Professor Rick Davis, in the Chemical Engineering Department at Virginia Tech, talks about his QCM-D studies
Hello Professor Davis, could you please describe your QCM-D work at Virginia Tech?
Our application areas are the analysis of thin film deposition for nonlinear optics and biological applications, as well as polymer brush adsorption for steric stability of nanoparticles for biological applications.
QCM-D has allowed us to examine phenomena much more accurately and rapidly than with traditional QCM. Additionally, being able to measure the dissipation has allowed for calculation of film thicknesses and water content that we were unable to do before. It has proven to be, at a minimum, a complementary tool for each research project in our lab.
What specific questions are you trying to answer with the E4 system/QCM-D technology?
In the thin film area, the effects of polymer concentration and pH on film structure, composition, and adsorption kinetics has been studied for a PAH/PCBS system, Professor Davis explains. For the nanoparticle applications, the quality of the anchor group used to adsorb the polymer to the nanoparticle is being studied by observing behavior in different media, particularly biological analogs, Will Miles, a student in Professor Davis laboratory continues.
What data or answers, generally speaking, came from using QCM-D?
In the thin film area, a saturation concentration was observed for the PAH/PCBS system, where the mass adsorbed reached a plateau. Through an increase in pH, a higher mass adsorption was achieved due to a reduced charge density on the polymer chains, says Professor Davis. Additionally, through use of the Voigt model, thicknesses were obtained and compared to dry film values obtained from ellipsometry, allowing for calculation of water content in the films.
From the nanoparticle perspective, we noticed that the polymer-stabilized nanoparticles settled out of solution in phosphate buffered saline (PBS) but not in deionized (DI) water. We suspected that this was due to desorption of the polymer brushes and related to competitive adsorption of the phosphate with the anchor group used to attach the polymer to the nanoparticle surface, Professor Davis continues. The QCM-D was used to adsorb these polymer layers onto the surface, then expose to PBS to examine the effect on the polymer brush. Just as suspected, the polymer brushes did desorb with exposure to PBS. Additionally, through the addition of a hydrophobic polymer block, this desorption could be slowed down or even eliminated based on the polymer molecular weight, Will Miles comments.
And finally, what do you think about the support and education given by Q-Sense?
Q-Sense has, by far, the most friendly and helpful customer service that we deal with on a regular basis. The short course offered in Piscataway was extremely helpful and an enjoyable experience, Professor Davis and Will Miles agrees.
Want to know more about the work conducted in the Chemical Engineering Department at Virginia Tech? Start by looking at these publications: Journal of Applied Physics 104(5), 2008 and Langmuir 24(19), 10887, 2008
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