Chemistry Reference
In-Depth Information
The foaming materials industry is a rapidly growing area where constant inno-
vation and added-value products are key factors for economic success in the face of
high international competition. The mastering of polymer degradation (typically
blistering) by high pressure dissolved gases is another key issue. Microelectronics
is presently the most competitive industrial activity. The focus of the present article
is thus on the behavior of {gas polymer} systems from the point of view of gas
solubility and associated thermal effects. Depending on the temperature and pres-
sure ranges, polymers are either in the solid or molten state, i.e., at temperatures
between
T
g
and the temperature of melting,
T
m
; in most cases, gases are supercriti-
cal fluids (SCFs). The present contribution, essentially based on current activities of
the authors, is split into two main parts: experimental measurements (Sect. 2) and
evaluation of gas-polymer interactions (Sect. 3) through experimental measure-
ments of gas solubility (Sect. 3.1), thermal effects reflecting interaction energies
(3.2), thermophysical properties of polymers (3.3) and phase transitions (3.4).
In addition, the importance of such data for engineering applications is stressed.
This article illustrates the contribution of two techniques in providing accurate
information to meet the demand for the data described above: the vibrating-wire
(VW) pressure-volume-temperature (
pVT
) technique for gas sorption and polymer
swelling; and scanning transitiometry for simultaneous thermal and mechanical
measurements. Two complementary thermodynamic approaches have been devel-
oped to characterize gas polymer interactions in evaluating either gravimetric and
volumetric changes or thermally energetic changes associated with gas sorption (up
to saturation) in a polymer. The first approach is based on a “weighing technique”
using a VW sensor coupled with a
pVT
method. The second approach is based on
the coupling of a calorimetric detector with a
p
,
V
,or
T
scanning technique.
2 Experimental Techniques
2.1 Gas Sorption and Solubility
Gas solubility in polymers can be measured using different techniques, i.e.,
gravimetric techniques, including vibrating or oscillating techniques;
pVT
techni-
ques with the pressure decay method; and gas-flow techniques. A brief review of
existing techniques is given below, followed by the description of a technique we
recently developed that couples a new gravimetric technique with a
pVT
pressure
decay technique.
2.1.1 Gravimetric Techniques
These techniques consist in precisely weighing a polymer sample during gas
sorption. They are very sensitive at low-to-moderate gas pressures [
5
,
6
], and use
