AmericanChemicalSociety.com

The performance of organic-inorganic composite membranes (or mixed matrix membranes) is greatly influenced by the nature and structure of the interfaces between the two dissimilar phases. Thus it is important to understand the interaction between the organic and inorganic phases at their interface, ultimately enabling design of the interface to fully realize the potential for dramatically improved membrane performance by using highly selective phases in a polymer matrix. It has, however, proven very difficult to examine the interfacial region in these membranes in part because of their small volume and also because of the limitations of conventional characterization techniques. This two-year new investigator project focuses on developing model systems and applying non-destructive techniques, fluorescence spectroscopy and Raman spectroscopy, to gain a quantitative understanding of the structure and properties of these interfaces. The working hypotheses of the proposed work are: 1) the interfaces between micro-/meso-porous metal oxide and polymer phases (in mixed matrix membranes) are very different from those between non-porous oxides and polymer phases and 2) the interfacial structures can be controlled by the surface chemistry as well as the surface nanostructures of metal oxides and the polymer chemistry.

The first objective is to develop two dimensional model systems of micro-/meso-porous oxides with tunable surface chemistry and surface nanostructures, and to determine the structures of polymers in the interfacial regions using fluorescence and Raman spectroscopies. Understanding the interfacial structures of polymers with micro-/meso-porous metal oxides provides a fundamental basis to intelligently tune and rationally design the interfaces to successfully realize the full promise of mixed matrix membranes.

The second objective is to study the effects of the surface chemistry of the metal oxides as well as their surface nanostructures on the interfacial structures. For maximum performance enhancement, the glass transition temperature (Tg) shift and the thickness of polymer in the interfacial regions is to be minimized while maintaining good adhesion between polymer and oxide surface.

The work that has so far been conducted as part of this grant makes two contributions to achieve these objectives: (1) develop two-dimensional model systems, and (2) construct a custom-made sample state with temperature control and incorporate into a fluorescence spectrometer

The first objective of this work has dealt with developing new methods. The methods include the extended “micro-tiles-and-mortar-joint method” and “thermal seeding method”. With these novel methods that have been developed in our group, we were able to prepare model films of porous materials such zeolites and metal-organic frameworks. A part of this portion of the work has been conducted by Inho Lee and Victor Varela. Inho Lee obtained his PhD and now works at Dow Chemical. Victor Varela is a PhD student. One journal paper has been published, another manuscript submitted, and the third in preparation. Three conference presentation have been made.

The second objective of the conducted work was to build a custom-made sample stage and integrate into a fluorescence spectrometer.  A fluorescence spectrometer was purchased. The stages are currently being tested. This portion of the work has been conducted by Gil-Pyo Kim who was a PhD student in the group. However, Gil-Pyo left the group after he failed in qualifying exam. Currently I am looking for a new graduate student.

In summary, the grant PRF# 48884-DNI5 partially supported three PhD students and resulted in three journal papers and 3 conference papers that acknowledge ACS-PRF support.