Mike Weir's abstract
Building 83 Conference Room (OPAL Visitor Centre).
Thursday 11:00 am
2 September 2010
"Voltage-induced swelling and de-swelling of weak polyelectrolyte brushes"
Dr. Mike Weir
Bragg Institute, ANSTO
Previous address: Department of Physics and Astronomy, The University of Sheffield, Sheffield, S3 7RH UK.
Polymer brushes are densely grafted layers of polymer molecules tethered at one end to a surface. By tuning the interactions between the neighbouring polymer chains, the degree of stretching and hence the brush conformation may be varied, producing a responsive surface coating with the thickness of a single macromolecule. If a polymer brush layer is present, surface properties such as wettability and affinity to protein adsorption are known to be dependent upon its conformation.
In this work, the conformations of poly(2-(dimethylamino)ethyl methacrylate) weak polybase brushes in response to externally applied voltages were investigated. The brushes were studied in water or D2O at neutral pH, with an electrode connected to the brush-bearing substrate and another parallel electrode some distance away in the surrounding liquid. DC voltages were applied between the electrodes and the resulting changes in conformation of the brushes were studied using ellipsometry and neutron reflectivity (ISIS, RAL, UK).
The positively charged brushes were shown to be swollen by a positive applied voltage (positive to the brush substrate) and de-swollen by a negative applied voltage, realising remote control of the conformation of the macromolecular layer. This work opens up a number of possibilities for electronically addressed smart surfaces, with potential applications in micro- and nano-fluidics. In combination with patterning techniques, surfaces could be pixellated to provide spatial control of the brush structure and potentially the transport of micro- and nano-scale cargoes across surfaces.