Precise drop dispensation on superhydrophobic surfaces using acoustic nebulization

Abstract

The adhesion forces of liquid drops on superhydrophobic surfaces are typically in the nano-Newton range which presents problems in their dispensation from pipettes. Furthermore, since the liquid adheres more strongly to the pipette tip, some portion of the liquid will tend to remain on the tip, causing inaccuracy in the volume dispensed. We advance a novel approach here, in which the spray from an acoustic nebulizer is sent to a superhydrophobic receptacle and the volume ascertained precisely using a weighing scale. The superhydrophobic surface was identified to develop via a galvanic displacement mechanism in an electroless deposition process. A time dependent morphology change from granular to dendritic with longer immersion into the silver nitrate solution was found which indicated that granular growth beyond a certain size was not feasible, although granular structures were more preferentially formed just after nucleation. The dendritic structure formation was likely due to the natural tendency of the process to maintain or increase the surface area to volume ratio in order not to limit the rate of deposition. An immersion for at least 7 seconds into the silver nitrate solution, when the granular structures were predominant, was all that was needed to ensure superhydrophobicity of the surfaces. Also, the superhydrophobic state required not just significant numbers of the granular structures to be present but also interrupted coverage on the surface. On using the technique, a single drop was created by subsequently covering the receptacle with a lid and shaking it gently. The volume dispensed was found to vary linearly with the operation time of the nebulizer. We elucidated the observed increased ability of drops to reside on inclines using wetting mechanics and presented an elementary mathematical description of the extent of aerosol coverage on the surface, which has implications for the mechanics of aerosol growth into drops. The structural changes in enhanced green fluorescent protein (EGFP) observed after acoustic dispensation necessitated all samples in a fluorimetric assay to involve equal nebulized volumes of the fluorescent protein marker for measurement consistency.

Liquid Body Formation from a Semispherical Superhydrophobic Well on a Small Incline

“…11,12,20 The introduction of a semispherical well on the SH surface presents a possible capacity to support additional hysteresis of the drop through the edges (of the well). The capability of edges to provide additional constraining on liquids has been harnessed in various applications.…”

SAW-based fluid atomization using mass-producible chip devices

“…3,5,8,18,19,21,26,30,31,37 The fluid then forms a meniscus around the tissue or capillary, which interacts with the SAW. 3,5,8,18,19,21,26,30,31,37 The fluid then forms a meniscus around the tissue or capillary, which interacts with the SAW.…”

Superhydrophobic Surfaces as a Tool for the Fabrication of Hierarchical Spherical Polymeric Carriers

“…The optical images of the obtained particles revealed the existence of two size populations for each condition. This may be explained by the overlapping of different droplets during spraying probably: 1) between the new arriving droplets and those already deposited on the SH surface and/or 2) due to high‐speed collision either in the midair or upon arrival to the SH surface, leading to an unavoidable fragmentation of larger droplets into smaller ones. Whatever the case, it was clear that by decreasing the polymer flow rate and increasing the air pressure inside the nozzle, the two‐size populations appeared to merge (Condition II), resulting in a narrow size distribution, which acquire an increased importance for cell and drug encapsulation purposes.…”