With a view to facing the not-so-far-away fossil fuel crisis, research focuses have been diverted towards sustainable energy based high efficiency energy conversion and storage devices. To achieve nation’s vision towards hydrogen economy, 2010-2040 is the timeframe during when DOE’s Energy Efficiency and Renewable Energy (EERE) program (FY16 budget $2.72B) plans the critical development of fuel cell and mass production of fuel cell based vehicles. The nanoscale understanding of polymer-catalyst interfaces on electrodes is crucial to lower the cost of fuel cell (target $30/KW) and improve the performance of sustainable energy propelled applications. Ionomer thin films behave very differently from bulk membranes at hydrated state due to severe confinement effect at interfaces. Although a great deal of work has been done so far to explore the material properties of ionomers in bulk membranes, the mobility, hydration and transport properties of functional ionomers in several nm-thick films are relatively unexplored. The challenges in characterizing thin films start when the conventional bulk characterization techniques fail to predict the nanoscale changes in materials properties. Fluorescence, when used in conjunction with other surface characterization techniques, overcome many of these issues and provides a powerful platform to characterize bulk membranes as well as thin films. Fluorescent probes sensitive to local viscosity, water-polymer mobility and proton concentration has been incorporated into ionomer thin films and membranes and the changes in fluorescence properties of the dyes as a function of film thickness and hydration has been studied. The changes in steady state and time-resolved fluorescence has offered valuable insight into stiffness and proton mobility of hydrated confined systems consistent with hydration behavior explored by QCM and Ellipsometry. In addition, the water-polymer and density distributions along the film thickness have been thoroughly investigated in hydrated thin polymer films using neutron reflectometry (Post-doc at MatSE, Penn State, PI: Michael Hickner).
Virus filtration membranes function predominantly through robust size exclusion mechanism and have potential applications in bioseparation and water purification. Current target is to achieve >4-log removal of virus particles from product streams with minimal membrane fouling and good capacity (>200 L/m2). The biggest challenges in removing viral contaminants from therapeutic drugs are lack of sufficient understanding of factors controlling virus retention within these membranes and unexpected decay in log reduction value (LRV) in course of filtration. Apart from the conventional quantitative studies of virus retention, the application of fluorescence confocal microscope enables the visualization of virus retention zones along the thickness of the membranes. This exciting and new concept has been taken one step forward by adopting a multiple dye approach to track model bacteriophage retained inside different virus filtration membranes (with varied pore structure and morphology) at different stages of membrane operations with intermittent pressure releases. Also the performance of these membranes has been improved by enabling dual mode virus capture (electrostatic adsorption and physical size based entrapping) (Post-doc at ChE, Penn State, PI: Andrew Zydney).
In addition, fluorescent p-conjugated oligoelectrolytes have been synthesized and characterized in solution and solid state utilizing their light-harvesting properties. Layer-by-layer self-assembled thin films of fluorescent oligoelectrolytes have been investigated to develop fluorescence based bioassay platforms (PhD at ChBE, National University of Singapore).
As a future faculty, I would like to address the critical concerns of unexplored confined systems and fill in the knowledge gaps in nanoscale polymeric and biomolecular systems utilizing my multi-disciplinary research experience. New and simpler techniques will be innovated to probe zone-specific material properties within thin film systems. A great emphasis will be given on synthesis of new molecules with varied geometry to improve confined state properties and develop next-generation materials for energy and biomedical applications.
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