Drugs into the Blood Brain Barrier???

I saw this poster at the AAPS a couple of years ago that showed how certain drugs based on their physicochemical profiles can get into the blood brain barrier.  It was then made into a full paper by a group in Germany.  I just learned that the lead author Anna Petereit won the Awarded in 2010 for the best paper by the European Journal of Pharmaceutics and Biopharmaceutics. Prediction of blood-brain barrier penetration of poorly soluble drug candidates using surface activity profiling.  (A.C. Petereit, J.B. Dressman et. al  Eur J Pharm Biopharm. 2010 August;75(3):910-923).  It is really a nice piece of work.  In the materials and methods they used Kibron's Delta-8 instrument to do a lot of the profiling. 

I will talk about the blood brain barrier later..... (I should read the paper again).

Water vs. Oil

I read this magazine called Cosmetics and Toiletries Magazine.  Mr. Tony O'Lenick writes this column called compartiatively speaking.  I am a fan of his column and understanding cosmetics in general.  You probably use some sort of cosmetic or toiletry product everyday to wash your hair with a detergent, wash your hands with a soap or apply some makeup to your cheeks.


Did you ever think what all that stuff is in that package?  Some it is preservatives, colorants, maybe some non-medical cosmetic ingredients (aloe vera) and lastly surfactants.  What is a surfactant though?  It is a material that interacts with the surface of the water to break those hydrogen bonds and lower the surface tension of the water.   This is needed in cosmetics as lowering the surface tension of a solvent is a prerequisite for wetting, spreading, foaming and emulsification.   However, not all molecules that lower surface tension will provide all these functions, but to achieve these properties companies want to make a product that can lower the surface tension to achieve these desirable properties.

As mentioned before (and the name of this blog) water has a surface tension of 72 dynes/cm which is relatively high.  It can be lowered into the range of 32–35 dynes/cm with traditional water-soluble fatty surfactants (for some of the ingredients look at the back of your cream). Consequently, properly selected fatty surfactants can wet, foam, emulsify or facilitate spreading in aqueous solutions.

If you have ever put oil in water when washing dishes you notice that oil differs from water in many respects, the most important of which is surface tension. Oil has a surface tension of 30–35 dynes/cm, meaning that oil-soluble fatty surfactants do not provide the desired surface tension reduction for oils. However, as Mr. O'Lenick mentions several classes of compounds can provide surface tension reduction below 30–35 dynes/cm.  These are based upon silicone and its fluoro compounds.

These silicone surfactants can reduce the surface tension of oils to 20-25 dynes/cm.  Fluoro surfactants can reduce this below.  The ability of these surfactants which are amphilphilic molecules (molecules with a water liking head and a water disliking tail) to orient properly at the surface to reduce the surface tension of water and perhaps the oil that is in the water is what formulators want and what we want to put on our skin.  When you are in the bathroom take some time to look on the back of the package and see if there are fluorsurfactants, surfactants or other things in there that help the ingredients work nicely on your body.

12 Apostles vs. 1 Newton

 I was thinking about Jesus and his walk on water.  It is considered to be one of the miracles of Jesus in the Gospels.  I should just say that you can believe whatever you want, there is no right and wrong answer but I am merely providing a physical answer to a biblical miracle.  Accounts of this miracle appear in the Gospels of John (John 6:16–21), of Matthew and of Mark.  This is what it says: Jesus sent the disciples in a boat, ahead of him, to Bethsaida.  When they were half way across the Sea of Galilee, Jesus walked over the lake water and met them.  I like many have tried to walk on water like say a water strider.  Physically it does not work. So I started trying to understand the properties of water and other fluids further.  The surface tension (easy), the tensile and compressile strength and finally the viscoscity were understood. 

To reiterate from previous posts surface tension is the property of the liquid at the water air interface the tension here that resists force.  The tension here is due to different forces mainly hydrogen bonding as in the rest of the liquid.  Its properties change mostly from the temperature or from the addition of specific chemicals (like soap).  Both will decrease the surface tension by changing the bonding between the water molecules.

