Blends of two polymers,
poly(ethene-co-styrene) (PES) and
poly(2,6-dimethyl-1,4-phenylene oxide) (PPO),
were examined with tapping mode atomic force microscopy (AFM) using
various values of the driving
amplitude A
0 and set-point amplitude ratio
r
sp =
A
sp/A
0, where
A
sp is the set-point amplitude. In
height
and phase images of PPO/PES blend samples, the relative contrast of
chemically different regions depends
sensitively on the r
sp and
A
0 values. As the tip−sample force is
increased from small to large, both phase
and height images of PPO/PES blend samples can undergo a contrast
reversal twice. This makes it
difficult to assign the features of height and phase images to
different chemical components without
performing additional experiments. Phase and height images were
interpreted by analyzing several factors
that affect the dependence of phase shift and amplitude damping on
r
sp and A
0.
Tapping mode atomic force microscopy (TMAFM) measurements were performed for blends of two
elastomers, cis-1,4-butadiene rubber (BR) and styrene-co-butadiene rubber (SBR) containing silica filler
particles. To help interpret the TMAFM phase and height images of the BR/SBR blends, transmission
electron microscopy (TEM) measurements were carried out for the BR/SBR blends, and dynamic mechanical
analysis (DMA) as well as frequency-sweep/force-probe TMAFM measurements were carried out for BR
and SBR homopolymers. TEM images show that silica filler particles of BR/SBR blends are present mainly
in the SBR component, and DMA results reveal that BR has a lower glass transition temperature than
does SBR. In the phase images of BR/SBR blends the less stiff component BR is brighter than is the stiffer
component SBR. For the rational interpretation of TMAFM phase images of viscoelastic materials, it is
crucial to consider the indentation depth of the tip into samples as well as the reduced tip−sample energy
dissipation, not the total tip−sample energy dissipation. At a given set-point ratio the indentation depth
is smaller on the stiffer component SBR than on the less stiff component BR, but at a given indentation
depth the phase shift is larger on the stiffer component SBR. The phase shift increases almost linearly
with increasing the reduced tip−sample energy dissipation. The reduced tip−sample sample energy
dissipation is larger for SBR than for BR in agreement with DMA results.
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