title: Assessment of roughness and chemical modification in determining the hydrophobic properties of metals

authors: Larmour, Iain A.

subjects: chemistry

abstract: “Etch and coat” methods, potentially useful for large scale production of superhydrophobic surfaces on metals, have been extended by introduction of a thin 20 nm Au interlayer which allowed thiol surface modifiers to be investigated. Fe, Ti and Zn surfaces modified in this way with a polyfluorothiol generally had lower contact angles, θ, than their silane modified equivalents but were more uniform and reproducible. The higher θ values for silanes appear to be associated with an increased effective roughness that is not seen in the thiol coatings, which follow the underlying surface. For Fe, Ti and Zn, θ increased to a maximum with etching time but then decreased significantly. Electron microscopy of samples etched for long times showed fewer grain boundaries, suggesting that the loss of hydrophobicity was related to reduced roughness. This was confirmed through quantitative measurements of roughness parameters which were directly correlated with the observed contact angles through the Wenzel equation. The observation of this behaviour for 3 different metals suggests it is a general effect and the assumption that increased etch times will give increased roughness is incorrect. Although etching , Au coating and thiol modification did not provide sufficient roughness for superhydrophobicity, electrodeposition of a Cu layer onto the metal substrates followed by electroless deposition of silver gave uniform surfaces with very high contact angles (up to θ = 168.9°) and low roll-off angles (α < 1°). This method is sufficiently simple and inexpensive to be suitable for application on industrial scales, for example in marine or aeronautical engineering.

text: Assessment of roughness and chemical modification in determining the hydrophobic properties of metals “Etch and coat” methods, potentially useful for large scale production of superhydrophobic surfaces on metals, have been extended by introduction of a thin 20 nm Au interlayer which allowed thiol surface modifiers to be investigated. Fe, Ti and Zn surfaces modified in this way with a polyfluorothiol generally had lower contact angles, θ, than their silane modified equivalents but were more uniform and reproducible. The higher θ values for silanes appear to be associated with an increased effective roughness that is not seen in the thiol coatings, which follow the underlying surface. For Fe, Ti and Zn, θ increased to a maximum with etching time but then decreased significantly. Electron microscopy of samples etched for long times showed fewer grain boundaries, suggesting that the loss of hydrophobicity was related to reduced roughness. This was confirmed through quantitative measurements of roughness parameters which were directly correlated with the observed contact angles through the Wenzel equation. The observation of this behaviour for 3 different metals suggests it is a general effect and the assumption that increased etch times will give increased roughness is incorrect. Although etching , Au coating and thiol modification did not provide sufficient roughness for superhydrophobicity, electrodeposition of a Cu layer onto the metal substrates followed by electroless deposition of silver gave uniform surfaces with very high contact angles (up to θ = 168.9°) and low roll-off angles (α < 1°). This method is sufficiently simple and inexpensive to be suitable for application on industrial scales, for example in marine or aeronautical engineering.

year: 2008

title: Revisiting Elton's copepods: lake construction has altered the distribution and composition of calanoid copepods in the British Isles

authors: Duggan, Ian C.

subjects: Science & Technology

abstract: It is now widely accepted that the construction of new lakes, ponds and reservoirs facilitates the invasion of non-indigenous aquatic species, due largely to low biotic resistance from native communities. The role played by constructed waters appears to be a particularly frequent feature of zooplankton invasions. Charles Elton, in his classic 1927 book “Animal Ecology”, noted that the estuarine calanoid copepod Eurytemora velox had invaded constructed inland waters in Britain and highlighted the lack of a key species, Eudiaptomus gracilis, in allowing its establishment. At the time, Elton’s observations were dismissed and his findings largely consigned to obscurity. Using occurrence records gathered since this time and current knowledge of calanoid copepod ecology and invasion biology, we re-examined the distributions of three species of freshwater calanoid copepods in the British Isles to: 1) determine the legacy of lake and pond construction on their distributions, and 2) reassess the conclusions made by Elton in light of this knowledge. The lack of natural lakes in the south and east of England, and the subsequent widespread development of new lakes and ponds, has altered calanoid copepod distributions. The common E. gracilis occurs frequently in the north and west of the British Isles in natural lakes, and is found in the south and east in constructed waters. The estuarine E. velox was found only in 3 natural freshwater sites, all in close proximity to the coast, but has been recorded in 23 constructed sites, many of these well inland. Elton noted a general lack of co-existence between E. velox and E. gracilis, with the relatively slow establishment rates of E. gracilis thought key in allowing the estuarine species to invade. However, subsequent collections suggest long-term cooccurrence of these species at some sites. We suggest that E. velox has now successfully invaded freshwaters in the British Isles. Eudiaptomus vulgaris is not known from natural lakes, but has been recorded in several constructed waters, and appears to have invaded Britain facilitated by lake construction. Current knowledge supports Elton’s contention that constructed waters are more readily invaded than natural waters, and that biotic resistance due to the presence of key species is important. While some specific criticisms of Elton’s ideas were valid, we argue that Elton’s concepts regarding constructed waters and invasions were in many ways correct and prescient of current understanding.

