Characterization of the electrode/SAM/electrolyte interface and intermolecular interactions in solutions using electrochemical impedance spectroscopy and ATR-FTIR spectroscopy

• Main Author: Protsailo, Lesia V
• Format: Dissertation
• Language: English
• Subjects: chemistry, analytical
• ISBN: 0493781781; 9780493781785

The importance and feasibility of the electrochemical impedance spectroscopy (EIS) applied to the studies of self-assembled monolayers (SAMs) was shown for both aqueous and nonaqueous electrolyte systems using alkanethiol and alkaneselenol films on gold electrodes.
An investigation of the kinetics of heterogeneous electron transfer for various redox couples has been carried out at single crystal electrodes modified by alkanethiols of varying chain lengths.
Careful study of the impedance of the modified electrode system in the absence of a reaction has shown that there is a highly resistive path in parallel to the capacitance due to the SAM. This element was used to investigate ionic permeability into SAMs deposited on gold electrode in propylene carbonate electrolyte solutions. The ionic permeability strongly depends on the applied potential and can be correlated with the potential of zero charge of the electrode. Increasing the temperature changes the ionic permeability of the SAM irreversibly. This is attributed to changes in film structure due to Ostwald ripening. An appropriate equivalent circuit for characterization of the ionic conductivity of these self-assembled monolayers was developed.
The formation and behavior of n-dodecaneselenol SAMs were also assessed by EIS. Microelectrode array theory was applied to study the growth kinetics of these SAMs. The results show that adsorption from a n-dodecaneselenol solution in ethanol can be described using two different time constants. The monolayer is formed within the first minute after the electrode has been brought into contact with the deposition solution. The second step involves film reorganization and self-ordering which can last for several hours.
ATR-FTIR spectroscopic studies were used in addition to electrochemical techniques to investigate intermolecular interactions in solutions of propylene carbonate. Quantitative correlation of the solvent-induced-frequency-shift was made using parameters chosen to describe the acid-base properties of organic solvents.