Surface texturing has emerged as a transformative approach to improving friction, lubrication, and wear across a wide range of mechanical components [...]

Accumulation of soils and other particulate matter on the front cover glass of solar photovoltaic (PV) modules results in transmission losses that detrimentally affect the power output of PV installations. Cementation reactions, which occurs due to interactions between the dust and the glass surface in the presence of temperature, humidity, and pH, results in the dust becoming rigidly attached and potentially difficult to remove with conventional cleaning methods. In this study, accelerated soiling and cementation tests on glass coupons have been performed using a custom instrumented soiling chamber and several standardized soils (Arizona Test Dust, ARAMCO Test Dust, and China Test Dust) to assess soil adhesion and cementation behaviors. Micromechanical scratch testing, along with supporting water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) measurements are used to characterize the surface chemistry of the soiled coupons and surface energy evolution of the deposited soils before and after cementation. The end result of this study is a better understanding of the surface properties of cemented soils, which can potentially lead to the development of novel soiling mitigation technologies for PV applications.

The friction behavior of core-shell nanostructure textured surfaces (CSNTSs) was systematically studied using indenters of various tip radii under several normal loads. The effects of the test parameters were investigated on two shell materials to elucidate friction mechanisms. The test parameters, material type, texture uniformity, and deformation had a significant impact on friction values. At the lowest load, adhesion led to the highest coefficient of friction (COF) on both surfaces for all tip sizes tested. At low contact pressures, the Al/diamond-like carbon (DLC) CSNTS experienced a lower COF than the Al/amorphous silicon (a-Si) CSNTS due to DLC has better tribological property than a-Si. At higher contact pressures, more severe deformation and thus higher COF occurred on the Al/DLC CSNTS.

Characterization of photovoltaic (PV) module materials throughout different stages of service life is crucial to understanding and improving the durability of these materials. Currently the large-scale of PV modules (>1 m2) is imbalanced with the small-scale of most materials characterization tools (≤1 cm2). Furthermore, understanding degradation mechanisms often requires a combination of multiple characterization techniques. Here, we present adaptations of three standard materials characterization techniques to enable mapping characterization over moderate sample areas (≥25 cm2). Contact angle, ellipsometry, and UV-vis spectroscopy are each adapted and demonstrated on two representative samples: a commercial multifunctional coating for PV glass and an oxide combinatorial sample library. Best practices are discussed for adapting characterization techniques for large-area mapping and combining mapping information from multiple techniques.

When dust and other particulates accumulate on the surface of solar modules, the power output of these soiled modules is significantly reduced. To combat this issue, antisoiling coatings can be placed on the top glass surface of solar modules. While there exists some understanding of how antisoiling coatings reduce soiling and reflection losses, approaches to characterize the durability and stability of the chemistry and morphology of antisoiling PV glass module coatings and how they evolve in response to soiling interactions are currently underdeveloped. Here we present the use of small-angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) as a methodology for studying the morphology and chemistry of pristine and soiled antisoiling coatings. This work demonstrates the effectiveness of SAXS in observing coating morphology despite the presence of soil surface layers-a capability which sets it apart as a strong characterization tool for antisoiling coatings on PV glass. XPS and XAS are used as complementary techniques to characterize the evolution of coating surface chemistry before and after soiling. XAS is shown to detect subtle chemical changes in the coating surface that cannot be detected by XPS.

The number of revision joint replacements has been increasing substantially over the last few years. Understanding their failure mechanism is extremely important for improving the design and material selection of current implants. This study includes ten retrieved and four new mildly cross-linked ultra-high molecular weight polyethylene (UHMWPE) acetabular liners. Among them, most of the prostheses (n = 5) were reported to be revised and replaced due to aseptic loosening, followed by painful joint (n = 2), dislocation (n = 1), intra articular ossification (n = 1), combination of wear (liner) and osteolysis (stem) (n=1). Surface deviations (wear, material inflation and roughness), oxidative degradation and change of material properties were measured using micro-computed tomography (micro-CT) scan, 3D laser scanning microscopy, raman spectroscopy and nanoindentation, respectively. Prostheses having eccentric worn areas had much higher linear wear rates (228.01 ± 35.51µm/year) compared to that of centrically worn prostheses (96.71 ± 10.83µm/year). Oxidation index (OI) showed similar trends to the surface penetration depth. Among them, sample 10 exhibited the highest OI across the contact area and the rim of the cup liner. It also had the lowest hardness/elasticity ratio. Overall, wear and creep, oxidative degradation and reduced hardness/elasticity ratio all contributed to the premature failure of the UHMWPE acetabular cup liners.

