Self-propelling coalescing droplets

submitted by: msellier
Microfluidic devices play an ever increasing role in nano- and biotechnologies. An emerging area of research in this technology-driven field is digital microfluidics which is based upon the micromanipulation of discrete droplets. Microfluidic processing is performed on unit-sized packets of fluid which are transported, stored, mixed, reacted, or analyzed in a discrete manner. An obvious challenge however is how to displace sessile droplets on a substrate. The video presented here illustrates...

Drying of poly(ethylene oxide) droplet viewed from beneath

submitted by: David Fairhurst
Drying of a 75μL droplet of 20% poly(ethylene oxide) solution in water, viewed from beneath using an inverted microscope (Nikon Eclipse TE2000-S) with 2x objective lens. The image measure 5mm across and the frame rate is increased by a factor of 300. The bright specks in the droplet are small clusters of polymer that would not dissolve, and help to visualise the flow within the droplet. Pinned drying (stage 1) occurs for the first 5 seconds, during which there is clear evidence for...

Drying of 40% poly(ethylene oxide) droplet

submitted by: David Fairhurst
Drying of a 75μL droplet of 40% poly(ethylene oxide) solution in water. The duration of the experiment was approximately 2 hours, the distance across the image approximately 10mm. Timings given below are given relative to the video, to aid identification of the various stages and processes. The droplet shows a very short stage 1, around 1 second. The contact angle increases until 3 seconds and bootstrap deposition (stage 3) continues until 4 seconds. However, there is still liquid inside...

Drying of 25% poly(ethylene oxide) droplet

submitted by: David Fairhurst
Drying of a 75μL droplet of 25% poly(ethylene oxide) solution in water. The duration of the experiment was approximately 2 hours, the distance across the image approximately 10mm. Timings given below are given relative to the video, to aid identification of the various stages and processes. The droplet exhibits stage 1 pinned drying for the first 5 seconds. However, the solid deposit is already much thicker for this droplet, than those with lower concentration. As the contact angle is...

Drying of 8% poly(ethylene oxide) droplet

submitted by: David Fairhurst
Drying of a 75μL droplet of 8% poly(ethylene oxide) solution in water. The duration of the experiment was approximately 2 hours, the distance across the image approximately 10mm. Timings given below are given relative to the video, to aid identification of the various stages and processes. The droplet exhibits pinned drying (stage 1) for around the first 5 seconds, at which point the contact line depins and the droplet undergoes a dewetting transition (stage 2) until 9 seconds. At this...

Drying of 5% poly(ethylene oxide) droplet

submitted by: David Fairhurst
Drying of a 75μL droplet of 5% poly(ethylene oxide) solution in water. The duration of the experiment was approximately 2 hours, the distance across the image approximately 10mm. Timings given below are given relative to the video, to aid identification of the various stages and processes. The droplet exhibits pinned drying (stage 1) for around the first 5 seconds, before depinning when the contact angle becomes lower than the measured receding contact angle. Stage 2 and bootstrap...

Liquid Mirror Droplet

submitted by: andrewsun

Tiny mirror platelets with amphiphilic sides assembled into a mirror at the oil-water interface, rendering the oil droplet a liquid mirror. This is the supporting info of a Langmuir paper, DOI: 10.1021/la803537v.