Subcategory: Materials Science
Room: Exhibit Hall A
Theresa Tsaggaris - University of Pennsylvania
Co-Author(s): Shawn Maguire, University of Pennsylvania, Philadelphia, PA; Connor Bilchak, University of Pennsylvania, Philadelphia, PA; Russell Composto, University of Pennsylvania, Philadelphia, PA.
We hypothesize that the 62K polystyrene will infiltrate the approximately 50-50 volume ratio nanoporous gold through the process of thermal annealing as a control. The process of thermal annealing will coarsen the bicontinuous structure of the nanoporous gold, increasing the pore size. By fixing the pore size before infiltration we can map infiltration as a function of polystyrene molecular weights. Methods We implemented a process of pretreatment for the nanoporous gold by annealing it for 3 hours at 175C. To quantify the effects of thermal annealing on pore size, we performed Small Angle X-Ray Scattering (SAXS). We created a bilayer stack of approximately 100nm nanoporous gold on top of an approximately 100nm layer of polystyrene on a silicon wafer. Through ex-situ thermal annealing for 3 hours at 150C, we infiltrated the gold with polystyrene. By the use of Atomic Force Microscopy (AFM) we were able to image the material as an Au50Ag50 alloyed material, as-cast nanoporous gold dealloyed, infiltration with 62K polystyrene for varying amounts of time to see the change in roughness of the material as a qualitative analysis of the composite. Through line scans we could quantify the change in roughness at the surface of the material as well. We repeated these processes with a range of polystyrene molecular weights, from 2K to 2000K, so observe how entanglement molecular weight affects the success of infiltration to analyze what constraints need to be altered in order to infiltrate across all molecular weights of polystyrene. Results Through AFM we were able to observe the change in structure in the metal. As we increase the time of annealing from 3 hours to 12 hours, gold particles connect to form bicontinuous networks and the pore sizes proportionally increase. In the pre-treated non-infiltrated samples, light spots are indicative of the presence of pores. Pre-treated and infiltrated gold images show that the pores appear to be much shallower and the image is overall much smoother than the non-infiltrated phase image. Not pre-treated and infiltrated gold images, in comparison, the phase images look very different. This is because the structure of the metal is changing while the polystyrene is simultaneously trying to go inside of the pores. While infiltrating, the gold particles are connecting to each other and while some pores may increase in size, other pores might get blocked by the changing metal so while some areas are smooth, other areas no infiltration occurrs at all. Pre-treating the gold allows for a more successful infiltration because the metal structure and the pore sizes are fixed. In our SAXS plots, we can see the trend that pore size increases as the time of annealing increases from 60nm to 85nm. In the plot itself the shifts in peak center are indicative of this trend. As a control we ran SAXS two samples of pre-treated gold not infiltrated and two samples of pre-treated gold that were infiltrated. The pore sizes in these samples are all essentially the same at 85nm as we would expect. This is indicative in the plot because the peak centers are all aligned around the same value whereas before the peak centers were skewed. This trend verifies that pre-treating the gold is effective in keeping the pore size fixed to maximize the amount of polymer that can infiltrate. Conclusions The structure of the As-Cast nanoporous gold consists of individual gold particles with pores where the alloyed silver once was. Upon annealing, the structure becomes a bicontinuous gold network which coarsens upon annealing. Through pre-heating the nanoporous gold, change in metal structure can be mitigated. Polystyrene can infiltrate the pores of the nanoporous gold via capillary rise infiltration (CaRI)4. Future Directions By performing Rutherford Back Scattering (RBS) and Elastic Recoil Detection (ERD) we can further quantify the success of infiltration. Through the use of ellipsometry, we can analyze the effects of polymer infiltration on optical properties as well as any changes in glass transition temperature that may occur to the polystyrene while in nanoconfinement.
Funder Acknowledgement(s): National Science Foundation (NSF); Louis Stokes Alliance for Minority Participation (LSAMP)
Faculty Advisor: Russell Composto, email@example.com
Role: I assisted in the determination of the most effective method for infiltration of the nonporous gold with polystyrene. I created all of the nonporous gold/polystyrene film bilayer stacks on silicon. I performed analysis of the polystyrene film thicknesses. I also assisted in analysis of the Atomic Force Microscopy (AFM) images and the Small X-Ray Scattering Plots.