Public Lecture—Water: The Strangest Liquid

okay now another thing that happened to me tonight is that two minutes ago I was told that I had to introduce the speaker so I just interviewed him but but I've known him for a while so I can kind of do it okay it's a great pleasure for me tonight to introduce professor Andrews Nielsen professor Nielsen works at SS RL where as the place where we make all this synchrotron radiation that he will talk to you a little bit about professor Nielsen got his PhD at the University - upsala is from Sweden he's been at SLAC for nine years but he's still a guest professor at the University of Stockholm and he travels back and forth all the time you're lucky to get him tonight what are you leaving anyway next Saturday is going the other way his specialty is fundamental research using sigma tron radiation he particularly works on problems that they just talked about at the State of the Union speech so you have a hard time to follow that speech and energy and environment he's an experimentalist and he works with x-rays and one of his main interests is the chemical bond the thing that keeps molecules together sometimes they separate sometimes they marry sometimes he divorce right but that's the bond right so he's going to explain to you by the way I hope you all wash you hands tonight was water because he's going to tell you what happens when you do that so you have the title there what are the strangest liquid meanders thank you okay y'all hear me UDOT use your forms yes please turn off your phones so it's a pleasure for me to be here today and also it's a pleasure to see all of you here today and I hope you will go out of here actually unreal II understand a little bit more about this miracle liquid I'm going to talk about that I call here in the title it's it's a really strange liquid but I hope at the end here you will actually see that it's not strange it's actually rather special in these special properties could we turn down the light a little bit so what I'm going to describe is actually how we can understand that's too much so what I will describe is actually how we can understand these rather strange properties of water what I mean is strange is that they are unusual and different from almost other liquids most other chemical compounds how we can understand it in terms of the molecular structure and I will kept trying to keep this honor on the level that most of you should actually bathe whenever you have a scientific background or not be able to understand and you're most welcome to ask questions about it afterwards so let's introduce water a little bit and why is water important for us and I think this is a picture that most of you have seen before it's the blue planet is actually the picture from Apollo 11 from space taken towards the planet Earth and as you can see the planet Earth is a blue planet and in this blue because we have all water so much water on earth and everything we do here on earth has to do with water it is the key chemical compound for our existence we know that each human being is probably of the order of 60 between 60 to 90 percent actually contain water the newborn baby has a proof has something happened here I have to give a public lecture though it was a good reminder so we are all made a worker and it's interesting in a way when when people actually looking at life from other planets or thinking it could be other life forms out in the universe they actually first look if there could be water and particular water in its liquid phase not in I like eyes or in the gas phase but in the liquid phase so water is something very very special and it's the basis of actually why we are here and we actually exist here as a human form it's of course unique for all biological life not only we as humans is also unique for plants animals everything and it's also pretty much involved in controlling our climate involved in erosion weather everything has to do with water first also I like to show that we also actually have some appreciation of water ice show this beautiful waterfall here at the border between Argentina and Brazil and here's another picture here in California of Lake Tahoe and there is another aspect of water that I think we all appreciate in a way we always all drawn to water water is beautiful for us we like often to relax taking a bath and I myself personally I'm very drawn to water I try to go a couple of years a couple of times per year actually go in and swim the dolphins in Hawaii I love to be out there playing with them in the water so we actually in in a way are finding water something very special and unique to us so there are other issues with water this is a picture actually I took from Al Gore's movie inconvenient truth that I'm sure many of you have seen and something that is a little bit let's say uncomfortable or scary for us for the future is whether we will actually will have access to clean water so with the climate change water the access of water will be one of the major challenges with respect to the climate change I've ever water could actually be also part of the solution so here is here's a picture of we might actually make energy out of using sunlight and water and here's down here is a quote from Jill van who was a very famous French author in the 19th century he wrote maybe one of the first science fiction water and he said that I believe that water will one day be employed as fuel and as the end of this water will be there coal of the future so this is a this is a picture you know which actually demonstrate how we can use sunlight together with water and the sunlight the energy that comes from the Sun will then split water into hydrogen and oxygen and we will then use the hydrogen as a storage we will store hydrogen in