Brian Hinderliter

Thermal Cycling of Epoxy Coatings Using Room Temperature Ionic Liquids

Nonaqueous room-temperature ionic liquids (RTILs) offer a method of using electrochemical impedance spectroscopy (EIS) to analyze coatings without the confounding effects, such as plasticization, associated with an aqueous working fluid. Thermal cycling has been used as an accelerated testing method for ranking the corrosion protection of coatings. The influence of thermal cycling on the degradation of a coating was investigated using a hydrophilic RTIL as the electrolyte for the drying cycle of EIS experiments. The change in diffusion coefficient, saturated water volume fraction, and activation energy for the absorption and desorption of water by the coating was obtained.

Simulation of Wet-Dry Cycling of Organic Coatings Using Ionic Liquids

The capacitance evolution of an organic coating undergoing cyclic wetting and drying conditions was monitored by single frequency electrochemical impedance spectroscopy. Monitoring of the drying condition was possible with the use of a hydrophilic room temperature ionic liquid and the methodology employed is presented. Experimental results associated with cyclic dilute NaCl wetting and ionic liquid drying are presented for an epoxy coating on an AA 2024-T3 substrate. The calculated capacitance evolutions associated with wetting and drying were generally consistent with Fick’s second law. The calculation of the water ingress and egress diffusion coefficients using a short-time approximate solution and a series solution to Fick’s second law are presented. The latter solution is shown to address the capacitance evolution better than the former with the ingress coefficient larger than the egress coefficient for a given exposed coating surface. There was agreement between the calculated diffusion coefficient ingress values for coating areas exposed to cyclic NaCl wetting—ionic liquid drying and cyclic NaCl wetting—natural drying conditions. Comparison of the impedance spectra for test areas indicated that the use of the ionic liquid as a drying medium influenced the electrochemical properties of the coating only after a number of cycles.

Monte carlo approach to estimating the photodegradation of polymer coatings

The degradation of a polymer coating and predicting the coating lifetime based on physical properties and distribution within the coating of the polymer binder, pigments, and fillers are economically very important. As technologies advance and allow for control of coatings at the nanoscale level, methods such as Monte Carlo can be used not only to predict the behavior of a nanodesigned coating with time but also to design coatings, such as optimizing pigment particle distributions or optimum hard and soft phase distributions of the binders in multiphase systems for maintaining the desired property with time. Erosion of the coating surface was simulated using Monte Carlo techniques where terrestrial solar flux is the initiator for polymer segment cleavage and removal. The impact on the sensitivity of the polymer adjacent to the detached polymer segment can be increased or decreased in the model based on the chemistry and surface energy of the remaining polymer matrix. Multiple phases with varying sensitivity to degradation can be modeled. The Monte Carlo generates a statistically similar surface topography and chemistry of the coating. The results of the Monte Carlo model are compared to measurable properties such as gloss, fracture toughness, and wetting contact angle, using various published correlations of the property to the surface topology. The simulated properties change through the life-time of the coating in ways that are consistent with observed behavior. Apparently, complicated changes in many properties can be described by the repeated application of simple, random processes.

Monte carlo approach to estimating coating service lifetime during weathering

SummariesChange in a coating surface, or bulk, during weathering is the accumulation of repeated, random, nanoscale erosion or chemical events that may be modelled using Monte Carlo techniques. Multiphase coatings, including pigments, may be simulated, as well as polymers that change their sensitivity to degradation during weathering. The results of the Monte Carlo model are compared with those of macroscopic properties, such as, gloss, fracture toughness, and wetting contact angle. Simulated properties change through the lifetime of the coating in ways that are consistent with published results. Seemingly complicated changes in properties may be described by repeated simple, random processes.RésuméLes changements produits dans la surface ou dans la masse des revêtements pendant leur exposition aux intempéries sont dus à une érosion aléatoire répétée ou à des événements chimiques et ils peuvent être modelés grâce à l’usage des techniques Monte Carlo. Les revêtements multiphase, y compris les pigments, peuvent être simulés aussi bien que les polymères qui changent leur sensibilité à la dégradation pendant leur exposition aux intempéries. Les résultats du modèle Monte Carlo sont comparés à ceux qui sont produits par des propriétés macroscopiques tel que le brillant, la résistance à la fracture et l’angle de contact du mouillage. Les propriétés simulées changent au cours de la vie des revêtements de façons compatibles avec les résultats publiés. Des changements apparemment compliqués dans le domaine des propriétés sont capables d’être décrits par le moyen des procédés simples et aléatoires.ZusammenfassungÄnderungen in der Lackoberfläche durch Witterungseinflüsse sind das Ergebnis von wiederholter, ungerichteter Nano-Erosion oder von chemischen Reaktionen, die mit der Monte Carlo Technik im Modell dargestellt werden können. Monte Carlo erlaubt es, Multiphasenlacke, inklusive Pigmente zu simulieren, sowie Kunststoffe mit wechselnder Anfälligkeit für Degradation durch Witterungseinflüsse. Wir vergleichen das Ergebnis des Monte Carlo Modells mit makroskoptischen Eigenschaften wie Glanz, Frakturbeständigkeit und Benetzungswinkel. Die simulierte Veränderung von Eigenschaften im Laufe der Lebensdauer des Lackes stimmen mit beobachteten Ergebnissen überein. Scheinbar komplizierte Veränderungen der Eigenschaften lassen sich durch wiederholte einfache Prozesse erklären.

