Tuesday, 30 April 2013

Position Based Fluids Demonstration

Water is very difficult to simulate due to its surface tension and other dynamic properties.  Even for molecular dynamic simulations the air water interface is not so precise.  The video game industry is at the forefront of science and has helped drive computing to the cutting edge.  (Alan Turing would be proud!).  Games are approaching photorealism to the point that the movie the Matrix may be our new reality.  Water physics has been notoriously difficult to implement properly.   So what did people do?  They made a new algorithm.  
'A new fluid simulation algorithm (FSA) from PhysX appears to have made a breakthrough with its Position Based Fluids (PBF) technique that is based on the same Position Based Dynamics (PBD) framework used for simulating cloth and deformables in the PhysX SDK.
According to PhysX Info, PBD uses an "iterative solver" that allows it to "maintain incompressibility more efficiently than traditional SPH fluid solvers. It also has an artificial pressure term which improves particle distribution and creates nice surface tension-like effects (note the filaments in the splashes). Finally, vorticity confinement is used to allow the user to inject energy back to the fluid."
Further information on the technology is available in the following SIGGRAPH 2013 paperby Miles Macklin and Matthias Mueller-Fischer. The demonstration video (running on a single GTX 580) is available below.' via Toms Hardware.

Sounds legit.  Sound awesome.  Sounds like we are going into the Matrix.  

Thursday, 25 April 2013

Pulmonary Surfactant Life Imitates Art

Although a fluorescent monolayer experiment can look like a print from Merrimekko it is actually a film showing lipids, pulmonary surfactant and nanoparticles at an interface.  

What are pulmonary surfactants?

Pulmonary surfactants are needed in our lungs to aid in breathing.  The latter is a surface-active lipoprotein complex that binds to the former to do a number of things in the lung:

  • To increase pulmonary compliance or the ability for the lungs to inflate changing the volume.  The lung has a normal surface tension of 25 mN/m but at the end of expiration the pulmonary surfactant needs to decrease to near zero.  The lung surfactant takes the work away from breathing and allowing the lung to inflate easier.  This also helps to prevent the collapsing of the lung (with just lipids they might collapse on itself).
  • Aveolar size regulation.  If the pulmonary surfactants are more concentrated on small alveoli it helps to keep a constant rate of both alveoli and lung expansion.  When the alveoli are increased in size the pulmonary surfactants are spread increasing the surface tension (e.g. water is more bonded and less surfactant to separate it) slowing the expansion of the alveoli.
  • Keeping airways dry.
  • Pulmonary surfactant gives us innate immunity.  With our lungs one of the main entry points to the body (and many people get bronchitis at least once in their life) it is important to have something to prevent infection.

What are they studying in the above picture?

Since the lungs are a main entry point to the body and drugs can be fast adsorbed (as any smoker might know) scientists are developing new ways to study the lung.  To study lung surfactants you need a Langmuir Blodgett film where you can add the lipids (mostly DPPC) and the pulmonary surfactant (like SPC).  By using something like the Kibron Microtrough scientists can add carbon nanoparticles to see how they influence the the pulmonary surfactant.  As the above picture shows a snapshot of this is captured and different patterns are observed as a simulations is made by compressing the lipid layer from a gas phase (lung expansion/inhalation) to a more solid phase (lung contraction/exhalation).  

Tuesday, 9 April 2013

Relationship between Margaret Thatcher and Surface Tension

Margaret Thatcher was chemist who graduated from Oxford before she became a lawyer and a politician.  During her Chemistry endeavors she was known to have invented Mr. Whippy soft scoop ice cream at J. Lyons and Co.

Ice cream and milk in general has interesting surface tension properties.  In general ice cream is a colloidal dispersion.  Colloidal dispersion consists of small particles of one phase (solid, liquid or gas) in another continuous phase.  The particle size may range from an order of nanometers to microns.  The surface properties of the different phases can influence the properties as a whole.  A typical ice cream is 30% ice, 50% air, 5% fat and 15 % matrix (a sugar solution) by volume.  In this colloid suspension it is an emulsion, ice crystals and foam.

The interfaces between the two immiscible liquids in ice cream create in interfacial tension which is dependant on the surface area of the droplets.  One interesting thing that early ice cream manufacturers did was shake the ice cream.  This added air and the emulsion at the top was suspended in a foam.  Margaret Thatcher, the Iron Lady, used her chemistry skills add more air to this emulsion.  This created a lighter fluffier ice cream that cost less because air costs nothing.

Saturday, 6 April 2013

Surface Science in my refrigerator...soon

As a taxpayer you may think that you are wasting money on research at publicly funded Universities that you may never see in your lifetime, occasionally you are correct.  However, sometimes the research can go from lab testing to your home (or more specifically your kitchen) very quickly.

If you live in the Western world likely you have eaten ketchup.  Americans consume around 36 million tons of ketchup annually (ca 2008 chachacha).  The inventors of ketchup probably did not care too much about its fluidic properties.  The problem with ketchup is that it is a thixotropic fluid.  This means that under normal conditions it has a thick or viscous property but when the ketchup bottle is shaken or stressed it has a shear thinning property.  Many thixotropic fluids take a finite time to obtain equilibrium viscosity.  With ketchup the gel viscous state returns almost instantly.  Ketchup has another characterization calls a pseudoplastic fluid.  This is likely why designing a new kind of bottle was innovative.  

Originally, ketchup was in glass bottles and for anybody that grew up in that era it was always an interesting (and possibly slightly messy affair) to get the ketchup out.  With the advent of plastic ketchup bottles it allowed ketchup to be squeezed out.  Following this ketchup manufacturers  created bottles that can be set with the lid facing downwards so the ketchup settles at the top of the bottle.  With these bottles there is always some ketchup left these kinds of bottles and the bottles do not look so nice.

A designer and a scientist made a bottle and immediately found a purpose for ketchup.  The researchers at MIT introduced the LiquidGlide Ketchup bottle.  It has a coating that is composed of a porous solid layer that bonds to the surface of the bottle.  Another layer impregnated in this provides lubrication.  Varying the structure or materials used in the coatings, it can be tailor-made to any purpose and any level of lubrication be it for ketchup or other non-newtonian fluids.  The most interesting thing about this bottle is that some of the outer materials are edible.  In case you have a friend that wants to scratch off the surface and eat it.

'Sometimes the best inventions address persistent problems that people have kind of just given up on.'  That is why these researchers were a nominee for 2013 Design of the Year award and that they are on display at the Design Museum in London.  Yes, all for understanding some physicochemical properties ketchup and making a hydrophobic bottle.  Surface tension and viscosity have no clear correlation and in the case of ketchup flowing surface tension should be negligible.  However, in the glass bottle since it is superhydrophobic the surface tension effects on the surface of the ketchup are important in order for the MIT designed ketchup bottle to work.