Article pubs.acs.org/IECR
Computational Studies on Release of Corrosion Inhibitor from Layerby-Layer Assembled Silica Nanocontainer Megha Tyagi,† Bharat A. Bhanvase,*,‡ and Shekhar L. Pandharipande‡ †
Chemical Engineering Department, Vishwakarma Institute of Technology, Pune 411037, Maharashtra, India Chemical Engineering Department, Laxminarayan Institute of Technology, Nagpur 440033, Maharashtra, India
‡
ABSTRACT: The present study focuses on ultrasound assisted preparation of silica nanoparticle using Stober’s method and silica nanocontainers with an adsorption of polyelectrolytes (i.e., poly(diallyl dimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS)) and a corrosion inhibitor (benzotriazole) by the layer-by-layer approach. The benzotriazole was entrapped between the oppositely charged polyelectrolyte layers (i.e., PDADMAC and PSS). Field emission gun scanning electron microscopy and transmission electron microscopy analysis confirms the successful formation of spherical silica nanoparticles and layer by layer assembled silica nanocontainers. The effect of pH on responsive release of benzotriazole form silica nanocontainers was studied. Various semiempirical models were studied to predict the release mechanism of the benzotriazole. Root-mean-square errors of the predictions of these models were compared in order to select the best fitted model. An artificial neural network model was developed and used to predict the release of benzotriazole in comparison with the selected best fitted model.
1. INTRODUCTION Material degradation due to corrosion is an important issue of modern days that leads to rejection and depreciation of several commodity products. Nowadays, industries are also looking for new, efficient and nontoxic coating systems that are environmentally friendly and can meet current needs.1 Currently, two major approaches (i.e., an active and a passive) are being used for the corrosion protection.2 When passive (barrier) coatings get damaged, the active corrosion protection plays a significant role in decreasing the corrosion rate by releasing the corrosion inhibitor in the system.3−7 However, loading of corrosion inhibitor in the system in order to get its prolonged release, thereby long-term corrosion protection, is a main challenge in front of the researcher. The conventional loading of corrosion inhibitors in the different coating systems has several disadvantages like (1) too slow leaching or too high release of corrosion inhibitor for coating system, (2) high solubility of corrosion inhibitor leads to blistering and delamination of protective coatings and (3) semipermeable membrane allows the transport of water, causing destruction of the barrier layer. Therefore, there is a demand for the development of a new approach for the loading of environmentally friendly corrosion inhibitors that can give better corrosion protection by prolonged and smart release of it on demand. The new approach for corrosion inhibitor encapsulation is the development of nanocontainers that will encapsulate the desired corrosion inhibitor efficiently, keep the encapsulated material for longer time, prevent its leakage into the surrounding environment and protect the substrate from aggressive species. One of the preparation methods for nanocontainers is a layer-by-layer deposition of oppositely charged polyelectrolytes on the surface of template nanoparticles.3,4,8−10 In this method, there is a flexibility of employment of any type of charged species (i.e., polyelectrolytes) during the preparation of nanocontainers. The shell of © 2014 American Chemical Society
the nanocontainer is sensitive to the physical (pH change) and chemical changes in the surrounding medium that might influence considerably on the release of the corrosion inhibitor.6,11 Shchukin and Möhwald6 have fabricated different nanocontainers using layer-by-layer assembly of poly(diallyl dimethylammonium chloride)/poly(styrene sulfonate), poly(allylamine hydrochloride)/poly(styrene sulfonate) and poly(allylamine hydrochloride)/poly(methacrylic acid) polyelectrolyte bilayers on halloysite nanotubes and SiO2 nanoparticles. The corrosion inhibitor benzotriazole was loaded in between the polyelectrolytes and its release was reported to be higher in aqueous solution at alkaline or acidic pH. Sonawane et al.3 have also used a novel approach for the preparation of nanocontainers using layer-by-layer assembly of oppositely charged species of polyelectrolytes and inhibitor on the surface of ZnO nanoparticles. Further, the release properties of corrosion inhibitor benzotriazole from ZnO nanocontainers have been investigated and application of ZnO nanocontainers in anticorrosion coatings was studied. Also, Bhanvase et al.4 have fabricated a calcium zinc phosphate based nanocontainer, which was prepared by layer-by-layer assembly of polyelectrolytes like polyaniline and polyacrylic acid and the corrosion inhibitor benzotriazole in the presence of ultrasonic irradiations. The reported results of the corrosion rate analysis, Tafel and Bode plots of nanocontainer coatings on the mild steel panel showed significant improvement in the anticorrosion performance of the nanocontainer/alkyd resin coatings. The release of the corrosion inhibitor is pH responsive and its release will take place when there is a local pH changes in an alkaline or acidic region and diminish the corrosion process.12 Received: Revised: Accepted: Published: 9764
