(246b) Structural Transitions of Nanoparticle Assemblies Mediated by Polymer Interactions at An Air-Water Interface

There is currently a large effort being invested in synthesizing and characterizing various types of nanoparticle assemblies, including quantum dots, plasmonic metal nanostructures, and varying aspect ratio particles such as tetrapods. These particles are useful when arranged into more complex structures and devices but finding strategies to order these structures has been difficult. One of the deterrents in following the ordering has been the inability to follow the details of the assembly process in real time. We will be presenting a method that track nanoparticle ordering at an interface with high spatial and temporal resolution in order understand the forces that control nanoparticle assembly. In particular, we are investigating the phase behavior of a polymer- nanoparticle assembly on an air-water interface. The system is a mixture of poly(L-lactic acid) (PLLA)and nanoparticles which are mixed together and placed on a Langmuir Trough. Various particle/polymer ratios are studied at different surface pressures. We find that phase separation and ordering of the particles exist for various surface pressures. For example, when surface pressure is around 20 mN/m, we observe a particle structure transition from nanoparticle islands to lassos, as observed via transmission electron microscopy (TEM). By tuning the concentration ratios of polymer and nanoparticles at constant surface pressure, we could achieve the same effects as well. Finally, we use Brewster Angle Microscopy (BAM) to monitor the structural ordering of the nanoparticles at the air-water interface in real-time.