When dust and other particulates accumulate on the surface of solar modules, the efficiency of these soiled modules is significantly reduced. Soiling is especially problematic in regions with little rain, where water resources for cleaning modules are scarce. To combat this issue, anti-soiling coatings, on the top-surface of solar modules, are beginning to enter the market. However, limited understanding of anti-soiling mechanisms and uncertainty in their durability has limited their deployment. Porous coatings are anticipated to discourage soiling because their rough surfaces reduce the strength and probability of dirt-to-coating bonds. However, the evolution of this morphology through soiling cycles is largely unknown. Here we present the use of small angle X-ray scattering (SAXS) to monitor the morphology of pristine and soiled, industry-sourced coatings. Initial soiling tests are performed using a standardized soil (AZ road dust) in the lab. This work demonstrates the effectiveness of SAXS in monitoring coating morphology despite the presence of soil surface layers. The capability of SAXS studies to be performed under various temperature, humidity, and soiling conditions sets it apart as a strong characterization tool for developing the understanding of functionality and degradation mechanisms of anti-soiling coatings for PV glass.

Nanotextured surfaces can effectively reduce friction and adhesion, especially in applications with micro-and nanoscale contact interactions. However, for these surfaces, a common weakness is a lack of structural integrity of the individual nanotextures when subjected to contact loading, resulting in permanent deformation at even the moderate contact forces encountered in microscale systems. Nanostructure-textured surfaces (NSTSs), composed of arrays of novel Al/a-Si core-shell nanostructures (CSNs), have been developed with a desirable combination of low friction and high deformation resistance. When subjected to nanoscratch testing, these surfaces are shown to have extremely low coefficients of friction (as low as similar to 0.015), as well as no detectable nanostructure deformation at contact forces up to 8,000 mu N (estimated contact pressure greater than 1 GPa). In addition, the NSTSs have low adhesion (pull-off) forces on the order of less than 1 mu N. The unique properties of these NSTSs provide avenues for designing low-friction, deformation-resistant surfaces that could benefit a variety of fields, including micro/nanoelectromechanical systems (MEMS/NEMS), microelectronics, magnetic recording, or any other application where the mechanical integrity of nanostructures is important.

Nanostructure-textured surfaces can reduce friction and adhesion of micro-and nano-electromechanical systems (MEMS/NEMS). For MEMS/NEMS incorporating moving parts, the fatigue properties of nanostructures pose a challenge to their reliability in long-term applications. In this study, the fatigue behavior of hemispherical Al/a-Si core-shell nanostructures (CSNs), bare hemispherical Al nanodots, and a flat Al/a-Si layered thin film have been studied using nanoindentation and nano-scale dynamic mechanical analysis (DMA) techniques. Fatigue testing with nano-scale DMA shows that the deformation resistance of CSNs persists through 5.0 x 10(4) loading cycles at estimated contact pressures greater than 20 GPa. For bare Al nanodots which lack the hard a-Si shell, significant nanostructure deformation results due to repeated cyclic loading. In addition, for the Al/a-Si layered thin film which lacks the geometric and dislocation confinement properties of CSNs, cyclic loading results in fatigue failure of the a-Si layer. Even at elevated contact pressures, CSNs demonstrate none of the failure mechanisms exhibited by the other two control structures. The unique properties displayed by CSNs when subjected to fatigue testing establish their prolonged reliability and durability when implemented in micro-and nano-scale applications.

Six types of diamond-like carbon (DLC) coatings with zirconium (Zr)-containing interlayers on titanium alloy (Ti-6Al-4V) were investigated for improving the biotribological performance of orthopedic implants. The coatings consist of three layers: above the substrate a layer stack of 32 alternating Zr and ZrN sublayers (Zr:ZrN), followed by a layer comprised of Zr and DLC (Zr:DLC), and finally a N-doped DLC layer. The Zr:ZrN layer is designed for increasing load carrying capacity and corrosion resistance; the Zr:DLC layer is for gradual transition of stress, thus enhancing layer adhesion; and the N-doped DLC layer is for decreasing friction, squeaking noises and wear. Biotribological experiments were performed in simulated body fluid employing a ball-on-disc contact with a Si3N4 ball and a rotational oscillating motion to mimic hip motion in terms of gait angle, dynamic contact pressures, speed and body temperature. The results showed that the Zr:DLC layer has a substantial influence on eliminating delamination of the DLC from the substrates. The DLC/Si3N4 pairs significantly reduced friction coefficient, squeaking noise and wear of both the Si3N4 balls and the discs compared to those of the Ti-6Al-4V/Si3N4 pair after testing for a duration that is equivalent to one year of hip motion in vivo.