our car for instance if you use this for the transportation as a fuel and then we actually will put the hydrogen into the fuel cell and combine it again with oxygen to make water and then the energy is released that we put in from the Sun and then we actually in that sense we can drive the car on the energy coming from the Sun so the water a lot of research attention now and maybe we will have something like that to come in a decade or two if this really going to work so this could be a future really development of using water also for other energy purposes but the focus today is really to talk about why water is weird or strange everybody knows that water is h2o but what is it something special about this h2o and I'm going to describe a couple of properties that water has which is quite unusual and the first one here it shows an iceberg floating in the ocean and this is as I show here as a tighter water is dancing and ice it means that the liquid has higher density than the solid nearly all other chemical compounds is the other way around as you free something it shrinks it's become smaller here is the opposite as you actually freeze it expands many of you probably have that experience which I had as a kid or even as a teenager where you try to cool sooner or a beer in your freeze and you put it in there you forgot about it and it's all actually the glass exploded and it's because there then the ice actually expanded when it froze in into ice so this is a very very strange property normal liquid I took us a few example here like alcohol gasoline or anything behaves it the other way around that when you freeze it it's rings this is an interesting property also because it actually shows the possibility for how life could evolve on planet Earth this is one part of the key because as water freezes it will float on the ocean and it will in this way form actually an insulating layer and if water would instead freeze where they eyes will have higher density it will freeze from bottom up most likely marine life could have not evolved in the oceans if that would actually be in the property that we will actually freeze the ocean bottom up another unusual property is the density maximum is a little bit more subtle in a way maybe to see for you I don't know how many have actually done this little experiment if you take a glass of ice water and you put a thermometer in it and then you measure the temperature of water at the bottom of the glass you're going to find that it's actually all is going to be 4 degrees Celsius and why is that 4 degrees Celsius it has to do with that we have what's called a density maximum that they water at 4 degrees has the highest density so here is a plot so one of this diagram I'm going to show so this axis I show temperature in centigrade and here is a density a receiver a small variation in density this line here shows a normal liquid which could be like gasoline or alcohol or ether or any other type of liquid and as you can see as you cool cold the liquid the density goes up and you can understand it very simply by as you cool something things doesn't move around on the atomic level so much and therefore becomes small drinks that volume gets smaller and smaller but look at water actually it behaves like a normal liquid in the beginning here but then it's not to deviate and then at one point we reach a maximum and that maximum is at 4 degrees and then it's actually start to go down as you can see here is even plotted that you can look at water below freezing and it's very special property also water has is that you can supercool it you can actually cool it below freezing without actually it's forming an ice crystal you just have to have very clean conditions to do that but that's not the important point it is this density maximum so if he is not now think that we have eyes so ice has a lower density we melt ice into liquid water the density goes up so they the whole thing rings so now after the melting point at 0 degree Celsius we continue to heat the water and it continues to shrink up to this density maximum very very strange so why is this important in a way so also as I talked about the ocean it it means that the water at four degrees is the water that is most heavy because it has the highest density it will always sink down in the ocean to the bottom exactly what you see here in the glass that we have four degree at the bottom the consequences of that is that it's very difficult to freeze a lake or ocean all the way through because as you will generate colder water it will rise up it will always stay four degree below so as Earth has gone through many different climate changes we have had ice times and so on where we had very cool weather still during this time we didn't freeze the ocean all the way through of course you did that most likely up in the polls but we're always going to be water why we didn't do that oh that didn't happen and that allowed marine life to evolve which eventually led to us very very special property of water behaving like this another one which may be a little bit more difficult to understand but let me explain water has a very high heat capacity so what does heat capacity mean it's the amount of heat we need to add to raise the temperature one degree so in order to to therefore raise the temperature of water we have to put a lot of heat or the same to lower the temperature we have to take out a lot of heat so water in this way can store a lot of heat it is good heat reservoir it stabilized the temperatures in the oceans around the world because it will require a lot of heat or taking away heat to lower the temperature and this is actually the reason for that the oceans are stabilizing the climate on earth so here I just show a picture of the Gulf Stream here