Stimulus responsive polymers undergo reversible physical and chemical changes in response to environmental stimuli such as temperature or pH. Catalyst performance can be improved through the use of such polymers, as they can expose or hide the metal site.
Temperature responsive polymer brushes will be coated on silicon surfaces containing metal nanoparticles and the effect of temperature, and hence brush conformation, has on the chemisorption of a probe molecule will be studied. Such polymers undergo a hydrophilic to hydrophobic change as a function of temperature; a so-called lower critical solution temperature (LCST). Temperature below or above the LCST, will therefore affect the diffusion of the probe molecule towards the metal site. Hydrophilic brushes are highly swollen and extended and should allow the probe molecule to diffuse closer to the metal site. CO chemisorption measurements will be performed using ATR-IR spectroscopy (attenuated total reflection infrared) to provide direct information about the state of the active sites and the structure of surface species. The temperature responsive brushes will be synthesized using controlled radical polymerization. Activators continuously regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) will be used as it is an environmentally friendly and oxygen sensitive controlled polymerization. Another parameter that can be measured is the thickness of the brushes, for that ellipsometry can be used. Also, thermogravimetric analysis (TGA) is another way to study the polymer brushes which the molecular weight is studied with the increase of the temperature.
This project will be focused on understanding the influence of brush thickness on catalyst performance. Here, poly(N-isoproylacrylamide) (PNIPAM) brushes will be synthesized and by controlling the polymerization rate and growth time, brushes of varying thicknesses can be produced. Control over polymerization rate can be easily achieved by changing solvent composition. The LCST (or temperature response window) is a function of the polymer molecular weight (MW). This allow us to increase the LCST by growing longer polymers brushes.
Maria E. Dasilva