Author : Feipeng Yang
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (135 download)
Book Synopsis Nanoscale Characterization of Electrolyte Diffusion, Interface Morphology Disruption and Surface Dynamics of Polymer Melt Films Adsorbed on Graphene by : Feipeng Yang
Download or read book Nanoscale Characterization of Electrolyte Diffusion, Interface Morphology Disruption and Surface Dynamics of Polymer Melt Films Adsorbed on Graphene written by Feipeng Yang and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Significant efforts have been made to understand corrosion since it is important both scientifically and technologically, as the direct cost resulting from corrosion and its prevention has become a non-negligible portion of the gross domestic product. While considerable effort has been made to understand the macroscopic corrosion behavior and empirical knowledge of effective corrosion mitigation strategies is available, a nanoscale description of corrosion processes is still lacking. This dissertation describes efforts to establish a fundamental understanding of the corrosion process at the coating/metal interface on the nanoscale. The dissertation is divided into three parts. In the first part, a nanoscale depiction of the influence of ions on the diffusion of water is garnered from the analysis of X-ray and neutron reflectivity (XR/NR) and electrochemical impedance spectroscopy (EIS) data since metal, water and oxygen are three key ingredients in corrosion and ions play an important part in accelerating corrosion. The diffusion of water or electrolyte in thin polymeric films in different directions, parallel to the film or perpendicular to it, was distinguished. XR/NR measurements were used to probe the diffusion parallel to the film using a customized diffusion cell and that rate was found to be orders of magnitude larger than the diffusion rate in bulk epoxy. In contrast, when EIS data were analyzed using equivalent electrical circuit (EEC) model fitting, the penetration (diffusion perpendicular to the film) rate was found to be orders of magnitude smaller than the diffusion rate in bulk epoxy. Consistent results from XR, NR and EIS showed that the diffusion rates of electrolyte in both the lateral and perpendicular directions are lower than those of water (H2O/D2O), and that the higher the ion concentration, the lower the rate of diffusion. Reflectivity measurements probing at small (nm) length scales and also comparatively short times (hours) complement the widespread use of EIS and provide a means of quantitatively investigating phenomena that occur rapidly as a first step in the metallic substrate corrosion. The second part of this dissertation provides a detailed description of the changes in an epoxy/aluminum interface morphology that occur upon exposure of the interface to water or electrolytes, with information derived from X-ray off-specular scattering and atomic force microscopy (AFM). The interface is quantitatively described using a self-affine model of a randomly rough interface based on height difference correlation function with parameters of roughness, jaggedness, and correlation length. "Rocking curve" measurements show the interface becomes more rough, the texture becomes more jagged and the correlation length becomes smaller. Different electrolytes (NaCl and NaI aqueous solutions) have similar effects on the disruption of the interface morphology, and H2O is less disruptive to the interface as compared to the two electrolytes. In the last part of this dissertation, the surface fluctuations of polystyrene (PS) melt films adsorbed on graphene are compared to the surface fluctuations on films adsorbed on single crystal silicon wafers. The surface fluctuations on polymer thin films have received intense interest since surface fluctuations influence important interfacial properties such as wetting, adhesion, and tribology. Additionally, for sufficiently thin films the surface fluctuations also reflect realities of the chain adsorption and organization at the interface with the substrate and those features of films should be important for dictating the resistance to water or electrolyte incursion at a substrate/film or matrix/filler interface. For 8Rg thick entangled linear polystyrene (PS) films on silicon (8Rg PS/Si) the surface fluctuations can be described using a hydrodynamic continuum theory (HCT), which assumes the thin film viscosity is equivalent to the bulk viscosity throughout its entire depth. For 131000 g/mol linear PS, when the thickness of the film is less than 4Rg, the surface fluctuations show confinement effects and the fluctuations are slowed. The surface fluctuations for an 8Rg thick PS film on graphene (8Rg PS/Graphene) are three orders of magnitude slower than those on 8Rg PS/Si. The 170°C data from the 3Rg PS/Si, 8Rg PS/Si and 8Rg PS/Graphene samples collapse on a universal curve using a two-layer model with a 75 nm (ca. 7Rg) thick highly viscous layer on graphene and a 14 nm (ca. 1.5Rg) thick highly viscous layer on silicon. The layer left after a rinsing and drying procedure reflects a 2.4 times thicker strongly adsorbed layer on graphene compared to that on silicon. Thus the effect of adsorption of melt PS chains on graphene on dynamics of the chains near the graphene is far more profound than the effect of adsorption of PS chains on silicon. This remarkable slowing of material near the polymer/graphene interface could have important implications for the performance of other graphene containing composites and coating systems when the polymer is able to interact as strongly with graphene as does PS.