is Sweden where I come from and without the Gulf Stream Sweden would probably be like Siberia it will be extremely cold and not very comfortable to live that the reason why we can have a rather nice climate in Europe is because we have the gold stream and that brings water that has been heated up down in the Caribbean and then by the current transported up to Europe and it's this heat reservoir which is then caused by the high heat capacity of water that allows that to happen so the ocean carrots stabilize the climate on earth and which is related to the high heat capacity of water another interesting property high surface tension water is the liquid with the highest surface tension so what is surface tension here are beautiful pictures of water droplets and I'm sure all of you have seen this how we could both really form the beautiful droplets and they formed a sphere because they try to minimize this surface area and the minimum surface area you can have is by forming a sphere and that is because of this high surface tension force that allows a lot of water droplets to form like in clouds important for our weather and and in many other circumstances another beautiful aspect of that of the high surface tension is that spiders can actually walk on water I'm sure many of you have seen this and an experiment you can do maybe not with the spider because we should be precious even with spiders although I'm afraid of spiders myself but I love the water and we share that in common with the spider but nevertheless if you just put a little bit of soap in water or you will you can see that actually the spider will sink because then we have lower the surface tension of the water you can actually do this experiment yourself putting a razor blade on the water it will stay there because of the high surface tension one droplet of soap the race of label sink so very high surface tension unique for water if you take you can just take a little bit of oil in your kitchen and you can actually make some droplets and you will put it out out and in your sink or on your kitchen table and you're not going to see beautiful droplet form as you do with water another aspect of the high surface tension is the formation of capillary forces so it works in this way so we have this is like a capillary it can be your straw or a fiber or some some sort of channel here that is formed and the water is has some sort of adhesion here to there to this to the wall of this capillary and that pulls up the water a little bit and at the same time also we have the surface tension here that I actually continue to pull this up so many have seen this as we make the diameter of the straw or the fibers smaller and smaller the rise in the water level goes up and this is this is a result of the high surface tension and the capillary forces so why why is this important it's because this is actually how plants can take out water we can drink water very nicely which I do here Mount but plants take up water via these capillary forces and here's a picture of a redwood tree that we have here in California and actually the water is transported through capillary forces up in this tree with tiny tiny fibers so without this high surface tension of water it wouldn't have any plants if water would be like a normal liquid we wouldn't have any plans so let's now come to maybe the most unusual property but maybe also the most obvious to all of you which has to do with the boiling point of water so it's going to be a little bit complicated diagram that I will try to explain here so here we have the periodic table of the elements I'm not only showing the left part of it and here I have a diagram where I show the boiling point for different liquids depending on the molecular mass and I indicated here with a dotted line have room temperature so let's see now if we take the first look at the chemical group in the periodic table in this case by looking at the group containing carbon and these elements can bind make four bonds and bind four hydrogen atom each of them and what you see now in this plot as we go from an element with higher mass to a lower mass as you see plotted here the boiling point actually decreases all the way down to methane and most of you know methan is like natural gas it's a it's of course a gas and it has a very very low boiling point around minus hundred sixty degrees Celsius so if you now make this similar comparison in there among the elements in the group containing oxygen where we will then form water we will see the same trend as we make them decreases the molecular mass the boiling point goes down and here we have hydrogen sulfide and then the next element with the lighter element is then oxygen and we would therefore expect water to be that if what would have a boiling point of around minus 80 degree Celsius it will be a gas but we all know that the boiling point of water is at 100 degrees Celsius so we could have a liquid so something really strange is happening here and this is the really the first key aspect of water the mystery of water that what is really causing this big change in the boiling point water should really be down here so let me now first explain that a little bit and we even start by actually looking at the both the molecule itself so all know water is h2o and it looks like this oxygen in the middle with two hydrogen atom and we have a sort of an angle here of around 180 degrees we can make different pictures of the water molecule many people have seen this as they go through their chemistry lab and they make these sticks or balls or water molecule in reality this is how a water molecule actually look like so it's nearly spherical it's because the oxygen atom is so much larger than the hydrogen atom it's like the hydrogen atom is