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Braun Group People

Nihan Yonet ,
Graduate Student in Materials Science and Engineering

BS degree from Fatih University (Turkey) in 2002

MS degree from Istanbul Technical University (Turkey) in 2004. Her major is in chemistry with polymer background.

 

Rachel Evans,
Former Graduate Student in Materials Science and Engineering (M.S. 7/07)

BS degree with honors from the University of Arizona in 2004 in Materials Science and Engineering.

Patterned Polymer Brushes for Directed Molecular Transport

The goal of our research is to produce well-defined patterned polymer brushes on silica surfaces to serve as pathways for molecular transport. Such patterned surfaces could be incorporated into lab-on-a-chip devices for chemical separations, molecular sensing and even cell communication. The patterned polymer brushes are formed by microcontact printing (μCP) a silane initiator followed by atom transfer radical polymerization, Figure 1. Two types of polymer brushes have been created: the thermoresponsive poly(n-isopropylacrylamide) (PNIPAAm) [1] that shows LCST behavior and the biologically relevant poly(oligo(ethyleneglycol)acrylate) (POEGA) [2]. The samples are characterized by ellipsometry, atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) to determine the thickness of the thin films, the quality of the patterning and the chemical composition of the polymers. It is critical that the polymer brushes be thick enough to incorporate molecules for transport and that the molecules be soluble in the brushes. It is also critical that there be a high degree of contrast between the polymer regions and the bare substrate regions so that the molecules stay within the brush pathways during transport. If there is even a slight layer of polymer outside of the brush regions, the transport molecules will stray and the device will fail. Ellipsometry, AFM and XPS give us exactly the information we need to design functional patterned polymer brush films.

            The transport of molecules in the patterned polymer brushes is studied using confocal laser scanning microscopy and fluorescence microscopy. Fluorescent molecules are used as the model diffusing species. Fluorescence recovery after photobleaching (FRAP) has been used to study the diffusion of Prodan in self-assembled monolayers [3] as well as solid-state PNIPAAm and POEGA brushes under various levels of humidity, Figure 2a. The transport of the fluorophore HPTS from a reservoir has been studied in patterned POEGA brushes as well [4], Figure 2b.

            Nihan’s research focuses on the chemical design and synthesis of varied polymer brushes while Rachel’s research focuses on the patterning and transport studies.

Figure 1.

Figure 2.

Acknowledgements

We would like to thank Dr. Carla Heitzman and Dr. Huilin Tu, former students in the Braun Group, for their years of creative research and hard work on the project. They laid a solid foundation for the successful work that we are now conducting.

 

References

1.         Huilin Tu, Carla E. Heitzman, Paul V. Braun. Patterned Poly(N-isopropyl-acrylamide) Brushes on Silica Surfaces by Microcontact Printing Followed by Surface Initiated Polymerization. Langmuir 2004, 18, 8313.

2.         Huilin Tu, Carla E. Heitzman, Rachel C. Evans, Paul V. Braun. Patterned Poly(oligoethylene glycol acrylate) Brushes on Silica Surfaces. Polymer Preprints 2005, 46, 444.

3.         Carla E. Heitzman, Huilin Tu, Paul V. Braun. Two-Dimensional Diffusion of Prodan on Self-Assembled Monolayers Studied by Fluorescence Recovery After Photobleaching.J. Phys. Chem B. 2004, 108, 13764.

4.         Rachel C. Evans, Huilin Tu, Nihan Yonet, Paul V. Braun. Directed Molecular Transport in Patterned Polymer Brushes. In preparation.

 

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