Paper NS-ThM3
In Situ Nanoscale Characterization of Gas Fluxes of Organic Membranes by Flux-Lateral Force Microscopy

Thursday, November 12, 2009, 8:40 am, Room L

Characterization studies of polymeric membranes for enhancing the gas transport rates are highly significant in current separation technologies. However transport property analyses like gas permeability measurements are bulk scale methods with limited access to local transport properties in multiphase systems such as nanocomposites membranes. In this context our group has developed a flux-lateral force microscopy (F-LFM) technique¹ for the in situ nanoscale characterization of the membranes, by monitoring the gas fluxes through them on a nanoscale. This technique, which is based on atomic force microscopy (AFM) utilizes the lubricating effect and the mechanical property changes in the membrane to determine fluxes. It was demonstrated by this technique that lateral force vs. pressure curves offered a direct measure of local gas permeabilities. In this paper we present the nanoflux analysis in Poly(trimethyl silyl propyne) (PTMSP), a glassy polymer with highest gas permeability of all known synthetic polymeric systems as well as high organic vapor/permanent-gas selectivity. The local fluxes in PTMSP films measured by F-LFM are compared to global fluxes obtained from conventional integrated methods. The sensitivity of F-LFM technique is demonstrated by presenting the reverse selective transport rates of He and CO₂ in PTMSP membranes as detected by the technique. The paper will also address the impact of aging, and flux dependence on film thickness.

Reference:

¹ J.H. Wei, M. He, and R.M. Overney, Direct measurement of Nanofluxes and Structural Relaxations of Perflourinated Ionomer Membranes by Scanning Probe Microscopy, J.Membrane Sci. 279, 608-14 (2006)