Diffusion in Polymer Nanocomposites Karen I. Winey, University of Pennsylvania, DMR 0908449.
Polymer motion through a highly crowded system was measured and found to match a theory originally developed for diffusion in random media, such as proteins through gels. The highly crowded system was achieved by uniformly dispersing spherical, silica nanoparticles (NPs) at concentrations up to 50 vol% in a polystyrene matrix. Polymer diffusion slowed down as NP concentration increased and this reduction was strongest for the largest polymers. The master curve shown at the right collapses the polymer diffusion data from three polymers onto a single curve when the NP-NP separation (given by ID) is normalized by the size of the polymer (given by Rg).
These results are in excellent agreement with the entropic barrier model that was originally developed for protein transport through a pore and provide the first experimental conformation of this model.
50 vol% NP
2 vol% NP
As the NP-NP separation (ID) increases relative to the polymer size (Rg), the polymer motion increases. Inset shows TEM images of polymer nanocomposites which is the crowded media.
Diffusion in Polymer NanocompositesKaren I. Winey, University of Pennsylvania, DMR 0908449
In a joint senior project , UPenn undergraduate’s Jen Ehrich and Shaina Oake explored the rheological properties of polymer nanocomposites. Rheology is not part of the undergraduate materials science curriculum, so there was much independent learning. They also interacted with collaborators from Durham University and DuPont.
Team members visited each other at UPenn and Durham University where graduate students and postdocs were able explore to differences between research practices at home and abroad with their peers.
(Left) Prof. Nigel Clarke (Durham Univ.) and Jen Ehrich (UPenn) measuring the rheological properties of nanocomposites using a Rheometrics RSA II rheometer in Dec. 2009.
(Right) Kristin Metkus (UPenn) and Vikki Bird (Durham Univ.) holding one of the nanocomposites they prepared together.