This BRIGE award supports the study of gas expanded liquids (GXLs) as a novel processing media for the production of anisotropic, metallic nanoparticles; which display unique morphology-dependent properties. The research objectives are to 1) synthesize anisotropic nanoparticles using colloidal directed assembly within GXLs, 2) demonstrate effective methods for the rapid size-fractionation of anisotropic nanoparticles and deposition into uniform, ordered arrays using GXLs, and 3) gain a fundamental understanding of the interparticle interactions and surface forces that govern the synthesis and processing of anisotropic nanoparticles in GXLs. Previous work has investigated the use of GXLs (low-pressure mixtures of CO2 and organic solvents) and other tunable fluids for the synthesis and processing of ligand-stabilized, spherical metallic nanoparticles. Here tunable fluids, specifically GXLs, will provide sustainable means for the production of unique nanomaterials for diverse applications. Gold and silver nanorods in GXLs will be produced by developing a seed-mediated growth processes; coupled with GXL mediated processing to yield uniform nanorod populations and long-range, ordered nanorod arrays. Advanced characterization techniques and thermodynamic modeling will be employed to gain a fundamental understanding of the anisotropic nanoparticle synthesis and directed assembly to further enhance production and processing capabilities.
If successful, this work will advance knowledge in the field of nanomaterial synthesis and manufacture by campaigning two specific philosophies: 1) Sustainable methods of nanoparticle synthesis and processing are achievable and have significant advantages over conventional methodologies for large-scale, economic, and green nanomaterial production. 2) The fundamental driving force for the synthesis of anisotropic nanoparticles is kinetically controlled processes that result from directed assembly rather than conventional colloidal template mechanisms.
The premise of our research is to explore the synthesis and processing of metallic, rod-shaped nanoparticles that display unique size-dependent properties using green solvents. Current methods of nanorod synthesis often suffer from low yields, high size polydispersity, undesired surface chemistries, and contamination by residual surfactants from the synthesis. One of the most promising applications of gold nanorods is in the field of biomedical sensing, diagnostics, and therapeutics, especially in targeted drug delivery for cancer. In this respect, the surfactant used for high yield gold nanorod synthesis is highly toxic to cells. In this research we have successfully demonstrated the ability to perform surface ligand exchange reactions and effective removal of residual surfactant, using green chemistry methodologies. This work successfully demonstrated the use of gas expanded liquids for the rapid size-fractionation of nanorod particles and removal of excess surfactant. Gas expanded liquids are a unique class of green solvents that possess highly tunable thermophysical properties. By tuning the gas expanded liquid properties, we can selectively isolate nanoparticles based on their size, shape, composition and surface chemistry. This is especially pertinent for nanotechnology applications because the fundamental definition of a nanomaterial is one that possesses size and shape dependent properties. Furthermore, this work has lead to a greater fundamental understanding of solution-based synthesis and processing of metallic nanorods and the interrelations between anisotropic nanoparticle dispersibility and the solution properties. This work has contributed to the submission or publication of six peer-reviewed publications, two book chapters, and several technical presentations In addition to the research accomplishments, this work has contributed to the education of two Ph. D. students, six undergraduate researchers and two high school science teachers. Other outreach activities include demonstrations for high school classrooms and development of a new undergraduate level nanotechnology course at Clemson University.
