Recent advances using a surface embossing technique allow us to inexpensively impart micro-scale surface features on heat exchanger construction material, which we exploit to reduce condensate retention. The retention of condensate is important to the performance of heat exchangers in a broad range of air-cooling and dehumidification applications. We report a study of wetting behavior and drainage performance on a series of embossed surfaces with different micro-groove dimensions. Static contact angles, critical sliding angles, droplet aspect ratios, etc, are reported with detailed surface topographical information. Our results show that unless the spacing between grooves is very large (>100 µm), the parallel-grooved surface feature normally increases the apparent contact angle of a droplet on the surface. The micro-groove structure causes anisotropic wetting behavior of the droplets, and apparent contact angles measured by viewing along with the micro-grooves (θ⊥) were found to be larger than those measured from the other direction (θ‖) (by viewing perpendicular to the grooves). A consistent reduction of a critical sliding angle was observed on surfaces after embossing (the micro-grooves are aligned to be parallel with gravity). This may be due to contact line discontinuities and contact-line pinning induced by a groove structure of the surface. Water droplets exhibit an elongated shape along the micro-grooves, which is in contrast to the nearly circular base contour observed on an isotropic surface. Smaller groove spacing, larger depth and steeper sidewalls are observed to be favorable for drainage enhancement and recommended as design guidelines in the future.
Static secondary ion mass spectrometry was used to study the surface reactions and lateral distributions of fatty carboxylic acid molecules on sputter-deposited gold and aluminium surfaces, as well as commercial aluminium-magnesium alloy surfaces, cleaned using UV/ozone. Films were prepared by spin coating dilute solutions of stearic acid and lauric acid onto the above surfaces. These carboxylic acids were shown to react with the oxide formed on the aluminium and aluminum-magnesium alloy substrates to produce a deprotonated acid anion, stabilized by the formation of a magnesium soap on the aluminium-magnesium alloy surface. Secondary ion imaging of stearic acid films revealed the formation of C-type crystals. Copyright 2003 John Wiley & Sons, Ltd.
KEYWORDS:ToF-SIMS; carboxylic acids; aluminium-magnesium alloys; magnesium soap formation; C-type crystals Traditionally, mass spectrometry of organic molecules such as carboxylic acids has involved the introduction of the sample of interest into a heated ionization chamber, followed by the measurement of the mass to charge ratio using mass analysers such as quadrupoles, magnetic sector fields and time-of-flight tubes.1 The development of static secondary ion mass spectrometry by Benninghoven 2 has since allowed researchers to generate gas-phase ions from a solid surface containing species of high molecular mass, such as single layers of long-chain organic molecules held on a solid substrate.The study of organic molecules on surfaces using traditional instrumentation, such as x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), has not developed as rapidly as areas that are considered to be inorganic in nature, 3 such as the study of crystalline metal oxides. Progress in these areas has been hindered by the knowledge that organic thin films are often damaged by electron bombardment used for charge neutralization, they become unstable under high vacuum conditions or undergo charge shifting due to an electrically insulating nature. Techniques such as static SIMS and XPS have been used to confirm the damaged structures that arise when molecules of an organic film are subjected to severe x-ray or electron bombardment inside a spectrometer. Studies indicate that the damage induced is primarily due to photon-induced electrons that cause bond cleavage. 4 -6 Static SIMS, by contrast, uses a gentle ionization technique that can provide information about the surface chemistry of the outermost layers of a material while causing Ł Correspondence to: D. J. Miller, Surface Science Western, Western Science Centre, University of Western Ontario, London, Ontario, Canada N6A 5B7. E-mail: dmiller3@uwo.ca negligible surface damage. In general, static SIMS involves the use of mass spectrometry to measure the mass to charge ratio of secondary ions emitted from a solid surface when bombarded with a primary ion beam. The positively and negatively charged secondary ions emitted from the surface due to bombardment of the primary ion beam contain both elemental and m...
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