Abstract
The Rose window instability is a little-explored electrohydrodynamic instability that manifests when a layer of low-conducting oil is placed in an electric field generated by corona discharge in a point-to-plane configuration. Above a critical voltage, the instability starts as a single dimple in the oil layer right below the point electrode and subsequently evolves into a characteristic pattern of polygonal cells. In this study, we experimentally explore governing parameters that guide the instability and document geometric attributes of the characteristic cellular pattern. The driving force for the instability has been attributed to the buildup of charged ions which in turn apply an electric pressure on the oil surface. We confirm the charged surface distribution using thermal imaging and demonstrate that the instability can be locally inhibited by preventing charge buildup under an ion shadow.
Highlights
Controlled spreading of droplets and liquid films over a solid substrate has widespread use in applications such as coating, printing, micro- and bio-fluidics to name a few
We investigate the critical voltage at which the Rose window instability (RWI) manifests itself as a function of the pin height and liquid layer thickness
This trend is in accord with experimental results reported by Pérez [3], who attributed the instability to the electric pressure acting at the air–liquid interface
Summary
Controlled spreading of droplets and liquid films over a solid substrate has widespread use in applications such as coating, printing, micro- and bio-fluidics to name a few. It has been proposed that corona discharge can be an effective technique for controlled droplet spreading [1,2]. Corona discharge is effected by the ionization of air in the vicinity of a sharp-tipped conductor carrying a high voltage. The instability was nicknamed the Rose window instability (RWI) by Pérez [3], who first identified that it occurs only in low-conducting liquids. The RWI has been explored in more detail both experimentally and theoretically by only a handful of researchers. Vega & Pérez [4] used linear stability analysis to obtain a theoretical estimate
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