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Science

We Finally Know Why Oil and Water Don't Mix 222

Posted by timothy
from the they-split-over-demi-moore dept.
CoveredTrax writes "Everyone knows oil and water don't mix. It's a simple concept, sure, but the hydrophobic interactions between fats and water are crucial to the mechanics of microbiology. The weird thing is, the base theories of chemistry suggest that there's no reason oil and water shouldn't mix, even though it's obvious that's not the case. Now there's an explanation: a team of chemical engineers at the University of California, Santa Barbara have defined an equation that measures a compound's hydrophobic character. It's the first such equation of its kind."
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We Finally Know Why Oil and Water Don't Mix

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  • Huh? (Score:2, Insightful)

    by Anonymous Coward
    I read TFA, and I still don't know why oil and water don't mix. Frankly, I don't think these researchers do, either. They seems to have come up with some kind of empirical formula that describes the interactions without really understanding why they are happening.
    • by Hatta (162192)

      That's what science does. It describes the way things behave. "why" is an invention of the human mind. It's not cromulent to expect a scientific answer on "why" things happen, they just do.

      • If science didnt believe there was a "why", it wouldnt bother with experiments in the first place. The why is what we are generally after-- what is the cause?

        • Funny, I always thought that science was about reproducibility

          • by JustOK (667959)

            sometimes it is about things that are not reproducible.

          • If it is reproducible then we ideally have the "why" down or can tweak till we see the variable that leads to "why". You could have "Why" in experiment 1, but you need at times up to experiment 100 to be sure that "why" is not "interesting glitch".

          • Reproducibility implies an unchanging cause, that is, a why. If there isnt a cause to something, you will be unable to reproduce it.

          • No. Science is about making a falsifiable hypothesis and then making observations to determine if the hypothesis can be falsified. For example, astronomy is a science, but it lacks reproducibility and experimentability. It is purely hypothesis and observation.
            • Science is fundamentally about learning things. What you described above is one of the methods we use.

        • by Hatta (162192)

          Scientists may be out to find a why, but it only exists in their minds. "How" and "what" are all that really exist, anything more is anthropomophizing the universe.

          • by jpapon (1877296)
            So you're saying causality is a creation of the human mind?
            • You would be surprised at how many armchair scientists would declare causality to be simply a figment.

            • by digitig (1056110)
              Some scientists seem to be saying something along those lines [postbiota.org]. But separating the how and the why doesn't necessarily do that. In popular usage "why" has multiple meanings. When scientists exclude "why" explanations they're just using one of those popular meanings; they're actually excluding teleological explanations, but most folks are happier with words like "why" than with words like "teleological".
            • Causality in science is an assumption. [wikipedia.org] You can also refer to the Axiom of Causality. [wikipedia.org] So yes, causality is a creation of the human mind.
              • If we stop assuming causality, how on earth do you go about setting up experiments? You would have no reason to believe that you could POSSIBLY reproduce anything, if effects are simply random occurrences.

                • If we stop assuming causality, how on earth do you go about setting up experiments? You would have no reason to believe that you could POSSIBLY reproduce anything, if effects are simply random occurrences.

                  That's exactly right. Not assuming causality is no impediment to scientific inquiry -- ask any grad student studying quantum theory, if you don't want to take my word for it. You should read How the Laws of Physics Lie by Nancy Cartwright, a professor of philosophy at the London School of Economics. Her theories on causal inference and objectivity are the direct result of her inquiry into the nature of quantum mixture states and this book is a standard text for students of the philosophy of science. Yo

              • Having read that article, I would add, it says a "basic assumption"-- that is, a foundational assumption.

                Every bit of knowledge and observation we have is fundamentally based on a set of assumptions; without them you would be left doubting everything, including your ability to doubt and your very existence.

                • Having read that article, I would add, it says a "basic assumption"-- that is, a foundational assumption.

                  Every bit of knowledge and observation we have is fundamentally based on a set of assumptions; without them you would be left doubting everything, including your ability to doubt and your very existence.

                  Hmmm, I think you need to re-read your Descartes, especially the first, second, and third meditations in Meditations on First Philosophy. You can doubt everything, including the act of doubting, but you can't doubt that you are actually *doing* the doubting, so you must, therefore, exist. From that first philosophy, via the famous Cogito Descartes establishes Dualism, which survived in one form or another for three centuries, until it was thoroughly demolished by Dennet, Serle, and Churchland around the

            • by spazdor (902907)

              In many people's parlance, causality is a how question, words like why are reserved for talk of things like intentionality and purpose.

