Abstract
Composite materials made of polymer and clay are effective at blocking mass transport. In this study, the blocking efficacy of layer-by-layer (LbL) coatings of exfoliated montmorillonite (MMT) and polyethylenimine (PEI) was studied using cyclic voltammetry and a redox couple, indigo carmine (IC). The pH of the MMT solution was varied from 4 to 10 to prepare LbL coatings of different surface roughness on metal substrates. It was found that the coated electrode had a lower redox peak current value than without the coating, demonstrating the reduction of the mass transport of IC to the metal surface. The peak values decreased with decreasing the coating’s roughness and increasing the number of layers, indicating that the blocking capability can be controlled by changing the deposition conditions. Smooth LbL coatings deposited with MMT at pH 4 showed the highest blocking efficacy up to 97.5%. The IC adsorbed at the interface between the coating and the metal substrate was found to cause the peak current measured for the coated electrode. It was also confirmed that the same coating on the copper substrate reduced the corrosion of the copper during the electrochemical potential cycling.
Highlights
Layer-by-layer (LbL) deposition is a versatile manufacturing technology that allows for the fabrication of thin films composed of polyelectrolytes, nanoparticles, and clay by utilizing electrostatic attraction between the components [1]
Compared to conventional bulk composite materials composed of polymer and clay, a multilayer coating of clay and polymer deposited by the LbL assembly method is more effective at blocking gas diffusion, flame retardation, and metal corrosion protection [5,6]
Using the LbL deposition method, a metal surface was coated with a multilayer of MMT and PEI
Summary
Layer-by-layer (LbL) deposition is a versatile manufacturing technology that allows for the fabrication of thin films composed of polyelectrolytes, nanoparticles, and clay by utilizing electrostatic attraction (or hydrogen bonding) between the components [1]. It allows for control of the thickness and structure of the coating in nanometer scale by adjusting the number of layers, concentration, temperature, and pH of the dispersion solution. Compared to conventional bulk composite materials composed of polymer and clay, a multilayer coating of clay and polymer deposited by the LbL assembly method is more effective at blocking gas diffusion, flame retardation, and metal corrosion protection [5,6]. LbL coatings of polymethylmethacrylate (PMMA) and MMT were shown to be effective at inhibiting the corrosion of Coatings 2020, 10, 1173; doi:10.3390/coatings10121173 www.mdpi.com/journal/coatings
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