(6ab) Understanding of Polymers in Confined Thin Films and Bulk Membranes: Fluorescence Based Approach

My research interest is to develop core understanding of material properties of functional polymers in thin film and bulk membrane format using fluorescence and other complementary surface characterization techniques (spectroscopic ellipsometry, quartz crystal microbalance, neutron reflectometry).

Bulk membranes have potential applications in bioseparation, water purification, fuel cell applications and so on. Virus filtration membranes work based on size exclusion mechanism and are used to remove viral contaminants during the processing and commercial production of therapeutic proteins. The biggest challenge in these processes is lack of sufficient understanding of virus retention mechanism. This knowledge is pivotal to understand the trends in flux and log reduction values (LRVs) of virus filtration membranes with increased volumetric throughput. The application of fluorescence confocal microscope to visualize the virus retention zones along the thickness of the membranes is a very exciting and new concept. This has been taken one step forward by adopting a multiple dye approach to track model bacteriophage retained inside virus filtration membranes (DV20, Vireolsve pro and Viresolve NFP) at different stages of membrane operations with intermittent pressure releases (Post-doc at ChE, Penn State, PI: Prof. Andrew Zydney). Fluorescence based techniques offer unique opportunities to distinguish between virus captured before and after process interruptions. This, in turn, gives interesting insights about the effect of pore structure and morphology on virus retention.

Fluorescence, when used in conjunction with other surface characterization techniques, provides a powerful platform to characterize transport properties and mobility of polymer and water in bulk polymer membranes as well as thin films. Bulk free-standing and confined supported systems behave very differently at hydrated state in terms of material properties. When the film thickness approaches to several tens of nanometers, the optical, mechanical and transport properties are dominantly controlled by the interfaces. The mobility of the polymer chains is constrained due to severe confinement effect. 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 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 based techniques can overcome many of these issues. Fluorescent probes sensitive to local viscosity and proton concentration were incorporated into ionomer thin films and membranes and the changes in fluorescence properties of the dyes as a function of film thickness and hydration were studied (Post-doc at MatSE, Penn State, PI: Prof. Michael Hickner). The changes in fluorescence offered valuable insight into stiffness and proton mobility of hydrated bulk and confined systems. The work clearly demonstrated the differences between confined and bulk systems. The study has prime importance in nanoscale understanding and advanced level designing of polymer-catalyst interface in fuel cells.

In addition, fluorescent p-conjugated oligoelectrolytes were synthesized and characterized in solution and solid state utilizing their light-harvesting properties. This was a part of my PhD work. Layer-by-layer self-assembled thin films of fluorescent oligoelectrolytes were investigated to develop fluorescence based bioassay platforms.

The multi-disciplinary work experience enabled me to innovate effective techniques to understand functional materials more deeply for a range of applications. As a future faculty, I would like to perform independent as well as collaborative research focusing on structure-property relationships and material development for (1) energy applications and (2) chemobiosensing. The application of fluorescence based techniques in fuel cell research is quite new, has already started offering interesting insights and has a lot of scope of work. An array of confined and bulk ionomeric systems will be probed using fluorescent functional sensory molecules and water-polymer-substrate interaction will be further explored. Other surface characterization techniques can help to validate the hypothesis from fluorescence based analysis and strengthen the arguments about unknown scenerios in confined systems. This will solve a lot of mysteries hidden inside these geometries. Techniques will be developed to probe zone-specific density, water/proton transport and mobility. This will be of specific interest and the knowledge earned from materials studies will be employed to develop new materials with desired hydration and transport properties. The study will be extended to light harvesting molecules in confined systems with varied geometry and microenvironment. Typical light induced energy and charge transfer phenomena will be tuned for better and cheaper solid state biodetection platforms with improved sensitivity and selectivity.