Without antireflective coating, more than 4% of incident light is reflected from the standard front cover glass of photovoltaic (PV) modules. Module efficiency is one of the largest levers to impact the cost-per-watt of solar and recovering some of this reflected light with a simple anti-reflective coating (ARC) has become widespread. The types of ARC can vary in deposition method (roll coating, spray coating, sputtering, etc.) as well as composition and performance. The most widely adopted coatings today are based on a porous silica film with a thickness optimized for the solar spectrum. Current coatings, however, have room for improvement in both the performance and cost which means that manufacturers are actively looking for new solutions that drive down the levelized cost of electricity (LCOE). In this work, we report the test results for a new AR coating from WattGlass showing significantly improved optical performance compared to the traditional AR coatings. The new coating takes advantage of water-based chemistry that is more environmentally friendly than the sol-gel processes used in standard production coatings. This chemistry allows a high performance and durable coating to be deposited and cured at room temperature and is compatible with industry standard glass tempering conditions. The samples under test in this work were subjected to extensive optical performance testing at material and mini-module level. Our results show increased optical performance for the new coating, with solar weighted transmittance improvements as high as 3.1%. This increased optical performance directly translates to increased energy yield, lower LCOE and reduced warranty costs.

The nanoindentation behavior of hemispherical Al/a-Si core-shell nanostructures (CSNs), horizontally-aligned Al/a-Si core-shell nanorods (CSRs) with various lengths, and an Al/a-Si layered thin film has been studied to understand the effects of geometrical confinement of the Al core on the CSN deformation behavior. When loaded beyond the elastic limit, the CSNs have an unconventional load-displacement behavior with no residual displacement after unloading, resulting in no net shape change after indentation. This behavior is enabled by dislocation activities within the confined Al core, as indicated by discontinuous indentation signatures (load-drops and load-jumps) observed in the load-displacement data. When the geometrical confinement of the core is slightly reduced, as in the case of CSRs with the shortest rod length, the discontinuous indentation signatures and deformation resistance are heavily reduced. Further decreases in core confinement result in conventional nanoindentation behavior, regardless of geometry. Supporting molecular dynamics simulations show that dislocations nucleated in the core of a CSN are more effectively removed during unloading compared to CSRs, which supports the hypothesis that the unique deformation resistance of Al/a-Si CSNs are enabled by 3-dimensional confinement of the Al core. (C) 2017 Elsevier B.V. All rights reserved.

The mechanical behavior of novel Al/a-Si core-shell nanostructures (CSNs) is studied using instrumented nanoindentation to investigate the role that the confined core volume plays on the mechanical response of these structures. The CSNs are fabricated from truncated hemispherical Al nanodots with 100, 200, and 300 nm base diameters, which are then conformably coated with a-Si. CSNs with the smallest core diameter, and therefore the smallest confined core volume, have a unique load-displacement behavior characterized by nearly complete recovery of deformation beyond the elastic limit, which is enabled by dislocation activities within the confined Al core. In conjunction with this deformation recovery, discontinuous indentation signatures known as "load-drops" and "load-jumps" are observed during loading and unloading, respectively. As the size of the confined core volume increases, these indentation signatures are suppressed and the deformation-resistant properties are reduced. Supporting molecular dynamics simulations show that a smaller core volume results in a larger back-stress developed in the core during indentation, which further correlates with improved dislocation removal from the core after unloading. This complementary experimental and modeling investigation provides insight into the mechanisms that contribute to the unique mechanical properties of Al/a-Si CSNs. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The effects of using polydopamine (PDA) coated Cu nanoparticles (PDA-Cu) as a filler in the polytetrafluoroethylene (PTFE) topcoat of a PDA/PTFE dual-layer coating are investigated, where the PDA is used as an adhesive basecoat. Tribological tests show that the addition of PDA-Cu in PTFE increases the wear life of PDA/PTFE by a factor of two, approximately three orders of magnitude greater than that of pure PTFE without a PDA basecoat. This increase in wear life is achieved without compromising the low coefficient of friction characteristic of pure PTFE. Scratch tests show that the PDA-Cu filler improves adhesion between the PTFE and the PDA, preventing large scale delamination and also increases the toughness of the coating, preventing ruptures at lower loads.

