Experimental and Theoretical Investigation of Monolayer Phase Separation on Noble Metal Nanoparticles

Author: ORCID icon orcid.org/0000-0002-5407-5900
Merz, Steven, Chemical Engineering - School of Engineering and Applied Science, University of Virginia
Green, David, En-Mat Sci/Engr Dept, University of Virginia
Egorov, Sergei, As-Chemistry, University of Virginia

Monolayer protected nanoparticles (MNPs) have a wide variety of applications from catalysis and photonics to biosensing and drug delivery. However, characterization of ultrasmall MNPs (<10nm) has proven difficult with traditional experimental techniques, making the synthesis and design of these ultrasmall MNPs challenging. Our work looks to develop simple and robust characterization methods using both experimental and computational techniques.
Experimentally we use Transmission Electron Microscopy (TEM) to assess nanoparticle shape and size and Matrix-Assisted Laser Desorption and Ionization (MALDI) to assess the degree of order present in nanoparticle monolayers. In addition, we model the systems using both Self-Consistent Field Theory (SCFT) and atomistic simulations to model these nanoparticle monolayers. We are then able to calculate predicted MALDI spectrum from these simulations which allows us to directly compare theory and experiment.
We validate this method with our first paper looking at a monolayer with only isotopic differences (dodecanethiol (DDT) and deuterated dodecanethiol [D25]DDT) as our control monolayer with a physically mismatched monolayer (DDT and butanethiol (BT)) that should show signs of phase separation. Our work looking at these two types of monolayers shows strong matches confirmed our hypothesized morphologies which gives strong credence to our technique.
We use our method to explore the dynamics of phase separation in a variety multi-ligand nanoparticle monolayers. This method is first used to examine how various degrees of physical mismatch between ligands effect nanoprticle monolayer phase separation, giving us a detailed look at how small changes in chain length mismatch between ligands can lead to a range of differing striped monolayers. We then expand our method to look at patchy and Janus-like phases by examining multi-ligand nanoparticle monolayers with chemical mismatch. The modelling of chemically mismatched monolayers required the use of more accurate atomistic simulations with advanced Monte Carlo sampling. These more advanced computational techniques allows for an accurate modelling of Janus-like monolayer phase separation. The CBMC atomistic simulation is also shown to be even more versatile by de novo predicting monolayer phase separation in monolayers with a variety of physical and chemical mismatches which gives rise to the possibility of computational design of multi-ligand nanoparticle monolayers for applications in drug delivery, biosensing, and photonics.

PHD (Doctor of Philosophy)
Nanoparticles, MALDI-MS, Self-Assembly, Simulation
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