The formation of a simple coffee stain has been the subject of complex study for decades, though it turns out that there remain some stones still to be turned. Researchers in the College of Engineering have modeled how a colloidal w88 online casino betting evaporates and found a previously overlooked mechanism that more accurately determines the dynamics of particle deposition in evaporating sessile droplets, which has ramifications in many fields of today's technological world.
"Understanding and manipulating the dynamics of particle deposition during evaporation of colloidal drops can be used in DNA sequencing, painting, ink jet printing and fabricating ordered micro/nano-structures," Hassan w88 online casino betting, assistant professor in the Department of Mechanical w88 online casino betting, said. "And now we understand it better than ever before. Our discovery builds on a large body of work; we took an extra step though, modeling the interaction of suspended particles with the free surface w88 online casino betting drop. We believe our findings are going to fundamentally change the common perception on the mechanism responsible for the so-called 'coffee-ring' phenomenon."
When a droplet dries on a surface, the particles suspended in it usually deposit in a ring-like pattern, leaving a stain or residue, called the coffee-ring effect. Until now, the stain was thought to form as a result of the fluid flow inside the drop. w88 online casino betting and his team found that the free surface of the droplet, the top layer where it is in contact with the air, plays a critical role in the deposition of the particles.
"When the drop evaporates, the free surface collapses and traps the suspended particles," w88 online casino betting said. "Our theory shows that eventually all the particles are captured by the free surface and stay there for the rest of their trip towards the edge of the drop."
w88 online casino betting and his team used a less familiar modeling system, known as the Toroidal Coordinate System, that allowed them to reduce the three-dimensional governing equations into a one-dimensional form. Despite a decent amount of server space and speed, the team opted to write out their many equations long-hand, on dozens of very large pieces of news print paper.
"Our innovative approach - and using some ugly-long equations - distinguishes our work from previous research," he said. "No one else has used this coordinate system for this problem, and this allows us to track the motion of particles w88 online casino betting drop in a natural way."
w88 online casino betting evaporation manipulated
The discovery allows scientists to manipulate the motion of solute particles by altering the surface tension w88 online casino betting liquid-gas interface rather than controlling the bulk flow inside the drop.
"We can use surfactants to tweak the surface tension," w88 online casino betting said. "In a simple example, if you are cleaning solar panels, which can lose up to 90 percent of their efficiency when dirty, the preferred method of cleaning is water, but that leaves behind a stain that is hard to wipe out. Changing the flow dynamics during evaporation with a specialized cleaning agent can leave the panels cleaner and more efficient."
Their peer-reviewed paper, "Alternative mechanism for coffee-ring deposition based on active role of free surface," was published Dec. 12 w88 online casino betting American Physical Society's publication Physical Review E.
"Hassan's work is extremely creative and w88 online casino betting insights and method are very interesting," Miles Greiner, chair of the Mechanical Engineering Department, said. "He is an example of one of the many young and innovative researchers and educators in the department. I'm so pleased that w88 online casino betting work is appearing in 'Physical Review E,' which is a very selective and prestigious journal."
Masoud's team includes w88 online casino betting Saeed Jafari Kang, post-doctoral fellow Vahid Vandadi, and collaborator James D. Felske, who is a professor in the Department of Mechanical and Aerospace Engineering at the w88 online casino betting at Buffalo.
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w88 online casino betting leads the Complex Fluids and Active Matter Group at the w88 online casino betting. Before coming to the w88 online casino betting of Nevada, Reno's College of w88 online casino betting, he was a lecturer and post-doctoral fellow at Princeton w88 online casino betting. He received his doctorate from the Georgia Institute of Technology in 2012. His interests include fluid mechanics, transport phenomena and hydrodynamics of soft and active matter. He uses the tools of applied mathematics and high-performance computing to solve state-of-the-art problems at the intersection of engineering, physics and biology.
