propose is due to a force induced change in the shape of the energy landscape describing the conformational transition of PEG from a helical to a planar state, which in turn affects the timescale of the transition and therefore modifies the measured internal friction. A knowledge of the viscoelastic response of PEG monomers is particularly important since PEG is widely used as a linker molecule for tethering groups of interest to the AFM tip in force spectroscopy experiments, and we show here that care must be exercised because of the force‐dependent viscoelastic properties of these linkers.