Chemistry Reference
In-Depth Information
the PVDF polymerization, it is essential to document the thermodynamics of the
{C
2
H
2
F
2
-PVDF} system to better control the polymerization industrial process.
Melting/crystallization under high pressure (i.e., supercritical) C
2
H
2
F
2
has been
investigated through isobaric temperature scans on PVDF samples (
M
n
¼
113.100
10
3
gmol
1
and
M
w
¼
10
3
gmol
1
, respectively) at different pressures
between 0.1 and 180 MPa [
55
]. Isobaric temperature scans on PVDF samples under
high pressure N
2
have been performed between 0.1 and 30 MPa.
This study shows, like in the case of the {MDPE-CH
4
} system, the significant
influence of the “active” supercritical solvent on the melting/crystallization of the
polymer. Figure
15
shows the influence of supercritical C
2
H
2
F
2
and of supercritical
N
2
on the
T
m
and
T
cr
of PVDF. Obviously, both temperatures increase with
increasing N
2
pressure. In the investigated pressure range (0.1 30 MPa), the
(Clapeyron) slope of the two plots
T
m
/
p
and
T
cr
/
p
were 0.108
0.002 K MPa
330.000
1
0.002 K MPa
1
, respectively. By contrast, C
2
H
2
F
2
depresses first the
melting/crystallization temperatures upon sorption of the gas by the polymer, up to
30 MPa. Then, the antiplasticization effect of the hydrostatic pressure of C
2
H
2
F
2
takes over above 30 MPa, which confirms the usual competition between plastici-
zation and hydrostatic effects of a (chemically) “active” SCF on the melting/
crystallization phenomena: the hydrostatic pressure increases the temperature of
the first-order transitions, while the increase of solubility of the SCF in the polymer-
rich phase depresses this temperature.
and 0.115
3.4.2
Isotropic Transitions (Self-Assembling of Polymeric Structures
Under High-Pressure Gas Sorption)
Different fields of application require the knowledge of interfacial phase behavior
between gaseous molecules and polymers. New application fields appear with the
rapid growth of information technology, for which ongoing downscaling of micro-
electronics evolves into nanoelectronics. The development of highly ordered
Fig. 15 Pressure temperature phase diagram for the two systems {C
2
H
2
F
2
PVDF} (
open sym
bols
) and {N
2
PVDF} (
closed symbols
) showing the depression by about 20 K of melting
temperature (
right
) and crystallization temperature (
left
) at pressures up to 30 MPa for PVDF
under supercritical C
2
H
2
F
2
