This work aims to systematically investigate the gas transport behavior in two glassy polymers.
One is the rigid, high fractional free volume (FFV) poly(1-trimethylsilyl-1-propyne) [PTMSP], and the other is
the relatively flexible, considerably lower FFV ethylcellulose (EC). Both polymer systems are filled with a series
of various molecular weight (M
w) trimethylsilylsaccharides [TMSS] (trimethylsilylglucose (M
w = 180) [TMSG],
trimethylsilyldextran1 (M
w = 900−1200) [TMSD1], and trimethylsilyldextran500 (M
w = 350K−550K)
[TMSD500]). The consistent trend of decreasing gas permeability, diffusivity, and solubility with increasing
load of the TMSS fillers was observed in the PTMSP/TMSS system. In addition, the extent of reduction of gas
permeability, diffusivity, and solubility in these composites is closely related to the M
w of TMSS fillers at an
equivalent load of various TMSS in the PTMSP matrix. For example, the PTMSP permeability to nitrogen reduced
227-fold, 43-fold, and 4-fold when filled with constant 27.2% TMSG, TMSD1, and TMSD500, respectively.
The diffusivity decreased 45-fold, 21-fold, and 3-fold, and the solubility decreased 5.0-fold, 2.0-fold, and 1.3-fold, respectively. The decreases in permeability, diffusivity, and solubility are directly related to the decrease of
FFV in PTMSP caused by the incorporation of the various M
w fillers. In contrast to the decrease of permeability
observed in the PTMSP/TMSS system, a systematic increase of gas permeability and diffusivity was obtained
for the EC/TMSS system with increasing load of TMSS fillers. However, no consistent change of solubility was
observed in EC/TMSS. Moreover, the gas diffusivity increase for the EC/TMSS system correlated well with the
M
w of the TMSS fillers, in contrast to the permeability increase. For example, when TMSG, TMSD1, and TMSD500
were used as fillers, the permeability to nitrogen of EC composites with 32.1% fillers increased 1.75-fold, 1.81-fold, and 1.64-fold, respectively, compared to that in unfilled EC. The diffusivity increased 3.32-fold, 1.84-fold,
and 1.31-fold, and the solubility increased −1.87-fold, 0-fold, and 1.25-fold, respectively. All applied TMSS
fillers led to an increase of gas diffusivity, which can be attributed to an increased chain mobility. The chain
mobility changes in EC/TMSS resulted in changes of the excess FFV of EC and therefore altered the gas solubility.
The increase extent of chain mobility was the highest with the lowest M
w TMSS.
