posted on 2016-09-20, 17:49authored byMartin Dehnert, Eike-Christian Spitzner, Fabian Beckert, Christian Friedrich, Robert Magerle
We investigate the
surface and subsurface morphology of stearylamine-modified
graphene oxide sheets and polystyrene-grafted functionalized graphene
oxide sheets through atomic force microscopy (AFM) operated in multi-set
point intermittent contact (MUSIC) mode. This allows a depth-resolved
mapping of the nanomechanical properties of the top surface layer
of the functionalized graphene oxide sheets. On the surface of stearylamine-functionalized
graphene oxide sheets, we can distinguish areas of hydrophilic graphene
oxide from hydrophobic areas functionalized with stearylamine. We
find that every sheet of graphene oxide is functionalized with stearylamine
on both sides of the sheet. The exposure of polystyrene-grafted functionalized
graphene oxide to chloroform vapor during the AFM measurement causes
a selective swelling and a softening of the polystyrene envelope.
The depth-resolved mapping of the tip–sample interaction allows
the shape of the folded and wrinkled graphene oxide sheets within
the polystyrene envelope to be imaged; furthermore, it allows the
thickness of the swollen polystyrene envelope to be measured. This
yields the swelling degree, the grafting density, and the average
chain conformation of the grafted polystyrene chains, which we find
to be in the brush regime. Our work demonstrates a versatile methodology
for imaging and characterizing functionalized and polymer-grafted
two-dimensional materials on the nanometer scale.