Funding from the Australian Research Council Industrial Transformation Research Hubs Scheme (Project Number IH130100017) is gratefully acknowledged. Authors gratefully acknowledge the RMIT Microscopy and Microanalysis Facility (RMMF) for providing access to the characterisation instruments. This research was also undertaken on the Infrared Microscopectroscopy beamline at the Australian Synchrotron, Victoria, Australia.

1. Steel Samples
<ol>
	<li>Obtain steel samples of 1 mm thickness from a commercial supplier. 
	NOTE: Samples were coated with either polyester or polyester coated with silica nanoparticles.</li>
	<li>Expose samples to sunlight at Rockhampton, Queensland, Australia: collect samples after one-year and five-year intervals over a total 5-year period. Cut sample panels into round discs of 1 cm diameter using hole puncher.</li>
	<li>Prior to surface characterization, rinse samples with double-distilled...

<ol>
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Polyester coatings have been widely used to protect steel substrata from the corrosion that would occur on an uncoated surface due to the accumulation of moisture and pollutants. The application of polyester coatings can protect the steel from corrosion; however the longer-term effectiveness of these coatings is compromised if they are exposed to high levels of ultraviolet light under humid conditions, as occurs in tropical climates. Silica nanoparticles can be applied to the surface of the polyester to improve the robus...

Environmental corrosion of metals in the environment is both prevalent and costly1-3. A recent study conducted by the Australasian Corrosion Association (ACA) reported that corrosion of metals resulted in a yearly cost of $982 million, which was directly associated with the degradation of assets and infrastructure through metallic corrosion within the water industry4. From an international perspective, the World Corrosion Organization estimated that metallic corrosion was responsible for a direct cost of $3.3 trillion, over 3% of the world's GDP5. The process of galvanizing as a corrosion preventative method has been widely used to increase the lifespan of steel material6. In humid and subtropical climates, however, water tends to condense into small pockets or grooves within the surface of the galvanized steel, leading to the acceleration of corrosion rates through pit corrosion7,8. Thermosetting polymer coatings based on polyesters have been developed to coat the galvanized steel substrata increasing their ability to withstand humid weathering conditions for items such as satellite dishes, garden furniture, air-conditioning units or agricultural construction equipment9-11. Unfortunately polymer coatings on steel surfaces have been found to be considerably adversely affected by the presence of high levels of ultraviolet (uv) radiation12-14. Coatings comprised of silica nanoparticles (SiO2) spread over a polymer layer have been widely used with a view to increasing their corrosion-, wear-, tear- and degradation-resistance15,16. The tendency of the protective polymeric coatings to form pores and cracks can be reduced by incorporating nanoparticles (NPs), which contribute to the passive obstruction of corrosion initiation17,18. Also, the mechanical stability of the protective polymeric layer can be improved by NPs inclusion. However, these coatings act as passive physical barriers and, in comparison to the galvanization approach, cannot inhibit corrosion propagation actively.
An in-depth understanding of the effect that high-levels of ultraviolet light exposure under humid conditions upon these metal coatings is yet to be obtained. In this paper, a wide range of surface analytical techniques, including X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared micro-spectroscopy (ATR IR), contact angle goniometry, optical profiling and atomic force microscopy (AFM) will be employed to examine the changes in the surface of steel coatings prepared from polyester- and silica nanoparticle-coated polyester (silica nanoparticles/polyester) after exposure to sunlight. Furthermore, the aim of this work is to give a concise, practical overview of the overall characterization techniques to examine weathered samples.

