RHEOLOGY OF CARBON BLACK SUSPENSIONS - Advances in Chemistry Research - page 33

frequency , and steady-state viscosity  as a function of shear rate  ． .Cone-plate

fixtures with a gap angle of 0.0845 rad and a plate diameter of 25 and/or 50 mm
were used. Prior to the measurements, the suspensions were sheared at a rate 10
s 1 for 2 min and then kept quiescently for 3 min. This pre-shear ensured a good
reproducibility of the data. After a quiescent rest for 3 min, the measured G and
G data did not change with time.
Transmission electron microscope (TEM) observation was performed for
solidified CB suspensions (for which the observation could be made in vacuum).
Fortunately, the CB/Varnish-1 and CB/Varnish-2 suspensions could be solidified by
a removal of a small amount of volatile components. After the solidification, the
specimens were microtomed to a ultrathin section of about 70 nm thickness using a
ultracryo-microtome with a diamond knife at 70C. The structure in the section
was observed under an electron microscope, JEM 100 (100 kV).
TEM was used to measure the particle size and the aggregate structure of CB.

The average aggregate diameter was measured with Microtrac UPA

(HONEYWELL).

3. Three Types of Dynamic Viscoelastic Behavior

In this section, the effects of the medium affinity to the CB particles on the
structure and rheology of the CB suspensions is elucidated. The CB sample
studied here have a relatively larger primary particle size and low oil absorption
value so that a rather small change in the affinity toward the CB particles can
results in large changes in the agglomerate structure and rheology [28].

3.1. Nonlinearity of Three Kinds of Suspensions

In the suspensions prepared as above, the CB concentration was varied from 0
to 20 wt% for CB/(PS/DBP) suspension and to 35 wt% for CB/Varnish-1 and
varnish-2 suspensions. The oscillatory strain amplitude  0 was varied over a wide
range, 0.1  0  500.For the CB-76/(PS/DBP) suspension with CB-76 concentration
c CB = 20 wt%, the CB-76/Varnish-1 suspension with c CB =30 wt%, and the
CB-76/Varnish-2 suspension with c CB =30 wt%, Figure 1 shows the dependence of
the apparent storage and loss moduli G app (a) and G app (b) at  = 1 rad s 1 on the
strain amplitude  0 .These moduli were measured from a single- strain sweep test,
and the pre-shear (for 2 min at 10 s 1 ) and successive quiescent rest (for 3 min) were
made prior to the test.