Abstract
Polyurethane based tri-block copolymers namely poly(N-vinylpyrrolidone)-b-polyurethane-b-poly(N-vinylpyrrolidone) (PNVP-PU) and poly(dimethylaminoethylmethacrylate)-b-polyurethane-b-poly(dimethylaminoethylmethacrylate) (PDMAEMA-PU) were synthesized through atom transfer radical polymerization (ATRP) mechanism. The synthesized polymers were characterized using nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) methods. The corrosion inhibition performances of the compounds were investigated on mild steel (MS) in 0.5 M H2SO4 medium using electrochemical measurements, surface analysis, quantum chemical calculations and molecular dynamic simulations (MDS). Potentiodynamic polarization (PDP) measurements revealed that the polymers are mixed-type corrosion inhibitors. Electrochemical impedance spectroscopy (EIS) measurements showed that the polymers inhibit MS corrosion by adsorbing on MS surface to form pseudo-capacitive interface. The inhibitive effects of the polymers increase with increasing concentration and decrease with increasing temperature. The adsorption of both the polymers on MS surface obey the Langmuir adsorption isotherm and involves both physisorption and chemisorption mechanisms. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed that the polymers formed protective film on MS surface and shield it from direct acid attack. Quantum chemical calculations and molecular dynamic simulations studies corroborate experimental results.
Highlights
Unhindered exposure to the aggressive/corrosive environment[14]
Two polyurethane based tri-block co-polymers namely, poly(N-vinylpyrolidone)-bpolyurethane-b-poly(N-vinylpyrolidone) (PNVP-PU) and poly(dimethylaminoethyl methacrylate)-bpolyurethane-b-poly(dimethylaminoethylmethacrylate) (PDMAEMA-PU) have been synthesized, characterized and tested for their corrosion inhibition performances on mild steel (MS) in 0.5 M H2SO4
The synthesized compounds were tested for their corrosion inhibition performances on mild steel in 0.5 M H2SO4 solution using electrochemical techniques, scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses
Summary
The values of Ea in the presence of inhibitors are generally greater than that of the acid blank (Table 3), suggesting that the polymer molecules adsorbed on the active sites on MS surface thereby raising the energy barrier associated with corrosion reaction. The values of ip and ic in the presence of PNVP-PU and PDMAEMA-PU are generally lower than that of the blank system, suggesting that the inhibitor molecules adsorbed on MS surface and influence the passivating behaviour of MS in 0.5 M H2SO4. The Cdl values in the presence of the inhibitors are generally lower than that of the blank acid system This suggests a decrease in local dielectric constant or an increase in the thickness of capacitive layer, which is attributed to the adsorption of inhibitor molecules on the MS surface[43]. Tendency to inhibit Fe corrosion than PNVP-PU and this observation is in agreement with the trend of %IE obtained from potentiodynamic polarization measurements
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