Chemistry PhD Final Defense — Kirill Gurdumov
About the event
Title: Self-Assembly Dynamics And Energetics At The Solution/Solid Interface: Concentration And Solvent Control
Abstract: A comprehensive investigation on the formation dynamics and energetics of adlayer formation at the at the solution/solid interface has been performed using scanning tunneling microscopy (STM) with a custom solution flow cell design that offers new insight into the self-assembly process. We herein investigate the growth, dynamics, and stability of a model non-covalent self-assembler — Co(II) octaethylporphyrin at the solution/solution interface on the HOPG and Au(111) surfaces. Real-time imaging of the nucleation and growth of the self-assembled layer was captured and studied by in-situ STM, and further explored using computational methods. Flow studies at low concentration provide insight into early-stage kinetics and structural formation of a SAM. It was found that the choice of organic solvent plays a dramatic role in the kinetics and structure of the SAM. The role of the solvent was particularly strong in the case of 1,2,4-trichlorobenzene (TCB) on both HOPG and Au(111). Under TCB, a very stable rectangular structure is formed and stabilized by solvent-incorporation. A transition to a solvent free pseudo-hexagonal structure was only observed when extremely high concentrations of porphyrin were present in solution. Similarly, in the case of CoOEP adsorbed on Au(111) under toluene, a solvent-incorporated rectangular structure was observed that also transitioned into a pseudo-hexagonal structure, but this transition occurred at much lower concentrations of porphyrin. Toluene co-adsorption was not observed on HOPG. When deposited from decane, a short-lived pseudo-rectangular structure was observed on Au(111) but not on HOPG. Only the pseudo-hexagonal structure was observed in the porphyrin adlayer when 1-phenyloctane were used as a solvent. These results provide insight into the balance of the intermolecular forces driving the self-assembly and the roles the choice of solvent and substate play in the formation process.