Self-assembled monolayers as nucleation sites for electrochemical growth of conducting polymers

Optically flat polymer films of poly N-alkylpyrroles have been electrochemically polymerized on gold electrodes modified with self-assembled monolayers of bis({dollar}omega{dollar}-(N-pyrrolyl)-n-undecyl) disulfide (BPUS). The surface-confined pyrroles in BPUS serve as nucleation sites for the ordered growth of the polymer films. Polymer films formed on the BPUS-modified gold electrode are compared to analogous films formed at the bare gold electrode surface using cyclic voltammetry (CV), chronoamperometry (CA), scanning electron microscopy (SEM), optical microscopy, atomic force microscopy (AFM), and the electrochemical quartz crystal microbalance (EQCM). The microscopic techniques show that the films formed on the BPUS-modified electrodes are smooth and uniform in nature while those polymerized at the bare gold electrode are rough and amorphous in nature. Furthermore, visual evidence is provided confirming the reaction between the surface-confined pyrroles and monomer species in solution. CV and EQCM experiments show that the polymer growth on the modified electrodes is ordered and dense, while that on the bare electrode surface is of very poor quality. The possibility of producing well-ordered polymer films by controlling the nucleation process is clearly demonstrated. Self-assembled monolayers of various alkylthiols were also shown to be useful for influencing the crystallization of calcium carbonate and silver on self-assembly modified gold surfaces. In addition, Langmuir monolayers of silver n-octadecanethiolates were presented as a model for single lyers of self-assembled monolayers by mimicking the sulfur - gold bond. This aspect of the study employed in situ real-time ellipsometry in conjunction with surface pressure-area isotherm measurements to investigate the interfacial properties of the sulfur and metal ion complex. Brewster angle microscopy (BAM) was used to obtain real surface images with nanometer thickness resolution.