Poly(1-trimethylsilyl-1-propyne) (PTMSP) has garnered significant research interest as the most permeable poymer yet discovered. This extremely high permeability is most apparent in the transport of organic vapors, where sorption of the gas in the polymer plays a dominant role. Morphologically, PTMSP exhibits very high free volume and therefor exhibits poor size selectivity with regards to diffusion dominated permanent gases. This combination of high sorption selectivity and low diffusive selectivity leads to reverse selective separations and has prompted consideration for a number of industrial processes where it is desirable to remove a larger species from a mixed gas while maintaining pressurization of the smaller species.

To date, all investigations of PTMSP have relied on bulk measurements of permeability, while generally ignoring local heterogeneities. Here, we invoke Flux Lateral Force Microscopy (F-LFM), to explore local gas flux in PTMSP. By rastering a scanning probe microscope (SPM) and observing the lateral deflection of the cantilever, it is possible to determine local friction at the polymer surface. Much like an air hockey table, when the substrate is exposed to a gas stream, a corresponding decrease in friction is observed. In addition to providing local flux information, the technique is unique in that it provides access to both diffusive and rheological behaviors, allowing study of their coupled influence on polymer transport.

While suitable for the study of bulk homogoneous polymers, the technique is most valuable in the study of heterogenous or anisotropic membranes whose permeability varies spatially on micron and nanometer length scales. To this end, we have studied the presence of silica interfaces in PTMSP, which have been shown to significantly improve permeability and selectivity of the membrane, particularly when the interfaces originate from high surface area to volume nanoparticles. This enhancement is unique given that traditional Maxwell type models suggest that permeability should decrease volumetrically with the addition of an impermeable phase. Here, flux in the vicinity (~100nm) of the nanoparticles has been explored and compared to the bulk to determine the extent of the interfacial modification.