CONTACT ANGLE MEASUREMENTS BY SESSILE-DROP TECHNIQUE ON A VERTICAL SURFACE
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Данная работа представляет результаты измерения краевых углов методом сидячей капли на вертикаль-ной поверхности. каплю водной фазы с помощью шприца с иглой помещали на поверхность вертикального стеклянного стержня диаметром 2 мм, модифицированного кремнеземом (аэросил А-380) и гексиламином. Наблюдалось осаждение частиц кремнезема на поверхности стекла в результате контактной коагуляции. Формировался тонкий модифицирующий слой. каплю фотографировали, проводили касательные к профилю капли в верхней и нижней точках трехфазного контакта и непосредственно измеряли углы оттекания θCite
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Combining digital photography with AutoCAD and Proe,the parameters in surface tension measured by sessile drop method was determined.The results show that the method for calculating the surface tension has high accuracy,which can provide computer aid for adopting sessile drop method measuring high temperature metal surface tension.
Spinning drop method
Tension (geology)
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Abstract The effect of evaporation on the contact angle of a sessile drop of water on glass and polycarbonate substrates has been investigated. It has been observed that the contact radius depends on the initial mass of the drop and remains constant throughout the progress of evaporation. The evaporation rates in both systems are proportional to the contact radii of sessile drops. The contact angle, however, decreases as evaporation proceeds. In the case of water-glass system, the contact angle decreases almost linearly with time. On the other hand, in water-polycarbonate system, the contact angle shows a considerable departure from linearity. It has been shown that the non-linear behavior of contact angle becomes more pronounced with increasing initial contact angle. Keywords:
Polycarbonate
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Hysteresis
Pressure angle
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The basic principle of measuring spreading coefficients by the large sessile drop method has been introduced.The spreading coefficients of some liquids on the paraffin and gelatin film were measured.The results show that the contact angles calculated from spreading coefficients are equal to the measured volues.The surfactants often can improve the wetting behavior.
Solid surface
Gelatin
Wetting transition
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Abstract In the last decades, many attempts have been made to investigate influence quantities on the formation of contact angles and their interpretation. The effect of gravitation on the measured contact angles is a controversially discussed mater. In 1876 J. W. Gibbs already formulated conditions for equilibrium and therefore even for the equilibrium contact angle θ e which describe the acting gravitational field on a fluid component. Nevertheless, these relations often are not considered. The presented study illustrates differences between the apparent contact angles of sessile drops which are obtained by dynamical measurements with the inclined-plate and the needle-in method. This fact demonstrates that the force distibution at the triple line additionally differs in dependence on the used measuring method. The force distribution at the triple line depends on the relative position in the gravitational field (e.g. inclined or horizontal sample position) and on the curvature of the liquid-vapour interface (interfacial tension). Hence, theses effects on the apparent contact angles have to be considered for a reasonable interpretation of the measurement data. For this purpose, an approach to describe the effect of forces related to gravity effects on contact angles will be presented.
Position (finance)
Line (geometry)
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Goniometer
Wetting transition
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Gravity-induced sagging can amplify variations in goniometric measurements of the contact angles of sessile drops on super-liquid-repellent surfaces. The very large value of the effective contact angle leads to increased optical noise in the drop profile near the solid-liquid free surface and the progressive failure of simple geometric approximations. We demonstrate a systematic approach to determining the effective contact angle of drops on super-repellent surfaces. We use a perturbation solution of the Bashforth-Adams equation to estimate the contact angles of sessile drops of water, ethylene glycol, and diiodomethane on an omniphobic surface using direct measurements of the maximum drop width and height. The results and analysis can be represented in terms of a dimensionless Bond number that depends on the maximum drop width and the capillary length of the liquid to quantify the extent of gravity-induced sagging. Finally, we illustrate the inherent sensitivity of goniometric contact angle measurement techniques to drop dimensions as the apparent contact angle approaches 180°.
Goniometer
Dimensionless quantity
Diiodomethane
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