Faculty Achievement: Dr. Sean McBride

Dr. Sean P. McBride, assistant professor of physics at Marshall, has been part of a collaboration of investigators studying the mechanical response of self-assembled nanoparticle membranes when they are exposed to changes in temperature and other environmental stimuli. The collaboration’s research findings are presented in a recent publication in ACS Nano titled “Thermomechanical Response of Self-Assembled Nanoparticle Membranes.” The publication can be viewed at: http://pubs.acs.org/doi/abs/10.1021/acsnano.7b02676.

In addition to McBride, members of this collaboration included Dr. Yifan Wang, lead author currently at California Institute of Technology, who worked with research mentor and co-author Dr. Heinrich M. Jaeger at the James Franck Institute and the Department of Physics at the University of Chicago; fellow co-authors Drs. Henry Chan, Badri Narayanan, and Subramanian K. R. S. Sankaranarayanan; and Dr. Xiao-Min Lin, who are all researchers from the Center for Nanoscale Materials at Argonne National laboratory.

Recently, self-assembled nanoparticle monolayer membranes consisting of nanometer sized metallic or semiconducting particle cores capped with short organic ligands have attracted considerable attention. This is because these membranes can easily be formed via self-assembly techniques at liquid vapor interfaces and maintain the unique optical, electronic, or magnetic functionality of the core nanoparticles. These types of ultra-thin membranes have demonstrated potential uses such as drumhead resonators for potential use in sensors and filtration membranes for potential use in water purification applications. Understanding the mechanical response from these types of membranes under different external stimuli found in nature, such as temperature and humidity, is of great importance for use in such applications.

Abstract: Monolayers composed of colloidal nanoparticles, with a thickness of less than 10 nm, have remarkable mechanical moduli and can suspend over micrometer-sized holes to form free-standing membranes. In this paper, we discuss experiments and coarse-grained molecular dynamics simulations characterizing the thermomechanical properties of these self-assembled nanoparticle membranes. These membranes remain strong and resilient up to temperatures much higher than previous simulation predictions and exhibit an unexpected hysteretic behavior during the first heating−cooling cycle. We show this hysteretic behavior can be explained by an asymmetric ligand configuration from the self-assembly process and can be controlled by changing the ligand coverage or cross-linking the ligand molecules. Finally, we show the screening effect of water molecules on the ligand interactions can largely change the moduli and thermomechanical behavior.