Chemistry Reference
In-Depth Information
of gas absorbed by the polymer after completion of the successive transfers is
given by (
3
):
p
ðkÞ
f
V
ðkÞ
pol
D
M
g
R
m
ðÞ
D
sol
¼
Z
ðkÞ
f
T
ðkÞ
f
2
4
3
5
;
(3)
p
ðk
1
Þ
f
V
k
1
ð
Þ
V
2
V
p
D
p
ðkÞ
i
p
ðkÞ
f
V
2
þ
V
3
V
pol
M
g
R
V
3
pol
þ
þ
Z
ðÞ
i
T
ðÞ
i
Z
k
1
ð
Þ
T
k
1
ð
Þ
Z
ðÞ
f
T
ðÞ
f
f
f
m
ðÞ
sol
where
D
is the increment in dissolved gas mass resulting from the transfer
V
ðkÞ
pol
k
, and
D
is the change in volume after transfer
k
.
2.2 pVT-Calorimetry: Scanning Transitiometry
Certainly, calorimetry is a major technique for measurement of the thermodynamic
properties of substances and for following phase change phenomena. In most
applications, calorimetry is carried out at constant pressure, while the tracked
phenomenon is observed with increasing or decreasing temperature. The possibility
of controlling the three most important thermodynamic variables (
p
,
V
, and
T
)
during calorimetric measurements makes it possible to perform simultaneous
measurements of both thermal and mechanical contributions to the thermodynamic
potential changes caused by the perturbation. Calorimetric techniques provide
valuable additional information on transitions in complex systems. Their contribu-
tion to the total change of thermodynamic potential not only leads to the complete
thermodynamic description of the system under study, but also permits the investi-
gation of systems with limited stability or systems with irreversible transitions. By a
proper external change of the controlling variable, the course of a transition under
investigation can be accelerated, impeded, or even stopped at any degree of its
advancement and then taken back to the beginning, all with simultaneous recording
of the heat and mechanical variable variations. The seminal presentation by Rand-
zio [
20
] of thermodynamic fundamentals for the use of state variables
p
,
V
, and
T
in
scanning calorimetric measurements opened the path [
21 23
] from
pVT
calorime-
try to the now well-established technique of scanning transitiometry [
24
,
25
]. The
main characteristics of scanning transitiometry are reviewed in this section.
Practically, the technique utilizes the principle of differential heat flux calorim-
etry, with which it is possible to operate under four thermodynamic situations
where the perfectly controlled variation (or perturbation) of one of the three state
variables (
p
,
V
,or
T
) is simultaneously recorded with the thermal effect resulting
from the generated perturbation of the system under investigation. The principle of
scanning transitiometry [
23
] offers the possibility to scan, in the measuring calori-
metric cell, one of the three independent thermodynamic variables (
p
,
V
,or
T
)
