Concept for proposal to NIST

I am planning to write  a proposal to the NIST Measurement Science and Engineering (MSE) Research Grant Program. Federal Funding Opportunity (FFO) is here.

The proposal is due in the beginning of June.  From talking with a friend at RIT would has one of these presently, it sounds like the best strategy is to target an initial 1 year project w/ a budget of <$100k.  It is reasonably easy to get renewals for up to 3-5 yrs total.  Below is an abstract of the initial idea I have to study gas transport through ultra-thin (e.g. <10 nm) polymer films that are supported on the pnc-Si membrane.  I am listing a couple potential other areas of study with this concept for future years at the end of the abstract.  If anyone has comments or thoughts on other interesting avenues of study with this please let me know.

Working Title: Novel method using ultra-thin nanoporous membranes for measuring gas permeation through nanometer-scale polymer films

Abstract: We have developed an ultrathin, nanoporous membrane platform that can enable transport measurements such as gas permeation through polymer films with thicknesses on the order of 10 nm or less.  This membrane platform is based on standard silicon processing techniques to create porous, nanoncrystalline silicon (pnc-Si) membranes on a thickness scale of ~15 nm with controllable pore sizes in the range of 5 to 25 nm, and this has been successfully applied to size-based molecular separations.  We now wish to use this technology to support ultrathin polymer films for use in gas permeation measurements.

An initial important application that we propose pursuing is to measure oxygen permeation through proton-conducting ionomer (perfluorosulfonic acid, PFSA) films, which is of relevance in understanding and optimizing the performance of electrodes in proton exchange membrane fuel cell (PEMFC) applications.  These electrodes are commonly comprised of platinum supported on carbon particles that that have an ultrathin (~2 nm) coating of ionomer.  Recent studies of the performance of fuel cell electrodes have indicated that the resistance of oxygen permeation through the ionomer film is significant, especially for very low catalyst loadings.  The issue with existing data is that the permeation rate can only be inferred from rather complex electrochemical tests or permeation tests of ionomer films on the order of 10’s of microns.  The film thickness in electrodes is orders of magnitude lower, and the permeation properties may very well change as the length scale of the ionomer film shrinks to the nanometer scale – near that of the polymer chain’s length scale.  Indeed, some recent studies using microelectrode techniques with ionomer films down to ~200 nm thicknesses have shown that the permeation does drop significantly at film thicknesses less than about one micron.

Using our pnc-Si membrane as a substrate, we believe it will be possible to create ionomer films at the scale of 10 nm thick through spin coating of dilute ionomer solution.  These can then be used to make straightforward permeation measurements owing to the porous nature of the pnc-Si membrane.  The advantage of our membrane for this application are that it offers a nealry atomically smooth surface to enable fabrication of high fidelity polymer films, even at the 10 nm thickness scale.  Additionally, the surface of the pnc-Si membrane can be readily functionalized to adjust the surface energy, which provides further flexibility in creating polymeric film coatings on the surface of the membrane.   An additional important feature of this proposed measurement system is that it is robust to heating and exposure to water vapor, which enables permeation measurements at conditions that are relevant to operating PEMFC systems.

Beyond this initial application to oxygen permeability we envisage several other important areas of exploration including:

• Measuring the ionic conductivity through films of this length scale.  As in the case of oxygen permeability showing a significant drop at thicknesses lower than about 1 micron, a recent study of proton conductivity has shown that this property is as much as an order of magnitude lower for films less than 100 nm compared to that of the bulk ionomer.
• Measuring oxygen permeability through corrosion inhibition films.
• Permeation of therapeutic drugs through ultrathin polymer films