The Effect of Residual Abrasives on the Wettability of Polished Gold Surfaces

Abstract

When gold surfaces are prepared by polishing with alumina abrasives, the contact angles of water on these surfaces are found to be 34r-56°, even after some of the surface has been removed by etching with aqua regia. Reflection electron diffraction patterns on these surfaces show evidence of residual abrasive material on the surface which is not removed by etching. Gold that is smoothed by compression between smooth surfaces of aluminum, stainless steel, or mica shows water contact angles in the same range of values, with electron diffraction patterns showing the presence of alumina, iron oxide, and muscovite, respectively, on the surfaces. When gold surfaces are prepared by vacuum evaporation of high-purity metal on silica substrates or by polishing of gold with diamond abrasive followed by firing in oxygen at 1000°, the contact angles of water on these surfaces are 55-65°. The electron diffraction patterns show no contaminating oxide material. These results show that the presence of hydrophilic inorganic contaminants on surfaces can affect wettabilities as seriously (but in the opposite direction) as the more commonly discussed contamination by hydrophobic organic material.

The influence of environment on the drop size ? contact angle relationship

“…Later White and Drobek [13] stated that the presence of inorganic impurities such as alumina polishing agents made the surface more hydrophilic. By preparing the surfaces using diamond paste or vacuum evaporation with subsequent heating in oxygen, the resultant surface was observed to be hydrophobic.…”

“…He measured contact angles of 65 ~ and 80 ~ for water on gold and silver surfaces respectively. Plaksin and Bessonov [15] (52 o _ 78 o), White and Drobek [13] (55 ~ -65 ~ and Erb [14] (62.6 ~ + 3.4 o) have all reported hydrophobic behavior when measuring contact angles of water on gold and silver surfaces, at atmospheric pressure in equilibrium with water vapor. In contrast it appears that other workers Bewig and Zisman [16,17], Schrader [18,19], Bernett and Zisman [20], Gardner and Woods [21], Smith [22] and Gaines [23] have demonstrated gold surfaces to be hydrophilic in nature; the angle being zero at all pressures.…”

Oxidation of gold by ultraviolet light and ozone at 25 °C

“…In general, polar ͑such as metal oxides͒ surfaces are hydrophilic with water contact angles of 0°, and nonpolar surfaces are more hydrophilic with water contact angles greater than 0°. [29][30][31][32][33][34] With surface preparation and cleanliness a major problem in contact angle measurements, Schrader developed a vapor phase transfer ultrahigh vacuum method of determining contact angles in 1968 and extended this work to include the water contact angles on polished gold disks and evaporated gold films. 28 In 1964 White reported a water contact angle on gold of 60°Ϯ5°.…”

Efficacy of Cathodically Electro-Cleaning Nickel Thin Film Nozzle Plate for Piezo Inkjet Printer Head*

“…26) Ni(OH) 2 probably forms by a solid state process involving nucleation and growth. In some alkaline conditions, particularly concentrated solutions at high temperatures, films of [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] A thickness are formed at 90 C. 11,15,24,25) Therefore, the surface of an alkaline cleaned nickel nozzle plate is rendered into a ''known'' condition. Particulate dirt is usually removed together with the grease which binds it.…”