PhD Dissertation Defense of Howard Dobbs


Wednesday, September 26, 2018 - 9:00am


ESB 2001


Howard Dobbs

Title: Role of Electrostatic Forces on Non-equilibrium Processes at Confined Inorganic Solid-Liquid-Solid Interfaces

Advisors: Brad Chmelka and Jacob Israelachvili


Non-equilibrium processes at confined solid-liquid-solid interfaces are prevalent in a wide range of naturally occurring and technologically relevant phenomena such as corrosion, molecular network formation, dissolution and restructuring. Nevertheless, the complex interactions within the interface inhibits an understanding of the physicochemical driving forces behind the evolution of the interface and subsequent development of macroscopic properties.  This is largely due to the difficulties associated with characterizing the influence of molecular-level interactions on macroscopic changes within systems which evolve over time.

The principle focus of this presentation will be on understanding the influence of electrostatic forces on the enhancement of dissolution processes at confined solid-liquid-solid interfaces. We determine the influences of electrostatic surface potential and ionic strength on the enhanced dissolution of alumina and silica in confinement (< 3 nm) with dissimilar charged surfaces in aqueous environments using a Surface Forces Apparatus (SFA). We find more rapid dissolution of alumina and silica in close proximity to mica compared to isolated alumina or silica materials in bulk solutions, consistent with previous observations. Furthermore, we demonstrate that the dissolution of silica in close proximity to a gold electrode in weakly alkaline solutions depends on the applied electrostatic potential. We propose that the enhanced dissolution phenomenon results from overlap of the electrostatic double layers between the dissimilar charged surfaces at small inter-surface separation distances (< 3 nm). A semi-quantitative model shows that overlap of the electrostatic double layers changes the magnitude and direction of the electric field at the surface of the dissolving material, which our results suggest increase the rate of dissolution of the surface with the higher potential. We show that dissolution rates of silica and alumina can be increased by up to two orders of magnitude by changing the surface electrochemical properties and solution conditions. Our findings yield fundamental insights into the influences of electrostatics on dissolution processes at asymmetric solid-liquid-solid interfaces and provide new methods for manipulating dissolution relevant to diverse technological applications.

The methods, analyses, and resulting insights on the importance of molecular interactions in dissolution processes at confined solid-liquid-solid interfaces are expected to be broadly relevant to non-equilibrium processes in similar environments and establish critical parameters to directly influence the evolution of macroscopic properties at confined interfaces.

Event Type: 

General Event