Investigation of cement–sand-based piezoelectric composites

A novel cement–sand-based piezoelectric smart composite was developed for conducting structural health monitoring for civil structures. To overcome the incompatibility between piezoelectric materials and reinforced concrete containing cement and sand, for the first time, sand was used to fabricate the new composite in this study. Two sets of specimens containing 30 and 50 vol% lead zirconate titanate were prepared using normal mixing and spread methods, followed by the characterization of the properties of the composites. The composite exhibited desirable piezoelectric strain and voltage coefficients. Furthermore, the dielectric constant and loss of the composite were also determined. The results indicated that the piezoelectric effect and dielectric constant were enhanced with increasing lead zirconate titanate content. Compressive tests were conducted to study the sensing effect of the composite. The investigation demonstrated the feasibility of using the new composite as sensors in structural health monitoring systems to prevent possible failure of civil structures.

Analytical study of tensile behaviors of UHMWPE/nano-epoxy bundle composites

Ultra-high molecular polyethylene (UHMWPE) fiber reinforced nano-epoxy and pure epoxy composites in bundle form were prepared and tested for tensile properties. UHMWPE fiber composites are well known for their superior tensile performance, and this work was conducted to assess the effect of adding nanoadditives to the resin and to evaluate possible enhancements or degradations to that attribute. The results showed that tensile tests on various types of UHMWPE fibers/nano-epoxy bundle composites resulted in an increase in modulus of elasticity due to the addition of small amounts of reactive nanofibers (r-GNFs) to epoxy matrix. It was observed that the modulus of elasticity of the composite bundles depended on both volume fractions of the matrix and the weight percent (wt%) of r-GNFs in the matrix. A non-linear relationship was established among them and an optimal modulus was determined by calculation. A three-dimensional surface plot considering these two parameters has been generated which gives an indication of change in modulus of elasticity with respect to volume fraction of matrix and wt% of r-GNFs in the matrix. A Weibull analysis of tensile strengths for the various bundle composites was performed and their Weibull moduli were compared. The results showed that presence of r-GNFs in the composites increased the strength effectively, and 0.3 wt% r-GNFs based composites showed the highest strength. An important ancillary finding is that optimum tensile values are a function not only of the above parameters, but also strongly influenced by the addition of diluents which control the viscosity of the blend.

Simulations of nanoscale and macroscopic property changes on coatings with weathering

Coatings are designed for and applied on a surface for both aesthetics and protection of the substrate. Many properties are measured to indicate performance, and eventual failure, of a coating under these two broad categories. Monte Carlo simulations have shown success in predicting trends in macroscopic properties during exposure. The Central Limit Theorem (CLT) is applicable because damage made to a coating can come from the accumulation of a vast number of very small damage events. Application of the CLT to property equations has generated additional equations for the prediction of properties of a coating with exposure, including measurable properties such as gloss, color, fracture toughness, and contact angle. These equations, when fitted to measured data, provide in sight into the mechanisms of degradation processes, since the fitting parameters are physically based. They also offer a means to scale accelerated testing measurements to early field measurements of the property of interest for predicting lifetime in varied environments.

Predicting Coating Failure using the Central Limit Theorem and Physical Modelling.

In service, coatings are assaulted by huge numbers of ultraviolet photons, moisture molecules, pollutant molecules, thermal or other stresses with additional, occasional insults. Individually, these arrive at indeterminate times and locations so either Monte Carlo simulations or the statistics of random processes can be used to estimate the accumulation of damage. These damage results can then be used to calculate the deterioration in coating properties using well-known and robust physical models. In this way, not only can appearance properties like gloss and yellowing be modelled, but also the coating integrity via its fracture toughness or barrier properties, via electrochemical impedance. Additional physical detail or processes may be included, at several points, to produce a more complete predictive simulation or interpretative scheme. Simple calculations of how accelerated weathering affects coating service lifetime demonstrate how inconsistencies may arise between accelerated testing and natural exposure.

Evaluation of Corrosion Growth on SS304 Based on Textural and Color Features from Image Analysis

ime. The results obtained from the image analysis are presented to illustrate the metrics which best characterize early stage corro sion damage growth behavior. The results obtained indicate that textural features in combination with color features are more effective and may be used for correlating service/failure conditions based on corrosion morphology.

Army Vehicle Primer Properties During Wet-Dry Cycling

Abstract The standard QUV/Prohesion accelerated testing method simulates weathering conditions by exposing coatings to alternating wet and dry conditions. The degradation of the coatings is influen...