text: Revisiting Elton's copepods: lake construction has altered the distribution and composition of calanoid copepods in the British Isles It is now widely accepted that the construction of new lakes, ponds and reservoirs facilitates the invasion of non-indigenous aquatic species, due largely to low biotic resistance from native communities. The role played by constructed waters appears to be a particularly frequent feature of zooplankton invasions. Charles Elton, in his classic 1927 book “Animal Ecology”, noted that the estuarine calanoid copepod Eurytemora velox had invaded constructed inland waters in Britain and highlighted the lack of a key species, Eudiaptomus gracilis, in allowing its establishment. At the time, Elton’s observations were dismissed and his findings largely consigned to obscurity. Using occurrence records gathered since this time and current knowledge of calanoid copepod ecology and invasion biology, we re-examined the distributions of three species of freshwater calanoid copepods in the British Isles to: 1) determine the legacy of lake and pond construction on their distributions, and 2) reassess the conclusions made by Elton in light of this knowledge. The lack of natural lakes in the south and east of England, and the subsequent widespread development of new lakes and ponds, has altered calanoid copepod distributions. The common E. gracilis occurs frequently in the north and west of the British Isles in natural lakes, and is found in the south and east in constructed waters. The estuarine E. velox was found only in 3 natural freshwater sites, all in close proximity to the coast, but has been recorded in 23 constructed sites, many of these well inland. Elton noted a general lack of co-existence between E. velox and E. gracilis, with the relatively slow establishment rates of E. gracilis thought key in allowing the estuarine species to invade. However, subsequent collections suggest long-term cooccurrence of these species at some sites. We suggest that E. velox has now successfully invaded freshwaters in the British Isles. Eudiaptomus vulgaris is not known from natural lakes, but has been recorded in several constructed waters, and appears to have invaded Britain facilitated by lake construction. Current knowledge supports Elton’s contention that constructed waters are more readily invaded than natural waters, and that biotic resistance due to the presence of key species is important. While some specific criticisms of Elton’s ideas were valid, we argue that Elton’s concepts regarding constructed waters and invasions were in many ways correct and prescient of current understanding.

year: 2017

title: The Niupepa Collection: Opening the blinds on a window to the past

authors: Keegan, Te Taka Adrian Gregory

subjects: computer science

abstract: This paper describes the building of a digital library collection of historic newspapers. The newspapers (Niupepa in Maori), which were published in New Zealand during the period 1842 to 1933, form a unique historical record of the Maori language, and of events from an historical perspective. Images of these newspapers have been converted to digital form, electronic text extracted from these, and the collection is now being made available over the Internet as a part of the New Zealand Digital Library (NZDL) project at the University of Waikato.

text: The Niupepa Collection: Opening the blinds on a window to the past This paper describes the building of a digital library collection of historic newspapers. The newspapers (Niupepa in Maori), which were published in New Zealand during the period 1842 to 1933, form a unique historical record of the Maori language, and of events from an historical perspective. Images of these newspapers have been converted to digital form, electronic text extracted from these, and the collection is now being made available over the Internet as a part of the New Zealand Digital Library (NZDL) project at the University of Waikato.

year: 1999-12