At the droplet of a hat: Capturing mixable liquid interaction

June 28, 2016

When raindrops fall into bodies of water, milk is added to a cup of coffee, and in other mixing and rinsing processes, you might wonder how one liquid is absorbed by the other. Small droplets can be absorbed so fast that our minds perceive it to be instantaneous. However, in reality, there is much more to the process than first meets the eye.

In collaboration with Daniel Walls and Prof. Gerald Fuller from Stanford University, Dr. Simon Haward and Prof. Amy Shen from the Okinawa Institute of Science and Technology Graduate University (OIST) were able to, for the first time, capture the spreading of a droplet as it was immersed in a second mixable, or miscible, liquid. The results could have a far-reaching impact into general mixing, dilution, rinsing and washing processes, including how oil from oil spills mix with animal body oil. The paper describing these results has recently been published in Physical Review Fluids.

"There is always a clear interface between liquids that don't mix, say oil and water. For example, in salad dressing you can clearly see the droplets," Shen, co-author and head of OIST's Micro/Bio/Nanofluidics Unit said. "But when you have two miscible liquids, like water and vinegar, they will integrate with each other rapidly and that process is pretty difficult to study because the interface is much less clear."

In order to observe the interactions of multiple different pairs of miscible liquids, the team created a device that allowed a droplet on a glass slide to be slowly submerged into another liquid held below in a transparent cube. High speed cameras were set up around the device to document the way the drop spreads and then integrates into the second liquid. From the images, the team could see that the droplets spread in a way that made them look like little hats, with the brim continuing to spread over time until the droplet was fully integrated into the second liquid.

To further explore what happens in the liquid to create these droplet hats, the team added particles to the liquid and illuminated the particles with a laser. In this way, they could understand more about what was happening inside the fluid and why the droplet begins to look like a hat.

"We could see the motion of the fluid inside the droplets as the droplets spread out on the surface," Haward, co-author and group leader of OIST's Micro/Bio/Nanofluidics Unit said. "This made it very clear that the flow slides down around the top edges and the sides of the droplet, while the fluid in the center does not move."

"There is a qualitative difference in how the shape of liquid evolves when you have two miscible liquids instead of two immiscible liquids," Walls, Ph.D. student at Stanford University said. "And this is the first time that the spreading of miscible liquids has been captured in this way."

Haward added, "There are numerous potential applications. Understanding the spread of miscible liquids can be useful in many different fields."

Okinawa Institute of Science and Technology (OIST) Graduate University

Related Water Articles from Brightsurf:

Transport of water to mars' upper atmosphere dominates planet's water loss to space
Instead of its scarce atmospheric water being confined in Mars' lower atmosphere, a new study finds evidence that water on Mars is directly transported to the upper atmosphere, where it is converted to atomic hydrogen that escapes to space.

Water striders learn from experience how to jump up safely from water surface
Water striders jump upwards from the water surface without breaking it.

'Pregnancy test for water' delivers fast, easy results on water quality
A new platform technology can assess water safety and quality with just a single drop and a few minutes.

Something in the water
Between 2015 and 2016, Brazil suffered from an epidemic outbreak of the Zika virus, whose infections occurred throughout the country states.

Researchers create new tools to monitor water quality, measure water insecurity
A wife-husband team will present both high-tech and low-tech solutions for improving water security at this year's American Association for the Advancement of Science (AAAS) annual meeting in Seattle on Sunday, Feb.

The shape of water: What water molecules look like on the surface of materials
Water is a familiar substance that is present virtually everywhere.

Water, water everywhere -- and it's weirder than you think
Researchers at The University of Tokyo show that liquid water has 2 distinct molecular arrangements: tetrahedral and non-tetrahedral.

What's in your water?
Mixing drinking water with chlorine, the United States' most common method of disinfecting drinking water, creates previously unidentified toxic byproducts, says Carsten Prasse from Johns Hopkins University and his collaborators from the University of California, Berkeley and Switzerland.

How we transport water in our bodies inspires new water filtration method
A multidisciplinary group of engineers and scientists has discovered a new method for water filtration that could have implications for a variety of technologies, such as desalination plants, breathable and protective fabrics, and carbon capture in gas separations.

Source water key to bacterial water safety in remote Northern Australia
In the wet-dry topics of Australia, drinking water in remote communities is often sourced from groundwater bores.

Read More: Water News and Water Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to