        • Re:Huh? (Score:4, Interesting)

          by rufty_tufty (888596) on Thursday October 13, 2011 @10:29AM (#37701418) Homepage

          Not really.
          Does gravity work because mass distorts space or because of gravitons? At the heart of it most science doesn't care why, but it does care what.
          Now theories are proposed to postulate a why, but they're usually used to encourage more experiments.
          Many of the previous whys have been proved wrong, or at least incomplete, bohr model of the atom Newton's universal gravitation, any theory of superconductivity; but it doesn't matter the experiments and results were real and the ideas produced by the models useful.
          Can't remember who said this, but Asking why we do science is like asking why we have sex, sure sometimes something useful comes out, but that's not the reason we're doing it.

          • Re: (Score:2, Interesting)

            by Anonymous Coward

            The answer to "why" something is, is that God did it. All the time. Every time.

            At least according to my grandfather. An overly simplified conversation regarding such went like so:

            Him: Helium rises because God did it.
            Me: Helium rises because it is lighter than the rest of our atmosphere.
            Him: Why is it lighter?
            Me: It has less mass.
            Him: Why does it have less mass?
            Me: Because it does?
            Him: So you admit that God did it.

            • Re:Huh? (Score:4, Insightful)

              by maxwell demon (590494) on Thursday October 13, 2011 @11:36AM (#37702268) Journal

              Well, I wonder how he would have coped with the following:

              Him: Why is it lighter?
              You: Because it has fewer nucleons.
              Him: Why does it have fewer nucleons?
              You: Because otherwise it would not be Helium.
              Him: Why would it not be Helium?
              You: Because we humans defined Helium that way.

              • by lawpoop (604919)
                That makes it sound like humans define things into existence, and create their properties by declaring them.
            • Your grandfather isnt arguing that there arent natural causes; he is saying there is an initial cause at the beginning of it all.

              In apparently trying to ridicule him, you show your own failure to comprehend what he was saying. I would also note that ridiculing ones grandfather is hardly something to be proud of doing, especially in front of everyone on the internet.

          • Does gravity work because mass distorts space or because of gravitons? At the heart of it most science doesn't care why,

            Those ARE the why. Asking "why" is asking "what caused the phenomenon in question". If its because of gravitons, the gravitons are the why, the distortion is the what, and so on.

            Im not sure if we have a simple failure of communication here, or if people dont understand the definition of "why", or if people are actually denying causality.

            • I take your point, but i don't think science is that simple (it never is, but that's it's charm).

              I've tried to write a point below but Feynman explained it far better than I can: http://www.youtube.com/watch?v=wMFPe-DwULM [youtube.com]

              The why of Newtonian gravity is that mass attracts other mass proportional to the two masses and that attraction falls off with distance by the inverse square law.
              Why it does that could be spacial distortion of relativity or it could be gravitons or it could be a new model we have yet to co

          • by Mab_Mass (903149)

            Does gravity work because mass distorts space or because of gravitons? At the heart of it most science doesn't care why, but it does care what.

            No, it is engineering that really doesn't care about why. Steel is stronger than wood, which is why we build big buildings out of steel and not wood, but to make a building, we don't need to understand why, only how it behaves.

            Science is all about explaining why something happens. If someone could determine, conclusively, the mechanism of how gravity works, th

          • http://www.youtube.com/watch?v=Dp4dpeJVDxs [youtube.com]
            -Richard Feynman

            Hands down the best response to "why" I have ever heard.

        • Re:Huh? (Score:5, Insightful)

          by Kjella (173770) on Thursday October 13, 2011 @11:01AM (#37701842) Homepage

          Well there's two meanings:
          Q: Why does the apple fall to the ground?
          A: Gravity

          Q: Yes, you've named the force and given me a formula to calculate it but why does the apple fall to the ground?
          A: We don't know, and even if we ever find something more fundamental that explains gravity, then that again won't have a "why".

          Science explains the "how", when you derive it from other things we often say "why". But if you want turtles all the way down, there's no "why", no reason the universe is this way and not some other way. It's purely descriptive of the way it is.

          • by Hatta (162192)

            Thanks! That's a really clear way of getting across what I was trying to say.

          • Q: Yes, you've named the force and given me a formula to calculate it but why does the apple fall to the ground?
            A: We don't know, and even if we ever find something more fundamental that explains gravity, then that again won't have a "why".

            Which is how science works, and what it is all about. If we had no desire to climb further up the chain in causality, we would never do experiments.

          • > Science explains the "how", when you derive it from other things we often say "why". But if you want turtles all the way down, there's no "why", no reason the universe is this way and not some other way. It's purely descriptive of the way it is.

