In Search of the Elusive Interphase
G.S. Blackman, K.J. Van Vliet, C.A. Tweedie, G. Constantinides
nanocomposite, nanoindentation, scanning probe microscopy, interphase
One of the hypotheses to explain the unique properties observed in polymer nanocomposites is that the inorganic particles influence or modify the polymer chains or molecules in the nearby vicinity. The effect has been observed in traditional composites where a thin skin surrounding the filler is somewhat different than the bulk polymer. As the size of the particles becomes smaller and the surface area of the inorganic phase becomes appreciable the so-called interphase can extend throughout the entire nanocomposite part and the interphase controls or dominates the performance. Direct chemical or mechanical evidence for this distinct polymer interphase is difficult to obtain. We present a systematic approach using nanoindentation and scanning probe microscopy to understand the nature and extent of the interphase in a polymer. We start by using the nanoindentor tip as a surrogate nanoparticle and measure the response of polymer molecules in the top 10’s of nanometers of the surface. We find that pure amorphous polymers show a general trend that the modulus increases near the top surface, due to rearrangement or reorganization of the polymer molecules. Further work with carefully controlled model nanocomposites materials will also be discussed.
Nanotech 2008 Conference Program Abstract