EXPLORATORY: Environmentally Friendly Formation of Self-Assembled Monolayers and Surface-Initiated Polymer Films in Carbon Dioxide

Vanderbilt University, Nashville TN

Investigators

Abstract

Abstract CTS-0203183 Jennings, G. Kane Weinstein, Randy D Vanderbilt University EXPLORATORY: Environmentally Friendly Formation of Self-Assembled Monolayers and Surface-Initiated Polymer Films in Carbon Dioxide This collaborative research will investigate the use of environmentally benign carbon dioxide (CO2) as a solvent in the formation of self-assembled monolayers (SAMs) and ultrathin polymer films grown by a surface-initiated process. Due to its small molecular size and weak interaction with metal surfaces such as gold, CO2 is a nearly ideal solvent to promote the formation of densely packed, highly crystalline SAMs, as recently reported by the authors of this project. Further research will examine the formation of SAMs onto gold from partially fluorinated alkanethiols and the effect of co-solvent on the structure and barrier properties of monolayer films. This research also seeks to correlate for the first time the surface-averaged structure and barrier properties of SAMs as obtained by reflectance-absorption infrared spectroscopy (RAIRS) and electrochemical impedance spectroscopy (EIS), respectively, with their microscopic properties such as domain size and defect content as determined by scanning probe microscopy (SPM). This research will also develop a new class of surface-initiated, living polymer films based on the synthetic process of polyhomologation. The films are initiated from a boron-terminated SAM and have the interesting property that the terminal groups of the polymer film can be selected to create a wide variety of surface compositions. During the growth of these films, the precursor molecules must diffuse through the growing film and react at the active boron site so that solvents that enhance the transport of the precursor through the film will increase the rate of film growth and the ultimate thickness of the films. Carbon dioxide is a potentially effective solvent for enhancing the growth of these novel polymer films due to its ability to swell many polymers, its low viscosity and zero surface tension, and the high diffusion rates of many small molecules in CO2. In addition, the use of CO2 in this polymerization process enables a much simpler one-pot synthetic procedure in contrast to the use of organic solvents that must be conducted with numerous solvent transfers in a dry box. To date, there has been no previous investigation of the use of CO2 in the formation of surface-initiated polymer films and only one other study involving the formation of SAMs in CO2. The successful completion of this project will provide new strategies for forming these technologically important ultrathin films through environmentally friendly processing. Furthermore, this project should enhance the knowledge base for materials processing in CO2 and facilitate the increased use of CO2 in research and industry.