            Yep. But as you begin to see the next turtle down, you get a better description of the turtle you are clambering over. We get "how"s in the process of explaining the "why"s.

            "How" begets engineering.
            "Why" begets science.

          • In other words, we really don't "know" anything new, we just added more descriptions to the undefined without really explaining what the undefined is. This didn't explain "how" it worked either, it just showed that using the formula, "it works".

          • > A: We don't know, and even if we ever find something more fundamental that explains gravity, then that again won't have a "why".

            And that's total nonsense. Science _assumes_ that there is no answer to this question, that it is not attainable, and not knowable. The problem is, Science is incomplete: is is _unable_ to answer these types of questions so it it hand-waves them as being "unimportant."

            Science: Answers "How". Ignores Why.
            Religion: Tries to answer "Why" but fucks that up even worse by using i

            • by Kjella (173770)

              The problem is, Science is incomplete: is is _unable_ to answer these types of questions so it it hand-waves them as being "unimportant."

              Not unimportant, just that it is impossible to narrow down the possible explanations. Each religion tends to give one answer, but none can be shown to be right and the others wrong. If anyone is handwaving, then it's the religions trying to prove what can't be proven.

              That said, most of the world religions do make claims in their religious tests that can be scientifically tested and proven wrong. Unfortunately there's a whole lot of unscientific explanations for this, including "This text is an allegory", "I

        • by ShakaUVM (157947)

          Science deals with How stuff works, not Why stuff works. Ten million books on "Why does fire burn?" notwithstanding.

          Why just takes you one level down, and will eventually reach a level called "I dunno, the universe just works that way."

        • If science didnt believe there was a "why", it wouldnt bother with experiments in the first place. The why is what we are generally after-- what is the cause?

          Nonsense. Priests and shaman want to tell you "why' something happened, scientists will only tell you "what" happened. "Why" questions are not scientific -- because to even ask a "why" question requires faith that there exists some kind of meaningful answer in the first place. Faith, by definition, is irrational, so "why" questions are, by extension, also irrational. A scientist, on the other hand, will tell you only "what" happened, and he will insist that he tell you what the error bars in his observ

      • "Just because" is not an excuse I've ever heard a scientist use. In any case, I think OP actually has something; the discovery is a measurement of what's happening, not an explanation. It seems they still don't know why fat and polar compounds interact the way they do, and in fact are still baffled, because they see no reason for them not to interact normally rather than repel each other. However, we can now measure to what degree it occurs. Anybody want to correct me or clarify? I'm actually pretty interes
        • by Mab_Mass (903149)

          I had exactly the same response to the article - they've created a mathematical model the reflects what they observe, but they still don't really understand the mechanism. Looking at the comments of the article, I found a link to the original article [pnas.org]. From what I can understand (by reading the abstract), it sounds as if the work was (surprise) a lot more complicated than the article linked above. From the abstract:

          A quantitative and general model is derived for the interaction potential of charged bila

      • by nomadic (141991)
        Have to add my disagreement here; science is all about the why. In ecology and biology textbooks you'll sometimes see equations like this ("this formula is based on empirical observation") but the authors are typically very careful about distinguishing it from the rest of what they present, and usually describe it in an embarassing tone ("we really wish we knew why this formula works, but for the present moment all we do know is it does").
    • I actually thought they did mix. I remember a story a few years ago that said the only reason the wouldn't mix was because of impurities, so ultra-pure oil would mix with ultra-pure water. They had ideas about environmentally-friendly cleaning products.

    • by BlueCoder (223005)

      I don't understand everyone eases responses. The summary said why. The actual article didn't. The summary should have said scientists for the first time have an equation to describe the behavior.

      When are we going to have a rating system for submitters accuracy and as users of /. be able to filter based on quality and accuracy?

  • Entropy (Score:5, Informative)

    by vossman77 (300689) on Thursday October 13, 2011 @10:08AM (#37701170) Homepage

    As I teach in my biochemistry class it is entropic cost of not separating them that causes their separation, but I have yet to really wrap my head around this study. Nonetheless, here are some links to the original research:

    * Abstract: http://www.ncbi.nlm.nih.gov/pubmed/21896718 [nih.gov]
    * PNAS (paywalled): http://www.pnas.org/content/108/38/15699 [pnas.org]

    • Re:Entropy (Score:5, Interesting)

      by digitalderbs (718388) on Thursday October 13, 2011 @12:14PM (#37702762)
      I'd like to add a few points to this useful post, as a related expert.

      As implied by the parent post, one of the biggest reason scientists care is because this is a dominating contribution to the folding of soluble proteins--proteins in water. The hydrophic effect has been understood for a long time (half a centery), including the fact that the entropic contribution to the free energy is proportional to the surface area change between two separate oil droplets and one. (This is the a-a(0) term in their equation.)