This investigation examines the effects of incorporating graphite as a filler in the polytetrafluoroethylene (PTFE) topcoat of a polydopamine/PTFE dual-layer coating. Polydopamine (PDA) is used to enhance the adhesion of PTFE coatings to the substrate, and graphite is used to improve the formation of a transfer film on the counterface and to take advantage of the low-friction properties of graphite. The results show that incorporating only 1.0 wt% graphite in PDA/PTFE coatings can increase their durability fivefold and reduce friction by 17 %. Examination of the wear morphology indicates that these improvements in tribological properties are in fact the result of the formation of a transfer film on the counterface that allows the coating to essentially slide against itself, creating a low shear strength interface that exhibits exceptionally low friction and low wear. Linearly increasing load scratch tests show that the improvement in durability is also the result of improved adhesion between the PTFE topcoat and the PDA basecoat, preventing large-scale delamination of the coating.

We report a method of producing superhydrophilic surfaces on titanium substrates via sandblasting and dip-coating with colloidal silica nanoparticles. The surface exhibits a high level of hydrophilic stability, as it stays superhydrophilic for an excess of 40days and through multiple wetting-dewetting cycles. The combination of microscale roughness from the sandblasting and nanoscale roughness from the silica particles results in a micro-nano binary structure, which greatly enhances the hydrophilicity of the titanium samples. Due to the simplicity and ease of implementation of this method, such a surface is suitable for potential use in a variety of applications, such as prosthetic dentistry and other biomedical fields.

We report the fabrication of stable superhydrophilic and superhydrophobic surfaces on titanium substrates using simple methods. Sandblasting the titanium surface to generate microscale roughness, followed by dip-coating in a colloidal silica nanoparticle solution to generate nanoscale roughness and a hydrophilic surface chemistry, produces a superhydrophilic surface. Further chemical modification with a several-nanometer-thick low surface energy fluorinated carbon film renders the surface superhydrophobic. The wettability of these superhydrophilic and superhydrophobic surfaces display a high degree of stability, as both surfaces retain their wetting properties for at least 54 days under multiple wetting/de-wetting cycles. Furthermore, the superhydrophilic surfaces retain their wetting properties in excess of 25 months after storage in ambient atmosphere. Due to their long-term wetting stability and ease of fabrication, these surfaces have potential applications in a variety of fields, including biomedical fields where titanium is widely used. (C) 2013 Elsevier B.V. All rights reserved.

Self-cleaning and antifogging coatings are of great interest for application in outdoor solar cell installations to mitigate the performance loss and associated maintenance costs due to environmental contamination. These coatings, applied to the cover glass of solar panels, can remove contaminants when wetted with rain water and transmit more sunlight in foggy weather. Herein, we report a superhydrophilic silica nanoparticle film that exhibits the self-cleaning effect without relying on photocatalytic materials. When wetted with simulated light raining conditions, the coated glass removed 90% of surface contaminants, compared to only 48% removed from the bare glass. The deposited film created an antifogging surface in addition to increasing the solar transmittance (AM 1.5) of glass substrates by 4.3% over bare glass in the wavelength range of 350–1100nm.

A nanoindentation study was performed on a novel type of core–shell nanostructure (CSN) that consists of a nanostructured core layer covered by a nanoscale shell layer. The CSNs were formed by first depositing an Al film with protruding nanostructures onto a smooth Si surface through thermal evaporation and then depositing an amorphous Si film by plasma-enhanced chemical vapor deposition on top of the Al layer. It was found that these CSNs have very high yield strength of about 19GPa. They can also sustain about 23% engineering strain without fracture. Furthermore, these CSNs show complete recovery of plastic deformation upon repetitive nanoindentation. Such a novel type of CSN should find applications in many areas, including nanodot-based magnetic recording, nanoimprinting lithography, microelectromechanical systems, surface wetting and biomedicine, where mechanical integrity of the nanostructures is of paramount importance.