surfactant

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Couple weeks ago, Tumblr introduced me to a natural, cheap, almost odorless, hypoallergenic, and sustainable cleaning agent called soapnuts (or soapberries)! The dried husk/shell of this fruit contains resin that is high in saponins, a naturally occurring chemical compound that reduces the surface tension of water so that it can penetrate and dislodge the solid/other liquid more effectively. Extraction of the active ingredient only requires that soap nuts be agitated in warm water; a lot of lathery foam will form. I’ve tested soap nuts as a

  • laundry detergent
  • body and hair cleanser
  • fruit/veggie and dishwashing cleanser
  • insecticide for my indoor plants

So far so good, although not fond of using it as a body cleanser; it’s too awkward to apply IMO. There are plenty of other uses, but I think this would be a particularly excellent ecofriendly way to bring along a camping trip to clean your wares.

To my gardeners: Trust me, I checked every pod. No leftover seeds, otherwise I would definitely plant a soap nut tree!

SURFACE TENSION DRIVEN FLOW
Droplets of oleic acid spread across the surface of a silicon wafer
coated with a thin liquid film of glycerol

Princeton Art of Science ]
Image by Anton Darhuber, Benjamin Fischer, and Sandra Troian
Princeton University.

The usually slow spreading process was accelerated by the surface tension imbalance, which triggered a cascade of hydrodynamic instabilities.

Such surface-tension driven flow phenomena are thought to be involved in the self-cleaning mechanism of the lung as well as pulmonary drug delivery.

[Thanks to biocanvas for the April 2012 post of this image.]

Clean-up of accidents like the 2010 Deepwater Horizon oil spill can be complicated by what goes on beneath the ocean surface. Variations in temperature and salinity in seawater create stratification, stacked layers of water with differing densities. When less dense layers are on top, the fluid is said to be stably stratified. Since oil is less dense than water, one might assume that buoyancy should make an oil plume should rise straight to the ocean surface. But the presence of additives or surfactants in the oil mixture plume can prevent that. With surfactants present, an oil mixture tends to emulsify, breaking into tiny droplets like a well-mixed salad dressing. Even if the density of the emulsion is smaller than the surrounding fluids, such a plume can get trapped at a density boundary, as seen in the photo above. Researchers report a critical escape height, which depending on the plume’s characteristics and stratification boundary, determines whether a plume escapes or becomes trapped.  (Image credit: R. Camassa et al.)

Altering the shape of water drops.  Water drops are spherical due to surface tension , that is, because of cohesive forces. Water molecules want to be adjacent to one other and far away from molecules that are different from them, like air or oil molecules. This has the effect of minimizing water’s surface area; hence, water drops are spherical. This is shown in the upper image of spherical water drops flowing inside a jet of oil. To reduce cohesive forces or surface tension, actually the interfacial tension between water and oil, surfactants, such as soap, are added to water. Since surfactant molecules have two ends, one that is attracted to water and one that isn’t, surfactant molecules disrupt the cohesive forces at the interface.  Consequently, if the surfactant molecules are strong enough and the disruption of the cohesive forces is widespread, the spherical shape of water drops no longer prevails. This is shown in the bottom image.  (Photo credit: L. L. A. Adams)

August 7, 1963: Trying to Save the President's Baby

Sometimes, it’s easy to forget how far we have come in the past fifty years. On August 7, 1963, First Lady Jackie Kennedy delivered her second son, Patrick Bouvier Kennedy. The baby was five and a half weeks premature and weighed 4 pounds 10 1/2 ounces. Today, a baby born at 34 weeks enjoys a 98% survival rate. However, in 1963, if the premature baby developed respiratory distress, odds were that the baby would die. There simply was no treatment at that time. Sadly, in the early morning hours of August 9, 1963, as President Kennedy stood watch, Patrick Kennedy succumbed to “hyaline membrane disease”, despite being cared for by the most knowledgable medical team in the country.