<table border="0" cellpadding="0" cellspacing="0" width="1044">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="41">
			<td height="41" style="height:41px;width:263px;">polyester-coated steel 
			silica nanoparticle-polyester coated steel substrata</td>
			<td style="width:231px;">BlueScope Steel</td>
			<td style="width:163px;"></td>
			<td style="width:387px;">Samples provided by company</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:263px;">Millipore PetriSlideTM&#160;</td>
			<td style="width:231px;">Fisher Scientific</td>
			<td style="width:163px;">PDMA04700</td>
			<td>Storing samples</td>
		</tr>
		<tr height="49">
			<td height="49" style="height:49px;width:263px;">Thermo ScientificTM K-alpha 
			X-ray Photoelectron Spectrometer</td>
			<td>Thermo Fisher Scientific, Inc.</td>
			<td>IQLAADGAAFFACVMAHV</td>
			<td>Acquire XPS spectra</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">Avantage Data System</td>
			<td>Thermo Fisher Scientific, Inc.</td>
			<td>IQLAADGACKFAKRMAVI</td>
			<td>Analyse XPS spectra</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">A Bruker Hyperion 2000 microscope&#160;</td>
			<td style="width:231px;">Bruker Corporation</td>
			<td style="width:163px;"></td>
			<td>Synchrotron integrated instrument</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bruker Opus v. 7.2</td>
			<td style="width:231px;">Bruker Corporation</td>
			<td style="width:163px;"></td>
			<td>ATR-IR analysis software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">Contact angle goniometer, FTA1000c</td>
			<td>First Ten &#197;ngstroms Inc., VA, USA</td>
			<td style="width:163px;"></td>
			<td>Measuring the wettability of surfaces</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:263px;">FTA v. 2.0</td>
			<td>First Ten &#197;ngstroms Inc., VA, USA</td>
			<td style="width:163px;"></td>
			<td>Anaylyzing water contact angle</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Optical profiler, Wyko NT1100&#160;</td>
			<td>Bruker Corporation</td>
			<td style="width:163px;"></td>
			<td>Measure surface topography</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Innova atomic force microscope&#160;</td>
			<td>Bruker Corporation</td>
			<td style="width:163px;"></td>
			<td>Measure surface topography</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:263px;">Phosphorus doped silicon probes, MPP-31120-10</td>
			<td>Bruker Corporation</td>
			<td style="width:163px;"></td>
			<td>AFM probes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Gwyddion software</td>
			<td style="width:231px;">http://gwyddion.net/</td>
			<td style="width:163px;"></td>
			<td>Software used to measure optical profiling and AFM data</td>
		</tr>
	</tbody>
</table>

the evolution of silica nanoparticle-polyester coatings on surfaces exposed to sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

The coated steel samples that had been subjected to exposure to the sunlight for either one or five years were collected, and water contact angle measurements were carried out to determine whether the exposure had resulted in a change in the surface hydrophobicity of the surface (Figure 2).
<img alt="Figure 2" src="/files/ftp_upload/54309/54309fig2.jpg" /> 
Figure 2. Wettability variation of surfaces with polyester or silica nanopa...

Watch this Scientific Journal Video about The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight at JoVE.com

