The growth rate of infinitesimal perturbations in electrified jets exhibits different behavior at the viscid and inviscid limits. Using Saville's approach to estimate the growth rate for perturbations in the longwavelength limit and by ignoring the effects of gravity, we derive two scaling laws for the jet breakup length in two regimes of the Taylor-cone mode. Our experimental measurements show clear dependency of the jet length on the flow rate; however, change of the applied voltage appears to affect only the cone angle but not the jet itself. The experimental data agree excellently with our theoretical model in both cases. On the basis of the jet diameter, the transition between viscid and inviscid limits appears to occur at an electric Reynolds number of approximately 5. Finally, we show how to enhance the quality and the resolution in electrostatic-inkjet-printing applications by setting the printing distance less than the jet length and predict the line width as a function of the operational parameters.

The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validated.

Whether an electrified jet breaks up whilst the jet maintains a straight line (varicose), or alternatively the jet trajectory becomes chaotic (whipping), depends on the competition of the interfacial forces. Starting from the competition of normal stresses on the jet surface, we derive scaling laws in different electro-hydrodynamic operating regimes as a function of fluid properties and the flow rate. The onset of whipping occurs when this scaling function reaches a threshold, which is independent of the electric field strength. However, experimental evidence indicates that this onset condition applies only when the viscosity and electrical conductivity of a liquid are small enough. As a result, we further introduce a general parameter to incorporate viscous effects into the scaling law. A unified threshold value for this parameter is found through a substantial number of experiments for liquids having a wide range of properties, and under a wide variety of operational conditions of flow rate.

The methods to study capillary waves have been reviewed, together with the emerging practical applications of theirs and new theoretical developments in the field. The focus is on monochromatic ripples of frequency in the range 0.1-10 kHz. A capillary wave apparatus has been constructed that combines several recent advances on the technique. It is based on profilometry of waves decaying with distance, with a highspeed video camera detecting light refracted by the surface. A code to process the images has been developed that executes a regression analysis to determine the characteristics of the wave. High precision and accuracy have been achieved: standard deviation from the mean of ±0.5% for the wavelength and ±7% for the decay length; mean deviations from the theoretical values ±0.2% for the wavelength and ±5% for the decay length. An analytic approximation for the dispersion relation has been used to determine the Gibbs elasticity of a surfactant monolayer from the data for decay length vs. frequency. The elasticity of an octanol monolayer has been determined with precision of ±1 mN/m, in excellent agreement with the theoretical value. Surface tension can be measured from the wavelength data with precision of ±0.3 mN/m. It has been demonstrated that the effect of the surface elasticity on the wavelength is significant and accurate wavelength data can actually be used to determine the elasticity if the surface tension is known.