Interestingly, when Patrick Kennedy died, most doctors didn’t even really understand what caused “hyaline membrane disease”. The common theory was that a glassy membrane formed making it nearly impossible for the baby’s lungs to extract sufficient oxygen when air was inhaled. However, after decades of research, doctors finally realized that 

(h)yaline membrane disease was not caused by the presence of something in the lungs but rather by the absence of something. The lungs of babies who died of hyaline membrane disease lacked a substance called surfactant, which lines the alveoli, the small air sacs at the end of the lungs’ numerous, branching airways. The problem did not lie only with breathing in, as had long been assumed, but also with breathing out. The baby took that first breath, perhaps even a good deep breath, as any baby would. But if the newborn baby’s immature lungs lacked surfactant, the alveoli tended to collapse when the baby breathed out. 

This understanding led to the eventual development of artificial surfactants, the practice of giving steroids (which speed up the natural production of surfactant) to women at risk of premature labor, and the introduction of better ventilator/respirator technology & methods. 

When people ask me if I want to return to a simpler time such as the 1950s or early 60s, I always think (for many reasons), “Are you crazy?” I have no desire to return to a time where infants born at 34 weeks had a 3% survival rate. Today that survival figure is 98%. Think about that. It’s a truly remarkable turnaround in a relatively short number of years. On what would have been his 49th birthday, I pause to pay respects to baby Patrick whose short life undoubtedly attracted public attention to hyaline membrane disease and helped fuel further research, leading to effective treatments that save the lives of tens of thousands of newborns each year. 

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It is common in many industries to use oil as a defoamer to break up existing foams or prevent foams from forming. But with the right surfactants—additives that change the foam’s surface tension—it’s possible to make aqueous foams that are actually stabilized by the presence of oil. This video explores some of the ways that oil can interact with these kinds of foam, beginning with capillary action, which draws the oil up into the junctions between foam films. For more, see Piroird and Lorenceau. (Video credit and submission: K. Piroird)

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What an eclipse would look like from the surfact of the moon

Science art: Driven. Evolving patterns over film on silicon wafer
Anton Darhuber, Benjamin Fischer and Sandra Troian
Microfluidic Research and Engineering Laboratory, Department of Chemical Engineering

This image illustrates evolving dynamical patterns formed during the spreading of a surface-active substance (surfactant) over a thin liquid film on a silicon wafer. After spin-coating of glycerol, small droplets of oleic acid were deposited. The usually slow spreading process was highly accelerated by the surface tension imbalance that triggered a cascade of hydrodynamic instabilities. Such surface-tension driven flow phenomena are believed to be important for the self-cleaning mechanism of the lung as well as pulmonary drug delivery.

source: Art of Science Competition

Differences in surface tension cause fluid motion through the Marangoni effect. Because an area with higher surface tension pulls more strongly on nearby liquid than an area of low surface tension, fluid will flow toward areas of higher surface tension. Here surfactants, shown in white, are constantly injected onto a layer of water dyed blue. You can also see the flow in motion in this video. Outside of the central source flow, the pattern features lots of 2D mushroom-like shapes reminiscent of Rayleigh-Taylor instabilities. But these shapes are driven by variations in surface tension rather than unstable density variations. For more, check out the original paper or learn about other examples of Marangoni effect. (Photo credit: M. Roché et al.)

Viscoelastic fluids are a type of non-Newtonian fluid in which the stress-strain relationship is time-dependent. They are often capable of generating normal stresses within the fluid that resist deformation, and this can lead to interesting behaviors like the bead-on-a-string instability shown above. In this phenomenon, a uniform filament of fluid develops into a series of large drops connected by thin filaments. Most fluids would simply break into droplets, but the normal stresses generated by the viscoelastic fluid prevent break-up. For this particular photo, the stresses are generated by clumps of surfactant molecules within the wormlike micellar fluid. Similar effects are observed in polymer-laced fluids. (Photo credit: M. Sostarecz and A. Belmonte)

Another cool thing I’ve learned since starting medical school: lamellar bodies. Produced by Type II pneumocytes deep in the lung, they contain the protein and phospholipid components of surfactant. Surfactant decreases surface tension in the small alveoli to keep them from collapsing. 

Also, pretty bad ass that this picture was taken by shooting electrons through/around shit that’s so tiny.