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Peter Collins Coatings Consultancy Ltd
An outline formulating strategy for paints will be proposed, reviewing past and current methodologies, including experimental design for modelling, with an eye to good practice leading to a sustainable future.
It turns out that the surface science community has provided surprisingly few tools relevant to those needing to produce functional coatings. An over-emphasis on ‘surface energy’ and DLVO, both of which involve much handwaving and surprisingly little good science, has meant that we have missed out on many tools that are much more insightful. In this talk, a number of such tools will be shown, live, via the apps that implement them, including the super-sophisticated Scheutjens-Fleer theory for dispersants/stabilizers which has been appified recently. All apps are free and Open Source. This appification of knowledge is a key way to allow busy formulators to test their formulation options. For those who need more depth than the explanations on the app pages, they can download free eBooks that go into more detail, yet link directly to the apps so you can see what the science means for your problems.
Smart coatings have the ability to interact with the environment, responding selectively to certain triggers, such as mechanical fracture, temperature or pH variations. Depending on the type of functionalisation different properties can be achieved, e.g. specific corrosion inhibition, self-healing or self-cleaning properties. This technology is widespread in the field of polymeric coatings, where the organic matrix can be easily functionalised; however, their applicability is limited to mild environments, since they usually present relatively low thermal and tribological resistance.
The scientific question proposed in this work is whether incorporating smart functionality is feasible in ceramic-based coatings produced by Plasma Electrolytic Oxidation (PEO). Such coatings present excellent performance in demanding conditions, but active functionalisation is highly challenging given the rigid and inert nature of inorganic matrices compared to organic materials. For that, the formulation of the coating includes nanocontainers loaded with corrosion inhibitors, which will be incorporated into the porosity of the coatings. The inhibitors are released from their nanocontainers in response to pH changes arising from electrochemical activity associated with corrosion initiation and will act locally at the anodic and/or cathodic sites inhibiting corrosion propagation.
At the epicenter of miniaturization, lies the role of materials and manufacturing methods by which they can be processed efficiently. At smaller inaccessible sub-micron scales, the underlying science of these two aspects is still developing which makes the progress on this front very slow. While digitalisation of the bottom of manufacturing processes such as a growth process, can help accelerate the process, the instrumentation development necessary to monitor these will take time. An accurate understanding of nanoscale deposition processes requires an insight into the energetic, structural, dynamic and rheological aspects of the system. Experiments alone would be insufficient to meet this need and hence there is a scope for using atomic simulation to expedite this process. Moreover, with the descend of scale, surface properties start to dominate the bulk properties of materials and the complex interplay of these together contributes to significant manufacturing challenges at the nanoscale. This impedes the insertion of newer materials in healthcare, aerospace, energy and electronics e.g., carbon fibre reinforced plastic (CFRP), carbon-based 2D materials, titanium alloys, nanopolymer composite coatings and semiconductor materials like silicon and its derivative. Hence understanding the relevant atomic level phenomena is the key to obtaining full knowledge of the atomistic mechanisms underlying the growth or material removal processes to obtain a usable quality of surface whether it is to be used for an optical or for an electronics application. The talk will be covering these silent aspects while shedding light on some of the early stage work done by the speaker in firstly understanding the material removal processes and showing how the same tools of simulation are equally useful to understand the vapour growth processes which is one of the activities undertaken by the speaker as part of the EPSRC DSMN+ project.
Diffusion in Coatings
Charlie Wand1, Simon Gibbon2,3 and Flor Siperstein1
1 Department of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
2 AkzoNobel Research & Development, Northallerton, North Yorkshire, DL7 7BJ, UK
3Department of Materials, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
The infrastructure of our modern society relies on large scale metal structures, which have a very large embedded carbon dioxide footprint. Protective organic coatings are key to sustainability as they extend the life of assets in aerospace, automotive, and freight by providing protection against corrosion. It has been considered that polymer coatings provide corrosion protection by forming a barrier to prevent mass transfer between the metal surface and the surroundings. However, it has been shown that water can permeate through these coatings and reach the metal surface [1]. Therefore the mechanism for corrosion protection is significantly more complex than originally assumed, with the transport of species through the coating playing a significant factor in corrosion protection properties of the coating.
Here we perform atomistic molecular dynamics simulations to investigate the diffusion of water through an epoxy-amine coating and investigate the effect of temperature, cross-linking (cure), and moisture content on the diffusion of water through the organic coating. We find that water diffusion is via a polymer-assisted hopping mechanism between isolated free volume nanoscale pores and that the polymer mobility is the determining factor for the speed of water diffusion [2].
[1] C. Grave, I. Mcewan, and R. A. Pethrick, Influence of Stoichiometric Ratio on Water Absorption in Epoxy Resins, J. Appl. Polym. Sci. 69, (1998).
[2] C. R. Wand, S. Gibbon, and F. R. Siperstein, A Computational Study of Water Diffusion through an Epoxy-Amine Thermoset Polymer, Prep. (n.d.).
Levelling additives find widespread use in industry to improve the surface properties of coatings and paints. Without such additives, many solvent-borne coating formulations are prone to excessive defect formation, significantly degrading their functionality and visual appearance. The origin of these defects can often be traced back to the high surface tension of the applied liquid film, preventing sufficient flow and levelling. Therefore, amphiphilic block copolymer additives are added to the formulation. These additives autonomously segregate to the coating surface and reduce the surface tension of the film. Although virtually every coating and paint formulation contains these levelling additives, much is still unknown about the influence of specific block copolymer properties and the effect of the coating matrix characteristics on the interfacial affinity of these amphiphiles.
I will discuss the main findings of our work in the investigation of the surface affinity, segregation, and phase behaviour of well-defined linear diblock copolymers containing an apolar polydimethylsiloxane (PDMS) and a polar polyether block, in a solvent-borne coating formulation, in the cured films and during the drying process. Exceptionally high surface enrichment was achieved, with significant silicon concentrations being detected within the top few nanometres of the coating layer. The characteristics of the polymer blocks, e.g. their size or chemical nature, as well as the monomeric composition of the acrylic binder were all shown to affect the additive behaviour and can thus be used to precisely tune surface properties of both the liquid film and the final cured surfaces.
Alistair Little
SBZ Corporation
The formulation of new coatings is often done by looking at existing formulations, then modifying them to meet the customers requirements. This presentation looks at a high performance solvent based polyamide-imide resin system that had high temperature properties, then reformulating it to both improve its flexibility and change the solvent system to water based for use as a binder system for a low friction coating. The presentation goes through the changes made to the base polymer to provide the improved properties, as well as the changes required to produce a water based system.
As part of the customer approval process, the internal testing required is examined, as well as some of the test methods. Since the customer was just going to purchase the base resin system, and blend the filler in themselves, results are shown of the customer trials with different filler systems. Finally some of the issues encountered during scale up from laboratory to production are discussed.