Polyimide/polystyrene nanocomposite films as membranes for gas separation and precursors for polyimide nanofoams - Polyimides and Other High Temperature Polymers - page 475

seen from Figures 6a, 6b and 6c. The relatively homogeneous dispersion of the
PSVP nanospheres in the PI matrix might be due to the partial interaction of
pyridinyl groups on the surface of the particles with the carboxyl groups of the
PAA chains before the PAA was imidized. The surface pyridinyl groups are de-
tected from PSVP nanospheres by XPS (Figure 4). The interaction of tertiary
amine with carboxyl group and the formation of amine salt between them has
been successfully applied for the preparation of PI Langmuir-Blodgett films [17-
18]. Gas transport properties, such as gas diffusion coefficient, of the film might
reflect to a certain degree such interaction because the diffusion coefficient de-
pends strongly on the packing density of polymer chains in the film. Specific in-
teractions in the polymer film normally increase the packing density and decrease
the gas diffusion coefficient. Therefore, using the time-lag method, the gas trans-
port properties of these PI nanocomposite films were measured.

3.2. Pure gas separation properties of composite films filled with PS-based
nanospheres
Gas separation properties of these films for CO 2 , O 2 , N 2 and CH 4 gases at 35 C

and 10 atm are listed in Table 1. For comparison, the gas permeability data ob-
tained under the same conditions in our laboratory for the PMDA/ODA PI film
are also included. PIs have good mechanical and thermal properties together with
high gas permeabilities, which are greatly affected by the structure of PI mole-
cules; and widely varying gas permeability values are reported in the literatures
[19-23]. Hirayama et al. [19] have reported the permeabilities of 32 different PIs
and examined in detail the relation between gas permeabilities, diffusivities and
solubilities and the structures of various PIs. Recently, Alentiev and co-workers
[24] presented a novel approach for the prediction of gas transport parameters
(permeability and diffusion coefficients) of amorphous PIs. In contrast to the al-

°

Table 1.
Gas permeabilities (P) and permselectivities ( α ) of films at 35 ° C and 10 atm

Film P CO2 O2 P N2 P CH4

α CO2/N2 α CO2/CH4 α O2/N2

PI/10 wt% PS 2.33 0.55 0.085 0.049 27.4 47.5 6.47

PI/15 wt% PS 2.32 0.50 0.090 0.049 25.8 47.3 5.56

PI/20 wt% PS 2.90 1.34 0.91 0.34 3.19 8.53 1.45

PI/25 wt% PS 4.29 1.77 0.91 0.48 4.71 8.94 1.94

PI/10 wt% PSVP 3.58 0.82 0.13 0.10 28.4 35.8 6.31

PI/15 wt% PSVP 3.71 0.81 0.14 0.10 26.5 36.4 5.79

PI/20 wt% PSVP 5.65 0.91 0.15 0.14 38.4 41.2 6.07

PI/25 wt% PSVP 6.55 1.99 1.52 2.19 4.31 3.00 1.31

PI 2.00 0.40 0.063 0.024 31.7 83.3 5.00

P in Barrers