The tensile and compressive strength also relates to the bonding in the water.  The bonding here more relates to the bonding underneath the surface between other water molecules.  Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. 

Viscoscity relates to the shear rate whereby the liquids resistant can be deformed or moved.  This is caused by the friction between the molecules.  Viscocity properties however change depending on the type of fluid: Newtonian and Non-Newtonian.  (This is of course named after Isaac Newton who developed classical mechanical theories).  A Newtonian fluid react to forces in a linear manner.  However, non-Newtonian fluid, the relation between the shear stress and the shear rate is different, and can even be time-dependent. Therefore a constant coefficient of viscosity cannot be defined.  For example the polymer that you put on your French Fries, Ketchup, is stable at rest but becomes fluid when agitated.  Other Non-Newtonian fluids like clay (thixotropic - time dependent fluid viscosity decreases with increased stress) or cornstarch independent (dilatant - time independent viscoscity increases with increased stress).  Viscosity is thus about movement and the shear rate on a particular substance being newtonian or non-newtonian. 


To summarize, what property in water water would allow Jesus to walk over water?
Surface tension: The boat would be floating due to surface tension
Compressive strength: probably not since he would most likely sink under normal gravity
Viscoscity or shear: This would probably be the property of water that would allow someone to walk on it if water were a non-Newtonian fluid in particular a thixotropic non-Newtonian fluid.  One that becomes harder when you step on it. 

So we can subtly rewrite the story accounted in John with some classical mechanical physical principles added  (I wonder if anybody has written The Physics of the Bible?).  Jesus saw that his disciples in the boat were freaking out because of some storm or earthquake.  Jesus obviously wanted to help them but he did not have a boat.  An earthquake or volcanic eruption in the region could have caused the bedrock beneath the Galilee Sea to shift. Layers of sediment at the bottom of the lake began to rise, mixing with water and turning it into a gel-like thixotropic fluid.

At the time of chaos and panic, no one would pay much attention to the thixotropic properties of the water.  However, Jesus was pretty smart (and may have learned something about physics somewhere) and probably wanted to set an example for his followers (like Dr. Albert Hofmann did with LSD which fair enough will also allow you to walk on water) and waded out into the deeps only to discover that he could actually walk on water due to the thixotropic fluid supporting him.  The boat on the other hand would be still floating due to the surface tension of the water.  Yes science is magic and can even be considered a miracle.  I would imagine it would look something like this (except with a thixotropic clay and not a dilatant cornstarch like fluid).

A surface tension joke...

I am a total nerd so I made a joke.

Two male beers a Heineken and a Karhu are talking at a bar.  At the table the Karhu beer's wife, a Riesling (a multibeverage marriage) sits.  Heineken notices the Riesling crying and turns to her husband, 'Why is your wife crying?'  He replied:

'She gets all teary and volatile from the alcohol.'

Your Wine's Got No Legs

Tonight you may to go home after a long day of work. You might stop off at the Alko (in Finland) or another store to buy wine. You might select a nice bottle of Valpollicello or something off the shelf that you select to be good. A decent bottle that is not flabby, volatile, stale or diffuse should cost you at least 10 euros here in Helsinki (in other places in the world this might differ. You get home put your feet up, pull out a clean large wine glass.

If you are a wine enthusiast or just pretentious you might swirl the glass of wine, raise it towards the light and watch with bated breath for the wine's legs to appear. These legs are also referred to by the French as tears, curtains and perhaps church windows. If they appear you will say to yourself and think back on the price, 'What a great bottle of wine I selected, great job. I have to go watch the movie Sideways again to learn more wine terminology.' So I asked myself as a scientist, a wine enthusiast (who has been to his fair share of wine tastings, vineyards and whatnot). What are these legs? And how can you tell the wine's quality by the legs they have.

