The precise and accurate production of millimetric water droplets using a superhydrophobic generating apparatus

Abstract

The production of millimetric liquid droplets has importance in a wide range of applications both in the laboratory and industrially. As such, much effort has been put forth to devise methods to generate these droplets on command in a manner which results in high diameter accuracy and precision, welldefined trajectories followed by successive droplets and low oscillations in droplet shape throughout their descents. None of the currently employed methods of millimetric droplet generation described in the literature adequately addresses all of these desired droplet characteristics. The reported methods invariably involve the cohesive separation of the desired volume of liquid from the bulk supply in the same step that separates the single droplet from the solid generator. We have devised a droplet generation device which separates the desired volume of liquid within a tee-apparatus in a step prior to the generation of the droplet which has yielded both high accuracy and precision of the diameters of the final droplets produced. Further, we have engineered a generating tip with extreme antiwetting properties which has resulted in reduced adhesion forces between the liquid droplet and the solid tip. This has yielded the ability to produce droplets of low mass without necessitating different diameter generating tips or the addition of surfactants to the liquid, well-defined droplet trajectories, and low oscillations in droplet volume. The trajectories and oscillations of the droplets produced have been assessed and presented quantitatively in a manner that has been lacking in the current literature.

Mesenchymal stromal cell encapsulation in uniform chitosan beads using microchannel emulsification

“…The microchannel surface should be as hydrophobic as possible to maximize oil phase wetting to promote droplet formation 23, 29 . As expected 30 , the hydrophobic pristine PTFE plates used to fabricate the had water contact angles above 90° (advancing water contact angle of θ A = 97 ± 1°; receding water contact angle of θ R = 43 ± 12°). The laser irradiation process results in a hierarchical topography consisting of a rippled microstructure that is superimposed by porous, wiry nanostructures ( Figure 3.A, B ).…”

“…The microchannel surface should be as hydrophobic as possible to maximize oil phase wetting to promote droplet formation 23,29 . As expected 30 , the hydrophobic pristine PTFE plates used to fabricate the had water contact angles above 90° (advancing water contact angle of 𝜃 𝐴 = 97 ± 1°; receding water contact angle of 𝜃 𝑅 = 43 ± 12°).…”

On the Oblique Impact Dynamics of Drops on Superhydrophobic Surfaces. Part II: Restitution Coefficient and Contact Time

“…A drop-on-demand (DOD) generator provides monodisperse droplets that fall downward onto the sample as it moves. For full details on this device, see Wood et al 25 Synchronization between the pneumatic accelerator and the DOD was accomplished using an Arduino MEGA 2560 microcontroller prototyping board (Arduino Company). Impact events were recorded by a Photron SA5 highspeed camera, fitted with a Navitar Macro Zoom 7000 lens.…”

On the Oblique Impact Dynamics of Drops on Superhydrophobic Surfaces. Part I: Sliding Length and Maximum Spreading Diameter

“…Water droplets were produced by a drop-on-demand (DOD) generator. For full details on this device, refer to Wood et al 31 The drops generated had an average diameter of 1.29 ± 0.06 mm (±2 SD). An Arduino Mega 2560 microcontroller prototyping board (Arduino Company) was used to activate the DOD device and the pneumatic sample accelerator in synchronization with the high-speed camera.…”