Chemistry Reference
In-Depth Information
a
b
30
transitiometer
cryostat
10
−
10
−
30
−
50
10
−
70
0
0
3600
7200
10800 14400
−
10
−
−
0.5
−
20
−
30
−
40
−
50
−
60
1.5
Transition
−
2.5
3.5
−
0
3600
7200
10800
14400
Time [s]
Temperature[°C]
Fig. 21 Scanning transitiometry technique for the investigation of polymer
T
g
at low temperature
and high pressure. (a) Experimental thermogram recorded during an isobaric temperature scan
under 50 MPa (on a styrene butadiene rubber sample of 1.56 g; scanning rate 0.666 mK s
1
). The
inset
shows the temperature programs for the transitiometer (
solid line
) and for the cryostat
(
dashed line
). (b) Typical thermograms (heat flux vs temperature) for the transition domain of
the vulcanized rubber are shown for different pressures. The
inset
shows the change of
T
g
with
pressure, and the slope gives the pressure coefficient
D
T
g
/
D
p
0,035
10 MPa
70 MPa
90 MPa
0,030
0,025
0,020
0,015
0,010
0,005
0,000
−
0,005
−
60
−
55
−
50
−
45
Temperature [
−
40
−
35
−
30
−
25
−
20
°
C]
Fig. 22 Effect of pressure on the
T
g
of vulcanized rubber under isobaric conditions. Typical
volume variations (
DV
vs
T
) are shown for the transition domain at 10, 70, and 90 MPa; the
scanning conditions are the same as used for the measurements reported in Fig.
21
It should be noted that
T
g
is expressed as the temperature corresponding to the
peak of the first derivative of the heat flux (i.e., at the inflexion point of the heat
flux). The volume variations associated with the glass transition, which are also
simultaneously measured by scanning transitiometric measurements, are depicted
in Fig.
22
. In accordance with the heat flux curve,
T
g
increases with increasing the
pressure. Above
T
g
, there is an increase of the slope of the variation of the specific
volume versus temperature. However, the change in the slope is gradual and
T
g
can
be determined at the point where the two lines intersect.