Wine is a inhomogeneous mixture of alcohol and water, the alcohol has a faster evaporation rate and a lower surface tension than water, effectively forcing the alcohol to evaporate at a faster rate. This dynamic allows the water's surface tension and concentration to increase, pushing the legs up the smooth surface of the glass until the surface tension pushes the water into beads. Finally, gravity wins the battle and forces the liquid to tear down the glass in a defeated streak. The surface tension gradient can be caused by concentration gradient or by a temperature gradient (surface tension is a function of temperature) so maybe if you chill the wine you might not see as many tears. So as I mentioned earlier someone actually has studied this and they were someone who probably drank a lot of wine (why just throw your experiment down the drain when you can put it down the hatch). He called it the Marangoni effect (also called the Gibbs-Marangoni effect) is the mass transfer along an interface between two fluids due to surface tension gradient. And in the case of temperature dependence, this phenomenon may be called thermo-capillary convection (or Bénard-Marangoni convection).

So the tears are a mythical indicator of wine quality. And now if you would be pretentious if you said, 'This indicates the wines quality.' However these legs tells quite a bit about the wine's power and the wine's body (and perhaps if you have a clean glass). If the wine has a lot of alcohol or a lot of sugar it will have longer tears at the right temperature. If you are still not convinced that it's physics and not quality that drives this phenomenon? Try covering your next glass of wine and see if the legs present dramatically decrease when covered compared to when open. No evaporation, no legs. Enjoy none the less.

Be water my friend....

I love Bruce Lee. I love him for many reasons. I love his films and the impact they have on other martial arts industry. I love that he was one of the first mixed martial arts fighters (MMA) learning and mixing styles something that I am aspiring to do (with Savate and grappling). Mostly though I love his philosophy. I love this his quote below on not using a specific fighting form but emptying your mind and 'becoming water' that was taken from his dialogue in the short lived TV series Longstreet.



'Don't get set into one form, adapt it and build your own, and let it grow, be like water. Empty your mind, be formless, shapeless — like water. Now you put water in a cup, it becomes the cup; You put water into a bottle it becomes the bottle; You put it in a teapot it becomes the teapot. Now water can flow or it can crash. Be water, my friend.'

However, I wish to extend this quote....with the idea of surface tension and the compressibility of water.

'If he hits you can absorb the force (of the punch with your entire body) like water. Hit back with the intense force of water. You fists can become as strong as the water below a bridge that a man crashes into when jumping. The water can be soft or it can be hard. Be water my friend.'

You can practice this with a bag made of water like the Title Liquishock. This bag is harder to train with because the water compresses and the force flows out of from the impact but still maintains tensile strength not to absorb all your punch.

Skin Critical Surface Tension

I was thinking today how can skin get more wet? (Actually I just wanted to post a video of someone getting hit by a water balloon). I am not sure yet. However, I found some answers on this thing called the internet. Someone managed to solve it. A. El Khyat et. al (2006) mentioned that the skin critical surface tension (CST), an index of wettability. As you can see from the video below the skin surface is primarily hydrophobic (so not all the water is absorbed to it although the balloon is moving quite fast in slow motion) and paradoxically becomes more wettable through its lipidic component.

Forehead CST was above 50.7 dyne/cm and by defatting (getting rid of some of the fat) it reduces the skin surface tension. However, by replacing some of the fat (naturally or with cream) your skin becomes more wettable.




Note: The CST was calculated using the Zisman equation, from the contact angle at equilibrium, of droplets of liquids whose surface tension was known. Contact angles were computed from the base and the height of the droplets viewed from their side through an operating microscope provided with a slanted mirror. Both volar forearm and forehead were studied.

Grande dark roast leave space for milk

You probably drink coffee everyday. If you are like me you might be a coffee addict which means two-three cups anytime. Right now I am drinking strong, not very tasty Presidentti Coffee in my office in Helsinki. The only thing that I take for breakfast are morning coffee and a cold walk to work.

Today I started to examine what is exactly in my cup. Since I am in science I started to deconstruct everything in my cup. I have water, milk, and dark coffee. Simple right? Well I looked deeper and found a little more than just that. You can always find more if you are willing.

