Tami Lasseter Clare

Surfactant-free hybridization of transition metal oxide nanoparticles with conductive graphene for high-performance supercapacitor

In order to improve specific capacitance and limit electrical resistance, high-quality exfoliated graphene decorated with transition metal (Fe, Mn, Co) oxide nanoparticles (NPs) has been successfully synthesized without the use of surfactantvia a simple, general, environmentally-friendly chemical process. The specific capacitance of as-prepared graphene/Mn3O4 composite reach 239.6 F/g, when employed as the anode material in neutral NaCl electrolyte solutions (cf. 98.2 F/g for pristine graphene and 141.4 F/g for pure Mn3O4 NPs), which indicate the synergetic effects from both graphene and attached Mn3O4 NPs. Moreover, the high conductivity of graphene eliminates the need for conductive carbon black as fillers. The current density of graphene/Mn3O4 reached as high as 4.5 A g−1 which is much higher than that of graphene oxide (GO) or reduced GO-based composites. This significant enhancement of capacitance and current density was attributed to the surfactant-free approach to hybridize graphene with transition metal oxide NPs, the excellent conductivity of pristine graphene combined with its large surface area, as well as a uniform distribution of NPs on the clean surface of conductive graphene. Thus the low-toxicity, inexpensive graphene-based hybrids show promising utility as high current density electrode materials for supercapacitor applications.

ON THE PROTECTIVE NATURE OF WAX COATINGS FOR CULTURALLY SIGNIFICANT OUTDOOR METALWORKS: MICROSTRUCTURAL FLAWS, OXIDATIVE CHANGES, AND BARRIER PROPERTIES

Abstract Changes in chemical, microstructural, and barrier properties of two commonly used and commercially available waxes – a microcrystalline wax (Renaissance wax) and a microcrystalline and carnauba blended wax (Butchers Boston Polish Amber Paste Wax) – for the prevention of corrosion on outdoor metalwork were investigated. The waxes were applied to both plain and patinated substrates of bronze and steel, and properties of the films were measured before and after weathering. Accelerated weathering was performed by accelerated UV-B illumination/condensation and outdoor weathering under standard South Florida exposures and in Portland, OR. Comparison of Fourier transformed micro-infrared and nuclear magnetic resonance spectra enabled characterization of chemical functional groups of these waxes as they weathered and showed relative increases in methylene character suggestive of cross-linking, appearance of terminal vinyl bands suggestive of chain-scission, and evidence of oxidative film damage. After annealing, microstructural changes were observed by thin-film X-ray diffraction and showed a decrease in crystallinity, which indicates a decrease in barrier properties. The barrier properties of the wax films after weathering were studied by electrochemical impedance spectroscopy and equivalent electrical circuits provided insights into the physical state of the films. The electrochemical impedance spectroscopy data showed that the permittivity of the weathered waxed panels increased, which was observed as a decrease in coating resistance and an increase in coating capacitance. Photographic documentation of the substrates showed extensive visible corrosion upon weathering. Our results demonstrate that waxed metal panels exposed outdoors do not have a period of stability when the protective qualities of the film do not change. This suggests that while waxes are commonly used to protect against corrosion, their barrier properties are affected by flaws in the microstructure and their susceptibility to chemical alteration during weathering. Results from a blind study with professional conservators as the participants are presented, to elucidate how they rank the importance of such factors as gloss and working lifetime when selecting protective coatings.

Characterization of High Performance Protective Coatings for Use on Culturally Significant Works

Protective coatings are commonly used to protect culturally significant works, such as outdoor sculptures and architectural elements. While the cost of damage due to corrosion is much higher than that of more common coating applications, the same types of protective coatings are used. Coatings having both chemical and physical intelligence that may offer superior weatherability and act as better barriers to water absorption than commonly used materials, such as waxes and acrylics, are investigated. Our findings indicate that the use of waterborne resins containing polyvinylidene fluoride with nanoclays of Laponite significantly improved performance and may be a viable option in the protection of material cultural heritage.

Minimizing Corrosion of Outdoor Metalworks Using Dispersed Chemically Stabilized Nanoclays in Polyvinylidene Fluoride Latex Coatings

Nanoclays are small enough to appear optically transparent, yet they have large surface-to-volume and high aspect ratios that can significantly inhibit water diffusion when incorporated into protective coatings. Clear coatings, which minimally affect the aesthetics of metalworks, are commonly applied to outdoor metalworks, such as sculptures, to prevent and slow corrosion. In recent years, waterborne clear coatings, rather than solvent-based clear coatings, are increasingly used in many applications to reduce the quantity of volatile organic components in the formulation, yet the performance of dry films produced from waterborne colloidal suspensions is generally poorer. In this work, we aim to improve the barrier properties of a highly weatherable waterborne acrylic/polyvinylidene fluoride emulsion by adding a synthetic nanoclay, Laponite, into the formulation. To improve clay–polymer compatibility, the clay was covalently modified using an acetoxy or perfluoroalkyl silane monomer that is reactive with the hydroxyl groups at the edges of the Laponite platelets. Cation exchange on the clay faces using phosphorylcholine was conducted to increase the stability in water and characterized by zeta potential. Resulting changes in barrier properties of the polymer nanocomposite films were characterized by gravimetry, colorimetry, and electrochemical impedance spectroscopy. Surface ablation after accelerated artificial weathering was monitored by attenuated total internal reflectance Fourier transform infrared microspectroscopy and Raman microspectroscopy, thin film X-ray diffraction (TF-XRD) and gloss and thickness measurements. The composite films showed many improved properties: reduced water sensitivity and ultraviolet-induced polymer degradation, which increased the barrier properties and reduced the diffusion constants over both short- and long-term weathering studies compared with films without nanoclays. The diffusion constant measured for the highest performing composite film showed that the performance gap between relevant water- and solvent-borne coatings used to protect outdoor metals was narrowed by half.