      Their equation further adds contributions for the surface tension of the solvent (gamma) and an exponential decay term for the drying of water between the two two hydrophobic surfaces are they approach each other. Such phenomena have been well characterized in the last ten or so years by molecular dynamics simulations, and this appears to be an experimental confirmation of this effect.

      The statement, however, that this paper finally describes the enigmatic hydrophobic effect is a gross PR overstatement.
  • I read TFA (Score:4, Insightful)

    by bryan1945 (301828) on Thursday October 13, 2011 @10:14AM (#37701226) Journal

    And basically it says van der Waals' theory is wrong, and here is a new equation. That's pretty much it.
    Anyone who knows about this stuff want to take a look at the equation, and see if it makes any sense? Not my area.

    E(D)= -2i(a-a)e^(D-D)
    where:
    E = energy
    D = distance
    a = area of molecule

    • by bryan1945 (301828)

      Oops
        -2y[sub i](a-a[sub 0])e^(D-D[sub 0])
      Forgot /. doesn't like weird characters.

      • by mcgrew (92797) *

        I always wondered why a nerd site would make it so hard to post any equation more complex than 2+a=b. It's also weird that math symbols aren't part of the ascii character set.

        • the first is not bothering to sort out a decent subset of Unicode that is "safe" to use (there are control characters and other nasties in unicode).

          the second is simply lack of space in 255 characters when you have to get drawing characters also

      • I really wish /. had proper unicode support, and MathML or similar.

  • And here I thought it was because they are more attracted to each other than they are to other types of compounds, ie water strongly hydrogen bonds to itself, squeezing out any hydrophobic molecules, while long hydrophobic chains stack strongly, squeezing out anything that doesn't stack strongly.
    • by TeknoHog (164938)

      I thought this too. Another practical reason is that the two liquids usually have different densities, so one will tend to float on top of the other.

      I'm not sure about the stacking theory though. Long-chain molecules are not exactly straight, at least when in the liquid phase. If they were to stack neatly with each other, you would get a crystal. My impression is that polar interactions are generally stronger, so it is mainly water that squeezes out any non-polar intruders.

      • by Arrepiadd (688829)

        Another practical reason is that the two liquids usually have different densities, so one will tend to float on top of the other.

        You mean like alcohol and water? Or like typical gases dissolved in water?
        The "one floating on top of the other" is a consequence of them not being miscible, not the other way around.

        • Miscibility and solubility are distinct concepts. Alcohol and gases DISSOLVE in water. They are not miscible in water. Oils are not soluble in water but that doesn't mean that the two couldn't exist in mixed phase with the more dense water suspending droplets of oil (emulsification). The three independent factors of insolubility, imiscibility, and different densities explain why you get two distinct liquid phases with oil floating on top. No one of those three factors explains the other two, though.

    • by digitig (1056110)
      I thought it was because one ran Linux and the other ran MS Windows.
  • If you carefully put oil on top of water, you realize it "swims" as it is lighter than water.

    Now if you shake it, your might expect it could "mix" with water, like alcohol e.g. does.

    Now you have to understand that there are different kinds of "mixes".

    Alcohol in water is a kind of solution, like salt in water (albeit looking closer at it, there is a significant difference).

    However, oil in fact does mix with water pretty fine if you can make the oil into very small droplets.

    Milk e.g. is an emulsion of water a

    • Re: (Score:3, Informative)

      by cmacdonald (2484050)
      Right, but try and use those sentences to predict and calculate the magnitude of those forces. How is that going? The reason this seems to be significant is it allows us to model these forces beyond the the explanation of "the oil sticks together". Van der waals forces don't apply accurately here so we don't have a good tool to calculate these things. From the actual publication: "A quantitative and general model is derived for the interaction potential of charged bilayers that includes the electrostatic
      • by pclminion (145572)

        Right, but try and use those sentences to predict and calculate the magnitude of those forces. How is that going? The reason this seems to be significant is it allows us to model these forces beyond the the explanation of "the oil sticks together".

        The headline is "We finally know why oil and water don't mix" which seems to suggest that what has been discovered is more profound than just an improvement in accuracy of calculations. It makes it sound like humanity is a bunch of idiots going "Derrr, the wate

    • Just being pedantic, but homogenized milk is an emulsion; milk out of the cow most certainly separates into milk and buttercream (and the buttercream itself is a high-fat emulsion; it still has a lot of moisture in it.)