The surface tension of water at room temperature is 72 dynes/cm. A dyne the measurement of surface tension described as the force required to accelerate a mass of one gram at a rate of one centimetre per second squared. So this unit describes the property of the surface of a liquid that allows it to resist an external force. Water can resist mass being put onto arising from surface tension. This is why it can stay in the cup and I can drink it as compared to (Acetone having a low surface tension and would evaporate and mercury having a high surface tension and probably difficult to drink). The fastest way to do this was with the Kibron (static) tensiometer we have in our lab. All measurements including the brewing of the coffee took me about 15 minutes.

Water changes its surface tension depending on its temperature so colder water means a higher surface tension and hotter a lower surface tension. We use a Moccamaster drip coffee machine which boils the water to 92°-96°C. The water had a surface tension of 58.4 dynes/cm.

The temperature of the water helps in the extraction process in brewed coffee. The lower temperature (below that of 88 C) will make weak coffee too high will make bitter or overextracted coffee. The surface tension, vapor pressure and polarity are perfect for extracting caffeine at that temperature (for reasons I won't explain here). Caffeine can also be extracted by organic compounds dichloromethane or benzene (volatile below 20 dynes/cm) to give you decaffeinated coffee.

Lastly there is the milk. Normally I do not put milk if the coffee is good but this stuff is just merely drinkable. A little milk will make it a little bit more bearable. The surface tension of milk depends on the fats in the milk. Homogenized milk which I used increases the surface tension of the milk. Milk has a lower surface tension than water though (44.9 dynes/cm) . If the milk was left out bacteria cultures might break down the fats into smaller free fatty acids lowering the surface tension even more. These free fatty acids give it a rancid flavor. Luckily, I did not put rancid milk in my coffee.

Since I used drip coffee made from MoccaMaster and not an expensive expresso machine I found this coffee quite flaccid with a surface tension of 46.5 dynes/cm and after adding some milk it lowered the surface tension to 43.3 dynes/cm.

I was wondering why just plain old drip coffee can be so boring while an expresso can delight your senses. So, I read from here that the 'lower surface tension enhances the ability of the liquid to coat the papilla where the taste buds are located, thereby enhancing your ability to sense flavor. The lower surface tension also enables the tiny oil droplets to penetrate the pores of the papilla and slowly release the aromatic substances that have bound to the oils. This accounts for the noticeable after taste of coffee brewed in an espresso machine.' However, it really depends on the wettability of the coffee which is measured using a slightly different device to see how the wettability changes over time on a surface. Espresso coffee beverage may be a effective wetting agent for the oral cavity than regular Presidentti coffee giving it a better taste as suggested by Padday (1978) and further corroborate by Ferrari et al.(2007).

I will forever be chasing that perfect cup of coffee. I might just have to go live in Italy where I only pay 0.80 cents for perfection.

(All images were awesomely taken by my colleague Kim)

Du-sty Du-sty Du Nuöy Ring

So I went to the lab today. I was just hanging around checked some emails. I as working on a paper when one of my colleagues stopped me. Since I was doing nothing at the time and I am a senior person in the lab I had no way of getting out of not helping with a problem. Even worse he wanted to use one of the tensiometers in our lab to measure the surface tension of his samples. Actually this was a tensiometer that was sitting in the back of the room on an expensive nonvibrating table. It had a fairly old computer but the whole system could not have been that old. It was an old Du Nuöy ring method with a platinum Du Nuöy ring encased in a cylindrical glass and plastic case. A thin layer of dust was on the top of the device.

I looked at this thing. This was the first time I saw it. This device was like that ugly lamp in the room that you inherited from your Aunt Hilda but nobody really turns it on or wants to use it. This device was not even plugged into the wall. My colleague and I set it up even managing to get rid of the dust off the device. We cleaned out the cup which had something dried on it. We then proceeded to turn on the computer. A log file opened and communicated with this Du Nuöy ring Tensiometer.

