TÜBİTAK 107T211 – Single Molecule Tracing in Confined Geometries (2007-2009)

Project final report in Turkish can be accessed from this link.

In this TÜBİTAK 1001 project, the motion of single terrylene molecules has been investigated in confined channels of an asymmetric diblock copolymer (poly(butadiene)-poly(ethylene oxide), PBPEO) by single molecule tracing. First, calibration measurements have been performed using single terrylene and Rhodamine B molecules stabilized in polymer thin films. In these measurements a piezoelectric translation stage was moved with 20-25 nm steps. The accuracy in determining the steps by using the single molecule images was shown to be ~1.5 nm. Sample preparation of the diblock copolymer thin films that involves spin coating and annealing has been optimized. One dimensional channel formation has been confirmed using atomic force microscope (AFM) phase images and scanning electron microscope (SEM) images.

One dimensional diffusion of single terrylene molecules in confined PB channels of PB-PEO diblock copolymer thin films were then observed by single molecule tracing. Parallel and curved channels observed in single molecule trajectories greatly resembled those observed in AFM and SEM images. Analyses perfomed on single molecule trajectories showed that the one-dimensional diffusion coefficients were significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients of terrylene molecules in PB. The trajectories of some single molecules also showed unusual behavior of directed motion where mean square displacement had a parabolic dependence on lag time. The likely origin of this behavior was the local variations in the PB channel width and the resulting change in the local density. The results obtained during the course of this project showed the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules. To the best of our knowledge, these have been the first demonstrations using the high sensitivity of single molecule tracing in characterizing self-assembled block copolymer morphologies.

The results obtained from this project have been the subject of an M.S. thesis in Materials Science and Engineering at Koç University. The results have been published as 1 journal paper in the Journal of Physical Chemistry B, and they have been presented in 6 international/national conferences.

Keywords: Single molecule tracing, total internal reflection fluorescence microscopy, diblock copolymer, terrylene, fluorescence imaging

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