Even though the physics of nanoconfined polymers have
been extensively
studied for years, diffusion of polymer chains along confining interfaces
has not been widely studied, likely because there are few experimental
techniques available for these measurements. Here a fluorescence recovery
after patterned photobleaching (FRAPP) technique is developed using
an epifluorescence microscope that allows for direct, in situ, visualization of polymer diffusion over several periods of a photobleached
array. This visualization approach is more robust compared to measuring
fluorescence intensity alone and also significantly increases the
experimental throughput. Using this technique, self-diffusion of poly(isobutyl
methacrylate) (PiBMA) was investigated at 80 °C (29 °C above
the glass transition temperature, T
g)
and was found to be film thickness independent down to 30 nm (∼14R
g, where R
g is the
radius of gyration) with a diffusion coefficient well predicted by
the Rouse model (1.05 × 10–12 cm2/s). PiBMA is an ideal polymer for this study because it exhibits
a film thickness-independent T
g down to
15 nm (∼7R
g) as measured by spectroscopic
ellipsometry. Since the diffusion coefficient of polymers depends
strongly on the proximity of diffusion temperature to T
g, this attribute allows a straightforward measure of
nanoconfined diffusion without superimposed influence from T
g nanoconfinement effects.
A comparative study of chain conformation at the surface of poly(βbenzylLaspartate) and poly(γbenzylL glutamate) films with high resolution electron energy loss spectroscopy
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