March 8, 2014 May 10, 2014 May 16, 2014 May 28, 2014 dx.doi.org/10.1021/ie5010064 | Ind. Eng. Chem. Res. 2014, 53, 9764−9771
Industrial & Engineering Chemistry Research
Article
Several articles have been published that indicate the use of micrometer sized containers for corrosion inhibition.13−15 The size of the container used in different applications in anticorrosion and multilayer coatings plays an important role. The release of corrosion inhibitor from micrometer size nanocontainer leads to the formation of cavities in the coating and these cavities allow the corrosion species to enter the coating, thereby increasing the corrosion phenomenon, thus decreasing the corrosion protection efficiency of the coatings. This problem can be resolved by the reduction in the size of the nanocontainers, thereby increasing the release rate on inhibitor due to increase in the surface area of the loaded nanocontainer. The smaller sized nanocontainer dispersion in the coating matrix will prove more homogeneous distribution of the encapsulated corrosion inhibitor.16 The reduction in the size of the template used can result in the formation of nanometer sized containers. It has been reported that the use of the ultrasound assisted approach for the preparation of nanoparticles (used as a template in the nanocontainer) will result in the formation of nanometer sized particles.17−20 The cavitational effects generated by the ultrasonic irradiation can result in physical and chemical transformations in the system. This improves the nucleation and solute transfer rate due to ultrasonic irradiations and leads to the formation of smaller sized nanoparticles. Furthermore, kinetics models reported in the literature can be used to study the corrosion inhibitor release from layer-bylayer assembled nanocontainers. These available kinetic models can signify the corrosion inhibitor release as a function of time. The kinetic study of the corrosion inhibitor release can be used to provide information about diffusion processes, matrix degradation. The kinetic models contribute to a better understanding of the processes occurring during inhibitor release and can facilitate the optimization of existing systems and the development of new efficient systems. In many cases, for sustained release of corrosion inhibitor, theoretical equations are not available, hence in some cases, more adequate empirical equations can be used. In recent times, the artificial neural network (ANN) is being frequently used as a reliable modeling technique for quick prediction of data for various engineering applications. ANN is a black box modeling tool that is inspired by the biological neural networks with applications in several areas that include prediction of parameters, modeling and optimization of complex processes, fault detection and diagnostics and control of operations involving nonlinear multivariable relationships.21−24 ANN has been effectively applied in diverse areas of chemical engineering such as process control, catalysis, membrane separations, reactor modeling, modeling of the distillation column, estimation of mass transfer coefficient for fast fluidized bed solids, fault diagnosis in chemical processes and so on.25−34 In the present work, an investigation of the release of benzotriazole from layer-by-layer assembled SiO2 nanocontainers in water at different pH values was carried out. SiO2 nanocontainers were prepared by the layer-by-layer deposition of PDADMAC, benzotriazole and PSS layers on SiO 2 nanoparticles. SiO2 nanoparticles, used as a template during preparation of nanocontainers, were prepared in the presence of ultrasonic irradiation in order to get smaller particle sizes. The responsive release and release rate of corrosion inhibitor was studied quantitatively in water maintained at different pH. The available theoretical and empirical kinetic models were used to investigate the release of corrosion inhibitor from SiO2
nanocontainers. An ANN model is developed by training and testing it with experimental results. The results of an ANN model are compared with a best fit model from the available equations. Finally, estimation of the various kinetic parameters and validation of kinetic models has been carried out.
2. EXPERIMENTAL DETAILS 2.1. Materials. Tetraethylorthosilicate (TEOS, 28%) was procured from TCI Chemicals and it was used without any further purification. Analytical grade ammonia and ethanol was purchased from Aldrich and used as received. Poly(diallyl dimethylammonium chloride) (PDADMAC, Mw ∼ 45 000) was received from SNF India and sodium poly(styrene sulfonate) (PSS, Mw ∼ 70 000) was procured from Doshian Chemicals, Pune, India). Both electrolytes were used without any further purification. Deionized water (conductivity of