'So what do you want to measure?' He told me he had extracted and purified these oxidized phospholipids from cells that with lipid peroxidation. It had taken him a week to do the experiment. He wanted to measure the property of them using this Du Nuöy tensiometer. We filled the cup with 10 ml of water. We wanted to calibrate the thing. When we calibrated it was reading a value completely off from the value of the buffer of 72.8 dynes/cm.

So I took the ring out and looked at it. 'Just as I expected it is bent.' I called another colleague over who was senior to me and took out this kit for rebending the ring. Yeah the instrument has a freakin' kit that you need to rebend this fragile platinum ring. 'Why don't we just order a new one?' 'They are 800 euros my colleague replied.' After 40 minutes we managed to get a decent value for water.

My colleague then started to put his valuable lipids to try to get Critical Micelle Concentration ((CMC)the concentration where they are start to form micelles). The most accurate way is by measuring the surface tension. You can also measure the dynamic light scattering but we prefer this method in our lab. So he spreads in increments his precious lipids onto the water. And we start to measure. Add some more, measure. We have to waste a lot on this method because of the volume and it was taking forever. To get the CMC value with the ring you have waste a lot of lipids and you have to do it a number of times.

My boss was in the back of the room watching what we are doing. Sometimes he just watches to see if we are doing things correctly. It is science and sometimes you can do things by trial and error. However, he does want us to get our work done nicely and accurately. He kind of smiled like a father smiles when his son does not have the experience to do something the easy way but just likes to see them struggle at it to see if you can figure it out. Like the time I was struggling moving a huge couch when my father said it had wheels underneath. Often I do not figure it out.

So my boss came over. 'What are you doing?', he said in a slight Finnish accent. The explanation was fairly obvious but we explained it to him. 'Why don't you use the Delta-8?' The Delta-8 was an eight probed tensiometer that works with a slightly different technology, the Padday method. The Delta-8 sat on the opposite side of the room. It was sleek, easy to use and it was constantly being used someone in the lab. Neither me or my colleague had experience using it though. My colleague decided to use one that he heard about in some old journals from the 1970s. My boss showed us in about 10 minutes how to use it. The Delta-8 works with 96 well plates so you can vary the concentrations and you do not need to use that much lipids. Best of all it is self cleaning! We reproduced results 12 minutes after to find the CMC was 23 mM. A result that will go in the paper. I hate wasting time but sometimes science is time well wasted.

The Art of Surface Tension Science

Recently I heard about a sculptor in China that does sculptures on water. His name is Danny Lee Chin Fai, and he has given a sense of weight to the “water” (which is polished metal)– I can feel the surface tension holding the drop in its shape and the gravitational pull moving it onto the floor. It reminds me of Dali's melting clocks but you can appreciate more of the natural physical aspect of his sculptures because you can see it everyday when you pour a glass of water.

The sculpture has a caption on his work in the Hong Kong airport that reads: “Nature is all around us. Yet often we look but do not see. Next time you see morning dew, take a look at just one small dew drop. See your surroundings reflected there. Look closely and you will see a reflection of yourself. So why not pause and try to look at ourselves, objects and people around us from a fresh perspective?”

As a scientist I have to be creative to solve problems, and to make theories about biology based on research recorded at micoscale measurments. I feel like an artist of sorts. It is sometimes crazy how art and science mix. And it is amazing how you can get a great perspective from understanding one or the other. In many cases in both professions people are skeptical and are uncertain about their own work. Also oppressive sociopolitical factors affect both art and science a lot.

Also it is funny as a scientist to view art and probably as an artist to view science. To mix those two makes a phenomenal picture like Danny Lee Chin Fai did. Science always as to art and everything else. Richard Feynman has a quote on this, 'I have a friend who's an artist, and he sometimes takes a view which I don't agree with. He'll hold up a flower and say, "Look how beautiful it is," and I'll agree. But then he'll say, "I, as an artist, can see how beautiful a flower is. But you, as a scientist, take it all apart and it becomes dull." I think he's kind of nutty. [...] There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower. It only adds. I don't understand how it subtracts.' By understanding surface tension, the cohesive forces of water, and how you could break those cohesive forces one can understand and add to science and most likely art.

