Surface Functionalisation through Nanoscale Science

Gelatin microgels as a potential corrosion inhibitor carriers for self-healing coatings: Preparation and co-deposition

A. Stankiewicz*, Z. Jagoda, K. Zielińska and I. Szczygieł

Co-deposition of a coating with capsules containing a corrosion inhibitor is one of the methods to protect the material surface against corrosion. This generation of coatings can be regenerated in response to mechanical or chemical damage. The paper presents a method for preparing gelatin microgels that can be eco-friendly corrosion inhibitor reservoir. The influence of temperature, stirring rate, an addition of surfactants (ionic and non-ionic) on microgel quality has been studied. It has been found that the microgels obtained at 80 8C from the solution containing non-ionic surfactant at concentration below its critical micelle concentration are the most stable and less polydisperse one. As a proof of concept, a Ni-P\gelatin microgels hybrid coating has been obtained by electroless method.

1. Introduction

The selection of a construction material is most often based on a compromise between the desired properties and price. When insufficient surface properties are the only drawback of such a material, the top layer is covered by a protective coating. This solution allows to decrease the costs associated with the use of more expensive materials and bringing desired hardness, abrasion resistance, or other properties. In the context of corrosion protection, both inorganic and organic coatings are applied. They serve to protect various materials – magnesium or
aluminum alloys, steel, composites. Preventing and mitigating corrosion issues of structural and functional materials are a vast cost to modern industrialized economies. Until recently, the main components of anti-corrosion coatings have been chromium(VI) compounds. However, the current legislation levies by registration, evaluation, authorization, and restriction of chemicals (REACH) restricts the use of hexavalent chromium, because of their carcinogenicity. The introduction of limitations on the use of compounds containing chromium(VI) has become the impetus for the development of alternative coatings [1]. Nowadays, it is important that the protective layer has additional properties
being multifunctional. It should smartly defend itself against adverse effects of the external environment and adequately respond to mechanical or chemical damage. Moreover, applied technologies need to comply with both health and environmental legislation
[2,3]. 

Self-healing ability is a property of particular relevance for anti- corrosion coatings. Polymer, organosilicon, sol–gel, conversion, metallic, or ceramic coatings are used as self-healing layers. Among the self-healing coatings layers containing micro- or nano-capsules are of particular interest [4–8]. They consist mostly of macro- molecular compounds, i.e., poly(urea–formaldehyde), epoxy resin, poly(methylmethacrylate), polystyrene [6,7,9]. The capsules may be filled with appropriately selected corrosion inhibitors, for example cerium or magnesium ions, silyl ester, linseed oil, 8-hydroxyquinoline, benzotriazole. Recently, emphasis has been put on the search for eco-friendly materials that are the building blocks of corrosion carriers. The results of the studies on the use of silica, titania, CaCO3 microbeads, halloysite nanotubes, orboehmite nanoparticles have been described. Replacement of the capsules with microgels (micron-sized gel particles) is a new solution. Preparation of microgels containing a corrosion inhibitor is much simpler than capsules synthesis fallowed by their filling. In this case, the active compound may already be added during formation of the microgel. An example of such systems are polyurea microgel particles containing 2-methylbenzothiazole used in the anti- corrosion applications [10]. According to the best knowledge of the authors, there is no data describing the use of gelatin microgel as a carrier for corrosion inhibitor. In other fields of science, especially in the life and health sciences, microgels, including gelatin one, are used much widely. Microgels are carriers of drugs, bioactive substances and nutrients, optical nanobiosensors, agents reducing fat in food products, or material for anionic dyes removal [11–21]. Microfabrication technology, reverse micelles via photocrosslinking or water-in-oil emulsion method can be employed to obtain gelatin microgels [22–24].

A. Stankiewicz

School of Engineering & the Built Environment, Edinburgh Napier
University, 10 Colinton Road, Edinburgh EH10 5DT (United
Kingdom) E-mail: a.stankiewicz@napier.ac.uk

Z. Jagoda, I. Szczygieł
Department of Inorganic Chemistry, Wrocław University of
Economics, Komandorska 118/120, Wrocław PL 53345
(Poland)

K. Zielin´ska
School of Biological and Chemical Sciences, Queen Mary
University of London, Mile End Road, London E1 4NS (United
Kingdom)

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