Development of new methodologies for the study of surface tension and contact angle of drops in an electric field.

摘要

Understanding the influence of an electric field on surface properties of liquids is of importance from both fundamental and practical standpoints. Charged or electrified drops currently play a key role in various applications, ranging from microfluidic devices to agricultural treatments. Nevertheless, the effects of the electric field on surface properties of drops are not understood yet, mainly due to the lack of reliable tools and methodologies to measure such effects.; In this research, novel methodologies are developed that allow study of shape, surface tension, and contact angle of drops in the electric field: Automated Polynomial Fitting (APF) is a high-accuracy technique to determine contact angle of drops. It is applicable quite universally, and hence can be employed to measure the effect of the electric field on contact angles. Axisymmetric Drop Shape Analysis-Electric Fields (ADSA-EF) is a sophisticated drop-shape shape technique developed to study surface tension of drops in the electric field. ADSA-EF can also measure surface tensions in the absence of gravity; hence it is an ideal tool for microgravity research. Axisymmetric Liquid Fluid Interface-Electric Fields (ALFI-EF) is a side product of this research that can predict and simulate drop shapes in the electric field.; Extensive experimental work was performed using the new methodologies. The correlation between thermodynamic contact angles and the electric field was determined for the first time, using APF. It was found that contact angle of polar liquids increases in the electric field (depending on the size of the molecules), whereas non-polar liquids remain unaffected by the field. The observations were interpreted in terms of liquid interfacial tensions, using thermodynamic relations. ADSA-EF experiments showed similar increase in liquid surface tensions; furthermore, they revealed a second-order correlation between the surface tension of conducting liquids and the electric field.; In addition, two sets of ADSA-EF experiments were conducted in reduced-gravity using facilities provided by the Canadian Space Agency (CSA). In general, the measurements in the reduced-gravity condition agreed well with the previous ground-based measurements. The results suggested that gravity has no significant influence on the surface tension, as expected.