Chemistry Reference
In-Depth Information
Table 3.
Activation energies for gas permeation and diffusion for two composite films
Gas
CO
2
O
2
N
2
CH
4
E
P
(kJ/mol)
PI/20 wt% PS
8.95
15.44
20.48
18.49
PI/20 wt% PSVP
8.59
14.01
7.82
9.12
E
D
(kJ/mol)
PI/20 wt% PS
31.8
40.1
46.6
34.2
PI/20 wt% PSVP
32.5
45.0
54.1
36.4
P
0
PI/20 wt% PS
224.7
556.1
1143.7
552.2
PI/20 wt% PSVP
75.7
179.1
8.1
15.2
D
0
PI/20 wt% PS
2.0
×
10
-3
4.2
×
10
-3
0.244
1.1
PI/20 wt% PSVP
6.3
×
10
-4
0.403
8.7
3.7
×
10
-3
E
P
: activation energy for gas permeation
E
D
: activation energy for gas diffusion
P
0
and D
0
: the pre-exponential factors of Arrhenius expressions
P = P
0
exp(-E
P
/RT) (4)
D = D
0
exp(-E
d
/RT) (5)
where P
0
and D
0
are pre-exponential factors, E
p
is the apparent activation energy
for permeation, E
d
the activation energy for diffusion, R the gas constant, and T is
the temperature. It was found that the temperature dependence of P and D for the
two composite films could be described by the Arrhenius equations, too. There-
fore, activation energies for the gas transport could be obtained and are summa-
rized in Table 3.
3.3. Preparation and characterization of PI nanofoams
Both the PSVP and PS-based nanospheres in the nanocomposite films were ther-
molysized at 380°C for 2 hrs. The TEM micrographs and the properties of foams
prepared through this process are shown in Figures 9, 10 and Tables 4, 5, respec-
tively. The porous structure of the foams is obvious with the white areas repre-
senting voids from the PS nanospheres. Comparing with those of the PI nano-
composite, the TEM micrographs showed pores sizes ranging from 30 nm to 100
nm with some interconnections. The larger pore size and the interconnections
were mainly due to the agglomeration of the nanospheres in the composite films
and partially to the plasticization accompanying the “blowing” effect on the PI at
high temperature [27]. It can be seen from Tables 4 and 5 that the volume fraction
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