Impact of molecular structure of two natural phenolic isomers on the protective characteristics of electropolymerized nanolayers formed on copper.

MARCOS BERTUOLA; DIEGO PISSINIS; ALDO RUBERT; EDUARDO PRIETO; MÓNICA FERNÁNDEZ LORENZO

ELECTROCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016

0013-4686

A comparative study of the electropolymerization of two natural phenolic compounds, carvacrol (Carv) and thymol (TOH) on copper was made. They are components of Origanum vulgare and Thymus vulgaris essential oils. Polymerized layers (polyCarv and polyTOH) were attained by cyclic voltammetry (CV). Electrochemical techniques complemented by ATR-FTIR, XPS, SEM and AFM surface analyses were used to evaluate the composition and protective characteristics of the films. Results revealed that the electrochemical response in chloride solutions was dissimilar. Copper ions release by polyCarv in chloride solutions was lower than 30% of that obtained with TOH treatments. PolyCarv is a highly protective, transparent film, remarkably different from the brownish, rough and non-protective film obtained with TOH. ATR-FTIR results showed that the oxidation of adsorbed Carv and TOH led to cetonic structures whileafter electropolymerization ether bonds were also found. However, polyCarv andpolyTOH showed important differences in OH band. Deconvolution of C1s signal ofXPS spectra led to four contributions with different proportions for polyCarv and polyTOH. Accordingly, C(ph)-O is 50% of total C1s for polyCarvCu and 30%for polyTOHCu. C1s/O1s relationships were also different. AFM and SEMobservations showed the presence of round flakes, smaller for polyCarvCu (5 nmheight) than for TOH (35 nm height). A compact layer was found in case of polyCarv but cauliflower and sticks structures with cracks were found for polyTOH. In summary,results showed the important impact of the molecular structure on the composition,structure and protective characteristics of the polymeric layers. A mechanism is proposed to interpret these results.