More Water in Space

Airbending Space.... pretty cool.

The Last Airbender

My friend wanted to me to see the last Airbender. M Knight Shamalan's movie based on the comic book/cartoon of the same name. It is fantasy and I'm not that much into fantasy or M. Knights movies too much. I am a little glad that I did not fork the eight euros for a ticket because I heard it was not so great. I think it won a number of Razzies for worst film, worst director, and worst special effects. In the clip the last Airbender bending water though. Shouldn't it be also called the last Thingbender. Maybe that doesn't not have such an appealing name. But bending water that is really cool (not cool enough to see the movie but cool). Water bending is a technique in the martial arts Shaolin and Tai Chi.

So I looked on my shelf and saw the book the Physics of Superheros. Great book made by a Professor James Kakalios of Physics at the University of Minnesota. Kakalios does not set out to show where the world of superheroes contradicts modern science, granting the heroes one or more "miracle exceptions" from natural law. Instead, he focuses on examples of comic book scenes that can be used to understand the diverse laws of physics from an unusual angle,It talks if the superpower were possible e.g. if the superhero could have this power what are physics behind making it happen if the physics in our world do not change. I tried to apply the same methodology to the last Airbender bending water. The last Airbender's power is the ability to manipulate water. This is possible if you take a comb This means that he must have some kind of electrical charge or to be able to pick up balls of water on earth. From this space video you can see that the in space with no gravity the surface tension is not trapped by the configns of gravity and in this case surface tension wins. However, the last Airbender is supposedly on earth so this kind does not apply. I would also not assume that somehow he makes a microgravity around the water. The water's cohesive forces should allow it to stick together though. However you can bend water by placing it in a charged field. The molecules that make up the water (H2O - hydrogen and oxygen) form a bond that is polarized - which means that it has a slightly positive end and a slightly negative end and are neutral. This means that when you put water molecules in a charged (magnetic) field, you can bend it by having a negative charge. To understand the effect electrostatic interaction between electrically charged particles in a electric field (Coulombs Law) you have to understand classical electromagnetism.

I mentioned above that in the absence of a gravitational field you might you can see the water particles sticking together. Interestingly enough Coulomb's law (interaction of electric charges and Newton's law of universal gravitation have parallels e.g. both are central and conservative, obey inverse square law of r, propagate at speed of light, electric charge and relativistic mass are conserved.

They have some differences e.g. electrostatic forces are much greater 10xE36 more than gravitational, gravitation attracted to like charges, electrostatic forces repulsive for like charges, gravitational forces are always attractive whereas electrostatic forces can be positive or negative. So the last air bender would have to be made a lot of charged particles (not sure how much) in order to bend water and throw it at his enemies... (calculations later)

Coulombs Law

Newton's Law

Newtons Law

Go ahead tough guy bend some water. Or you know if there are like bullies around just tell them you can bend water like a Shaolin monk. Then pull out your comb go to the bathroom and turn on the tap. I guarantee it here that you will not get the crap kicked out of you. Figure it out here: http://www.smarterthanthat.com

Putting Acetone into Milk.

What happens when acetone is added to green dyed milk? Surface tension pulls and spreads dyed milk after acetone is dropped on the milk surface, illustrating the Marangoni effect.

The Marangoni effect (also called the Gibbs-Marangoni effect) is the mass transfer along an interface between two fluids due to the surface tension gradient. This phenomenon was first identified in the so called "tears of wine" and was studied by the physicist for his doctoral dissertation (of course he is Italian why not study wine). It can also be done if you spread some water on a smooth surface and then add some alcohol (like vodka) to the center. You will see that the liquid will rush out of the region where the drop fell. This is similarly shown to the picture above with milk and acetone.

