During the past few years, several novel
methods have been introduced in the field
of atomic force microscopy (AFM) to image
the mechanical properties of soft materials.
Tribological and viscoelastic properties have
been probed in friction force imaging under
sliding contact (1, 2) as well as cantilever-
modulation amplitude and/or phase imaging
under continuous (1-3) or intermittent
contact (4-6). On a viscoelastic material,
regions of greater loss modulus dampen the
cantilever modulation more substantially
(1-4), that is, dissipate more strain energy.
Enhanced viscoelastic dissipation also
translates into greater friction under sliding
contact (1, 2). Variations in storage modulus
and adhesion on a viscoelastic material
may further complicate frictional response.
A systematic examination of competing
mechanisms necessitates multiple,
complementary imaging modes.