Janus Nanoparticles by Interfacial Engineering

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

This award to University of California Santa Clare by the Solid State Materials Chemistry program in the Division of Material Research is study the development of an effective protocol based on interfacial engineering for the preparation of nanometer-sized Janus particles, and examination of these functional nanomaterials as unique building blocks for the fabrication of more complicated architectures and assemblies. Specifically, hydrophobic alkanethiolate-protected gold nanoparticles will be used as the initial illustrating examples. By taking advantage of the impeded interfacial mobility of the particles at the air-water interface upon mechanical compression (the Langmuir method), the surface exchange reactions with hydrophilic thiol derivatives that are injected into the aqueous subphase will be confined to only one side of the particle surface, and hence the formation of amphiphilic nanoparticles. A wide array of analytical tools will then be employed to carefully examine the structures of the resulting particles and their organized ensembles, including contact angle measurements, scanning probe microscopy (e.g., AFM and STM), and spectroscopies (UV-visible, FTIR, NMR, dynamic light scattering, etc). Further manipulation of the Janus nanoparticles will focus on deliberate variation of the chemical structure of ligands and the metal cores. Overall, the capability of engineering the structure and properties of nanoscale building blocks for controlled assembly represents a critical first step towards device fabrication and integration. In this project, student researchers will benefit from the interdisciplinary nature of the work by learning the state of the art of nanoparticle synthesis, characterization, and assembly. Furthermore, some of the activities will also be closely integrated with several outreach programs targeting minority, women, and disadvantaged undergraduate students. In this project Prof. Shaowei Chen and his students at the University of California Santa Cruz, will develop an effective approach to the preparation of nanometer-sized particle materials that exhibit hydrophobic characters on one face and hydrophilic on the other. These particles are analogous to the dual-face Roman god, Janus, and hence Janus nanoparticles. The motivation is that by segregating the hydrophobic ligands from the hydrophilic ones on the particle surface, the particles may behave like the surfactant molecules of detergents, leading to directional assembly of the particles into organized structures. Gold nanoparticles stabilized by a monolayer of alkanethiolates will be used as the starting materials. Experimentally, a monolayer of the particles will be first formed on the water surface; and by mechanical compression (the Langmuir method) the mobility of the particles will be impeded because of intercalation of the organic protecting ligands from neighboring particles. Injection of a hydrophilic ligand into the water phase will then initiate ligand exchange reactions that are limited only to the bottom half of the particles, and hence the production of Janus nanoparticles. Further work will be extended to other nanoparticle materials. The resulting particles will then be used for controlled assembly into organized structures with unique functional characteristics. Student researchers will benefit from the interdisciplinary nature of the work by learning the state of the art of nanoparticle synthesis, characterization, and assembly. The research activities will also be integrated with various outreach programs targeting minority, women, and disadvantaged undergraduate students.