STRIDEs (Surface Tension Robotic Insect Dynamic Explorer)

Growing up we used to go to the lake and see these bugs, called water striders on the water.  They were really cool and it was always fascinating to watch them skip on the water.  I tried doing that.  It didn't work.  But the water striders were also fascinating to someone else.  He made a robot of emulated to these water striders which allows them to skim on the surface of the water seamlessly (unlike me). Click below for the full story.

Robot walks on water

Water striders, insects that walk on the surface of the water, may never set foot on land in their lives, and yet they’re not swimmers. Over the past million or so years, this insect—sometimes called a water skater—has optimized its use of surface tension to balance its 0.01-gram body on lakes, ponds, and even oceans.

Surface Tension in Space

I think any kinds of experiments that you look into the natural world of things is awesome.  When I go to work everyday and try to understand something about biochemistry I am amazed about how fun it is.  I guess that is why I became a scientist.  Asking a question is explosive.  Asking the right ones can change the world.  When you ask a question in the natural sciences you think about the parameters heat, motion, ionic strength, interacting chemicals ect.  What about gravity?  In order to do that you need to go to space (the final frontier)....

Don Pettit is the Science Officer on the International Space Station.  He asked, 'What happens to thin films and bubbles might in zero-g."  Everybody has made a thin film of water, soap and glycerin.  If you have not go do it right now.....Ok take a loop of thin wire 3.5 cm - 15 cm and blow through it you will get a bubble.  Pettit first tried it with just water. On earth a small thin film can be made with a 1 cm diameter wire which is very fragile.  His however was 4 cm and very easily he can  move it in the room and put food coloring on it.

So then you ask, 'What is happening?'  The electrical attraction between water molecules, and thus the surface tension of water, is the same on Earth and in space. There's no difference.  What is different is the competition between surface tension and gravity.  Surface tension therefore wins the competition with gravity, and the result is a sturdy long-lasting membrane. "Some of our films lasted longer than 12 hours," notes Pettit.  This space research is fundamental research in fluid physics.  By taking out the parameter of gravity you essentially make a 3D system into a more 2D system.  Surface tension outta this world.......

1960's Surface Tension Video

Yes understanding of surface tension is that old but there is still stuff to learn. If there was not new stuff to learn and explore this blog would be useless. This video is from the 1960's. He does a lot of really cool experiments to give the audience a good idea of surface tension. Mostly, I love how this guy is wearing a suit and starts smoking half way through the video. It is very Mad Man-esque.

Part 1



Part 2

How a housewife changed the world!!

This morning I was talking to a colleague of mine about hobby scientists. People at home that buy a microscope, people that find some interesting physical phenomenon and post on youtube using their LCD displayed smartphone, or the many astronomers looking to the sky to find solar bursts. Science can be found everywhere around us like in the night sky, out in our backyard and even in our kitchen sink. What better place to discover science than your kitchen sink?

A German woman and independent scientist, Agnes Pockels, did just that in 1890. Legend has it that doing the dishes in her own kitchen Agnes discovered the influence of impurities on the surface tension of fluids. So she set out to measure these surfactant impurities (different oil from cooking) and started experimenting. To measure the tension she developed the Pockels trough, precursor to the Langmuir scale, and published the first stearine acid. She wrote to Lord Rayleigh a scientist at Cambridge (who discovered Argon which later won him the Nobel Prize) shortly after he published initial suggestions that oil might form a monolayer on water.

In this letter she described an apparatus she had designed to measure the surface tension of monolayers of hydrophobic and amphiphillic substances. Agnes made a simple trough from a tin pan with tin inserts to determine the size of a surface. She had a balance on one side with a 6 mm disk to the measure the force required (e.g. the surface tension) to pull the disk from the surface. With various oils she hand around the house she described the behavior of surface tension. She added to this by calculating the amounts of material required to form a monolayer and commented on the purity and cleanliness required to accurately perform measurements of surface tension. She also reported the thickness of the film of the of various amphiphillic substances on the surface of water. Quite extraordinary for a housewife. The paper was published in Nature!!

