Polymer Brushes for Molecular Transport - Paul Braun Research ...

PNIPAAm, though thin, may still allow for fast (relative to bulk) surface diffusion. Thus,
fluorescence would recover in the seemingly isolated PNIPAAm squares just as easily as it
recovered on unpatterned surfaces as is observed experimentally.
3.5 Conclusions
In conclusion, we have demonstrated a facile route for forming patterned PNIPAAm
brushes on oxide surfaces by microcontact printing of a surface initiator followed by the surface
initiated ATRP of NIPAAm. The patterning of the surface initiator was achieved by
microcontact printing octadecyltrichlorosilane followed by backfilling
aminopropyltriethoxysilane onto the unprinted region. The amino group was subsequently
reacted with bromoisobutyric acid forming the surface-grafted initiator. The surface-initiated
ATRP of NIPAAm was then carried out. The chemical structure of the PNIPAAm brushes was
confirmed by XPS and FT-IR, and the physical properties were characterized with ellipsometry,
contact angle measurements, and XRR. AFM confirmed successful micropatterning of the
PNIPAAm brushes. Environmental ellipsometry measurements showed that the LCST transition
of the PNIPAAm brush occurs over a broad temperature range of 20 to 35 °C. The fluorescence
emission spectra of Prodan in PNIPAAm brushes indicated that the local chemical environment
of the PNIPAAm is very similar to that of DMF. In addition, fluorescence microscopy suggested
that Prodan is localized in the patterned PNIPAAm brushes and excluded from the OTS regions.
The FRAP results of Prodan on PNIPAAm layers indicate that bulk translational diffusion, if
any is taking place, is at best very slow relative to other diffusion mechanisms. Isolating squares
of PNIPAAm brush with printed OTS lines does not eliminate the fluorescence recovery after
photobleaching entire isolated squares. Possible explanations for the fluorescence recovery
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