The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

The overall goal of this methodology is to examine the changes in the surface of steel coatings prepared from polyester and silica nanoparticle coated-polyester after being exposed to sunlight. This method can help answer key questions in the industrial fields and areas such as nono coatings and anticorrosion. The main advantage of this technique is it provides a comprehensive understanding of the behavior of nano coatings exposed to weathering conditions.Demonstrating the procedure will be Jitraporn Vongsvivut and Vi Khanh Truong from our laboratories. First, rinse steel samples previously exposed to sunlight with double distilled water and then dry using nitrogen gas. Keep the samples in an airtight container to prevent any air contaminants absorbing onto the surface.Analyze the sample surface chemistry using attenuated total reflection infrared microspectroscopy, or ATRIR. First, open the cantilever of the ATR unit and load the sample on an aluminum disk into the ATR unit located on the microscope stage. Lift the sample stage of the ATR unit upwards and use the objective to focus on the sample surface.Press single image and add an annotation at the cross hair as center. Then make a larger overview image to cover the desired area on the sample surface by pressing image of large area. Move back to the center position.Next, lower the ATR sample stage, then close and tighten the cantilever of the ATR unit. On the background page, select measure background once and click next. On the next measurement page, select current position and click next.Rotate the manual pinhole wheel from open to 0.3, equivalent to a 3 micron diameter beam size and check the IR signal. Then measure the background by pressing measure background. Slowly lift the sample on the ATR sample stage upwards to make contact with the ATR crystal.Once observing bands on the live spectrum, draw a grid map on the area of interest in the visible image. Click next. After that, fill out the parameters including sample name and select the appropriate scan time and start the measurement by clicking measure sample.Once the scan is finished, click repeat. After saving the data, open the master file using the spectroscopy software. Choose the peak of interest on the IR spectra and right click on it.Under the integration tab, choose integration to create two-dimensional false color maps. To perform surface wetability measurements, place one of the samples on the stage of a contact angle goniometer equipped with a nanodispenser. Adjust the position of the micro syringe assembly so that the bottom of the needle appears about a fourth of the way down in the live video window screen.Now, raise the sample using the Z-axis until the distance between the sample and surface is about 5 milimeters. Lower the syringe until a droplet of double distilled water touches the surface. Then return the syringe to its original position.Press the run command to record the water droplet impacting on the surface for a 20 second period using a monochrome charged couple device, or CCD camera which is integrated with the hardware. Then press the stop command to acquire a series of images. Following this, press the contact angle command to measure the contact angles from the acquired images.To perform an optical profiling measurement, press the samples on the stage of the microscope. Focus on the surface using the 5x objective by controlling the Z-axis until the fringes appear on the screen. Press the auto command to optimize the intensity and then press the measurement command to initiate the scanning.Save the master files. Prior to statistical roughness analysis, press the remove tilt option to remove the surface waviness. Press the contour option to analyze the roughness parameters.Then click on the 3Di option to generate three-dimensional images of optical profiling files using compatible software. At this point, place the samples on steel disks and insert the steel disks into the magnetic holder of an atomic force microscope. Perform atomic force microscopy, or AFM scans, in tapping mode.Mechanically load a phosphorous doped silicon probe with a spring constant of 0.9 newtons per meter, a tip curvature with a radius of 8 nanometers, and a resonance frequency of approximately 20 kilohertz. Next, manually adjust the laser reflection on the cantilever. Then, choose the auto tune command and press the tune command to tune the AFM cantilever to reach the optimum resonance frequency reported by the manufacturer.Focus on the sample surface and move the AFM tips close to the surface. Then, click on the engage command to engage the AFM tips on the surface. Type 1 hertz into the scanning speed box.Choose the scanning areas and press the run command to perform the scan. Following this, choose the leveling option to process the resulting topographical data. Then, save the master files.Open the compatible AFM software and load one of the AFM master files. Press the leveling command to remove the tilting of surfaces and press the smoothing command to remove the background. Finally, press statistical parameters analysis to generate the statistical roughness.Water contact angle measurements demonstrated that wetability of the polyester coated substrata had not changed as a result of exposure to sunlight. After one year of exposure, the silica nanopartical polyester coated samples were 1.3 times greater in hydrophobicity than the unexposed samples. The XPS spectra indicated that iron was detected on the polyester coated substrata after one and five years of exposure and that there had been a slight decrease in the carbon content of the polyester coated samples after five years of exposure.No significant change was found in the silicon, iron and carbon levels in the silica nanoparticle polyester coated substrates. ATRIR showed that the number of carbonyl groups decreased on both the polyester and silica nanopartical polyester coated samples after five years of exposure. The microscale topographic evolution of the polyester and silica nanopartical polyester coated samples showed that the surfaces of both coatings became rougher than the original substrata after one year of exposure.The original silica nanopartical polyester coatings were smooth on a nanometer scale, however, after ultraviolet light exposure, both coatings were found to have formed globular structures and to exhibit a significantly higher average roughness than the original substrata. Once mastered, this set of techniques can be completed in the same day if its performed properly. While attempting these procedures its important to remember to keep the sample surfaces free from dust.Following this procedure, other methods like ATRIR can be used to answer other questions like what's the chemical distribution across the surface of the sample. After its development, this technique enabled researchers in the field of nanocoatings to explore the extent of polymer degradation. After watching this video, you should have a good understanding of how to operate instruments that are used in the characterization of a surface.Don't forget, that working with the instrumentation described in this protocol can be extremely dangerous. So always take precautions to protect yourself from hazards such as laser radiation or liquid nitrogen while performing this procedure.

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Research

JoVE Journal

Engineering

9.4K vistas.  Swinburne University of Technology. The overall goal of this methodology is to examine the changes in the surface of steel coatings prepared from polyester and silica nanoparticle coated-polyester after being exposed to sunlight. This method can help answer key questions in the industrial fields and areas such as nono coatings and anticorrosion. The main advantage of this technique is it provides a comprehensive understanding of the behavior of nano coatings exposed to weathering conditions.Demonstrating the procedure wi...