      If you could explain it away with polar bonds (or lack thereof), why do emulsions emulsify? The hydrocarbon and water molecules have the same number of bonds, and the same density, no matter how vigorously you shake them.

    • by Mab_Mass (903149)

      Your post addresses some of the basic understanding, but it is more complicated than you paint it. After all, if it wasn't why would there still be a lot of research into it? Consider this thought experiment:

      You have a large solution of water with 3 oil molecules floating around inside of the water. Eventually, these 3 molecules bump into each other and stick. By having these two molecules start acting like one, there is a relatively large entropic penalty to be paid, and our understanding of a lot o

  • I have no background in this area, but I'm surprised to learn that we didn't know this already. Makes you wonder what other "simple" discoveries are waiting in around the corner.

    • by Mab_Mass (903149)

      How about the fact that we don't fully understand liquid water [chem1.com]?

    • How friction works

  • > the hydrophobic interactions between fats and water
    > are crucial to the mechanics of microbiology

    Also, salad dressing.

    • by idontgno (624372)

      I am reassured that although we now understand better the molecular interactions between top-grade extra virgin olive oil and an extravecchio balsamic vinegar, the mysteries of the delightful concoction created by forcibly mixing the two are still untouched.

      Explain a good salad dressing down to the quantum level, and it will still be good beyond human comprehension.

  • ... what would the gulf oil spill have been like if oil and water did mix?

    • by jfengel (409917)

      Like dark gray mayonnaise.

    • If oil and water DID mix, the total volume of oil, which would have dispersed over the massive body of water that is the Gulf of Mexico, would have been a rounding error. There would have been some localized effects, but not catastrophic ones in any way.

  • Old news -- maybe you youngsters can't remember:

    yes they do [newscientist.com]

  • a team of chemical engineers at the University of California, Santa Barbara have defined an equation that measures a compound's hydrophobic character. It's the first such equation of its kind.

    Perhaps there's an escape via language lawyerism via "of its kind" but for decades there has been software to estimate the hydrophobicity of small molecules and (relying on even more approximations) proteins. Underlying that software are scores of "equations" that use tables of atomic and molecular fragment parameters of electronegativity and polarizability to calculate 'not bad' estimates of molecular hydrophobicity.

    And while i'll quibble about "the first such equation"; i really think most folks shoul

  • by snoop.daub (1093313) on Thursday October 13, 2011 @12:12PM (#37702726)

    I work in the field on the theory/simulation side, and have actually had dinner and discussed research with Dr. Israelachvili a couple of times. I've only had a chance to skim the paper, but I think I can summarize it pretty well... by the time I've really absorbed it you folks will have moved on to the next shiny new story so I'd better do it now!

    First of all, the report claims that the paper is all about how oil and water don't mix and makes a big deal about how we don't know how that works. For simple stuff like say water and a basic hydrocarbon like octane, that's really not true... it's all about what has already been said above, polar vs. nonpolar (electrostatics) and entropy.

    Things get more complicated when you want to model something like an extended hydrophobic surface, or the interactions and formation of bilayer membranes like we have in a cell. It's been known from experiments since Dr. Israelachvili's work in the 80's that if you take two such surfaces (usually mica functionalized to make it hydrophobic) and bring them together in water, they will repel each other, up until at some point they very quickly strongly attract, expel the water between them and glue themselves together (also called "cavitation"). This is the sort of data shown in Fig. 2 in the paper. The connection with membrane formation is to describe how two membranes behave when they come close together, they have to do something similar to get close enough to fuse (figure 3).

    Figuring out how to describe this behaviour from a theoretical standpoint has been very difficult! We know what all the parts have to be (hydrophobic,electrostatic, steric/Van der Waals, entropic) but haven't been able to put them together in the right way to describe all of the experimental data. What Jacob and his team have done here is found a nice way to 1) describe the hydrophobic interaction between extended surfaces mathematically (the equation above), 2) combine it with all the other parts (figure 4), and 3) show that the equation with a combination of fitted and measured parameters can fit the experimental data pretty well (Table 1). It's very nice work, definitely a step forward in our knowledge of hydrophobic surface and membrane interactions, and I'm going to make sure I study it more carefully soon!

    • Thank you. Could you explain 'mica functionalized' a bit? Hooked to something? Google wasn't particularly useful.

      (This is why I deal with the noise on Slashdot. Sometimes the signal gets through).

  • The weird thing is, the base theories of chemistry suggest that there's no reason oil and water shouldn't mix,

    Huh? I thought oil and water don't mix because oils have primarily non-polar covalent bonds vs the ionic bonds in water molecules? That's what I was taught, and a quick google finds that this appears to be the generally accepted answer.

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