Electrochemically Triggered Interfacial Deposition/Assembly of Materials

Abstract

Presented in this Dissertation is a new electrochemical methodology for surface deposition and interfacial assembly of materials. Using ferrocene-terminated self-assembled monolayers to electrochemically recruit polyelectrolytes and colloidal particles on electrode surfaces, I will detail herein the performance, mechanisms and application of this methodology. Specifically –

In Chapter I, a literature survey is given on research topics mostly related to this work: surface-bound electroactive molecular assemblies and interfacial assembly of materials. We find that several powerful and versatile strategies have been developed over the past few decades, enabling such broad applications as electrocatalysis, electrochemical sensors, molecular electronics, actuators, molecular photovoltaics, energy storage, and nanotechnology.

Chapter II describes a novel approach to surface deposition of polyelectrolytes on SAMs surface. This deposition process can be triggered facilely by a potential bias, which oxidizes ferrocene moieties included in the self-assembled monolayer to ferrocenium, whose charge compensation is fulfilled by polyelectrolytes and associated counterions. This approach is quite general, affording quantitative deposition of both polyanions and polycations with a wide range of chemical identities (synthetic polymers, peptides, and DNA) and molecular weights (1000−10000000 Da as tested). Conventional layer-by-layer polyelectrolyte deposition can be straightforwardly combined with this method to produce electroactive polymer films. Several techniques, including voltammetry, fluorescence spectroscopy, contact angle analysis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy (AFM) were employed to characterize the deposition processes. A detailed discussion on the involved deposition mechanisms is also presented.

Presented in Chapter III are our findings on employing the same electrochemical trigger, ferrocene oxidation, to achieve interfacial assembly of aqueous-suspended colloid particles. Using carboxylic-terminated polystyrene nano-/microbeads as a model colloid, we confirm first their transfer to and deposition at such redox active surfaces. Key factors involved, including the starting electrode surfaces, colloid size, range/duration of applied potential, and small supporting electrolytes, are examined in detail using voltammetry, EQCM, and confocal laser scanning microscopy. A particularly interesting finding among these is the superior efficiency of the electrochemically triggered assembly compared to the electrically driven process. Taking advantage of this feature, we demonstrate fast, high-fidelity colloid micropattern formation on electrodes at the end.

In Chapter IV, the utility of this new methodology is further extended to other types of materials such as metal and metal oxides nanoparticles, quantum dots, multi walled carbon nanotubes (MWCNTs), and soft materials such as liposomes. We employed atomic force microscopy and confocal laser scanning microscopy to characterize those deposits and/or deposited materials on electrode surfaces. Using liposomes with well-defined surface charge, enabled us to demonstrate mechanistic differences utilizing this approach for deposition of materials with positive, negative and neutral surfaces respectively.

Finally, in Chapter V, I will draw the main conclusions of my studies and offer an outlook of what might be done in the near future along this direction.