Now monolayers and Langmuir-Blodgett troughs (they later modified Agnes Pockels' home built trough) are used to uncover many fascinating discoveries. For example they are used to fabricate nanoscale electronics using materials like graphene, understand how drugs permeate into the blood brain barrier, or fabricate LCD (liquid crystalline display) for your smartphone. So the next time you pick up your smartphone think about Agnes Pockels and try not to drop it in the sink.

Surface Tension In Brief

I did not really explain what surface tension is. Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with gas, acts like a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air). If the surface is between two liquids (such as water and oil), it is called "interface tension."

What Causes Surface Tension?

Various intermolecular forces, like hydrogen bonds and Van der Waals draw the liquid particles together. In brief, surface tension arises from the strong interactions between water molecules through these interactions. However, you get a better appreciation of the magic of surface tension if you understand the bonding. Two Hydrogens (hydrogen bond donor) are attached to an electronegative oxygen (hydrogen bond acceptor) covalently. However other bonds called hydrogen bonds are between each water molecule. The hydrogen bond (5 to 30 kJ/mole) is stronger than a van der Waals interaction, but weaker than covalent or ionic bonds. The hydrogen bond is described as an electrostatic dipole-dipole interaction but has some features of stronger bonds like covalent bonds. Liquid water is specials since for every water molecule can be H-bonded to four water molecules. It is this strong interaction which also manifests in the other unusual property of water, its high boiling point, melting point, and viscosity compared to otherwise similar liquids.

As mentioned each water molecule can make up to four H-bonds but this only occurs in the bulk of a liquid. (Water basically likes to hang out in a gang). On the surface, however, the interactions with the neighboring molecules are limited and weaker, resulting in a higher free energy and reduced intermolecular hydrogen bonding of the molecules. Surface tension thus finds how strong these hydrogen bonds on the surface are. is. This interaction on the surface can change with temperature or if you put a surfactant like soap into the medium...

Surface Tension Man

Climbing walls just got easier with surface tension and some brains. A palm-sized device was made by researchers at Cornell which uses the combined surface tension of a series of minute water droplets to create a strong adhesive force. Using an electrical field to pump the water through the holes, he can also reverse the process, allowing the plate to become unstuck on demand simply by changing the electric field. So climbing walls just got easier and you may not need to be bitten by a radioactive spider.

See the full Telegraph article.

I hate belly flops

Watching this video makes me cringe!!

Everybody has probably belly flopped at some point so they are probably doing the same face as I am right now. But after watching this video I am wondering why the water was such a hard landing.

Two factors play here: the compressive strength and the shear strength. The compressive strength (and oppositely the tensile strength which is related to the surface tension) of a material like water depends on the molecules. The shape of water molecules determines how they line up (or don’t line up) when under pressure and compressed to move closer together. Atoms in a body of water will try to find an equilibrium position and distance themselves throughout the material (in this case the ocean) to return to equilibrium. The compression strength is what makes the belly flop hurt and makes me cringe. Compressive strength is measured in dynes/cm2.

The shear strength is like the shearing force or rigidity. Shear strength is measured in dynes/cm2. Water has zero rigidity. Like if you were to turning a round jar of water with a fish in it--the jar turns but the water does not, and the fish is still facing the same direction. This is because the sides of the jar slide across the water without affecting it--water has no shear strength. Put gelatin in the jar and you have a material with shear strength--and the fish will turn with the jar (do not try this at home). In the case of the belly flopper, since he jumped with his whole body parallel to the plane of the water he confronted the in-compressibility of water mentioned above.

If the guy in the video were a better diver like lets say David Hasselhoff in Baywatch then perhaps it would have looked better. So the next time you dive in water you put your hands in front to break the water, and, if you do it right, you slide right into the water without pain--again because water has no shear strength. You also displace as little water as possible making less of a splash. Diving like this would make me cringe less.

(Some info was found here in this great explanation of seismic waves).