a little bit of horns here on the oxygen atom so this is how actually water molecule looks like and how big is it they're actually the diameter is around 3 angstrom angstrom is a unit that we used in the atomic world a lot and I've written down here but that corresponds to in meter so it's a it's a it's a dot followed by nine zeros and then a three so that's how small the water molecule is in its diameter so what makes now water to not be a gas at room temperature and it has to do with some very special bond called the hydrogen bond so let's explain a little bit what is hydrogen bond here again is the water molecule forget about these two lobes yes look at this what is the motor molecule here and you probably all know that there are electrons in atoms and the electrons are the ones that form chemical bonds in this case the chemical bond between the oxygen atom and the hydrogen atom but now some atoms are a little bit more greedy they want to have all the electrons for themselves and oxygen atoms really want to have all the electrons for itself so it pushes the electrons towards it and making actually in that sense the oxygen atom slightly negative slightly charge and since it's taking down the electrons from the hydrogen atoms it making them slightly positive charge so we are getting negative oxygen atoms and positive hydrogen atoms that allows now to form a very special bond where a positive hydrogen atom in one molecule can approach the negative oxygen atom another molecule and they have opposite charges here as you can see and in and they are forming on hydrogen bond through this electrostatic interaction and you can see that the distance here between that hydrogen atomic oxygen atom is nearly twice the distance as you have internally in the chemical bond inside the water molecule you can make a very simple cartoon in this way so I will explain that these negative aspects on these oxygen atom actually are a little bit like protrusion of something of the church sticking out in two different directions like this so the hydrogen atoms here are like the arms on this little guy here and these protrusion are like the field and the neighboring molecule arm can then I attach to the feet forming these hydrogen bonds the hydrogen bonds actually quite a fascinating topic by itself the course they are rather weak they are much weaker than what you have the chemical bonds here or the chemical bonds making a table or anything here in this room very solid so they are much weaker than that but they are strong enough that we actually can form bonds at room temperature in all of a normal condition how are you so to live our lives and this is important also for biology so you probably all know about the DNA which has this double helix the two helix or actually forced together with hydrogen bonds and that's why they also can easily separate and form proteins are folded in many different ways also through the hydrogen bonds so hydrogen bonds I sometimes call it the software in nature that makes nature to come alive we can change things we can form things so that's the uniqueness of hydrogen bond so let's take a little bit more look of what we call tetrahedral coordination I will explain that in a minute because we have this two protrusions here of oxygen charge sticking out or the water molecule on the oxygen side and then we have these two hydrogen atoms so we can form a very very stable configuration in this way so if you look here we have this central water molecule here in the center at each hydrogen atom come through in hydrogen bond bond to another water molecule and on the oxygen side we have these two protrusions here where another water molecule could bond via its hydrogen atom going in and we call this the tetrahedral arrangement and it's because if you look here we have a tetrahedron and in the middle we have a water molecule and at each corner there will be another molecule so making a very simple cartoon again with these little guys you can see the hi here how the hydrogen atoms forming the hands can grab grab to this to the feed of the neighboring water molecules on the oxygen side and on the oxygen side of that guy it can sort of allow other water molecules hand to grab its feet so we are forming a very very stable configuration but each of water molecule could actually coordinate for others and we call this tetrahedral coordination and it's going to be important because this is the building block how we actually form ice this is the molecular arrangement in eyes here's again the centered motor molecule in this tetrahedron bonded to four nearest neighbor if you now started to add what more water molecule around this you're actually going to form something we call hexagonal eyes and this is just how how we I added more and more water molecules and eventually it's going to form a lattice the crystal of eyes looking like this one thing I want you to note already now in this crystal is that it looks to be a lot of in space in the middle here you see its rings for them and there is open space in the middle so in that in that sense more trees or watering eyes is not very compact arranged and you already can maybe tell now that there's something unusually dies in that sense because eyes might not have a very high density because of its arrangement but I'm going to come back to this later on so now it's the question what is water so now I described how the hydrogen bonds are in eyes where you can form it with four nearest neighbor but how is it in the liquid phase and now we're going to discuss that and before I going into that I'd like to make a little bit of a personal point here but I want to talk a little bit about my own research and it's interesting sometimes how you as a scientist can stumble over something when I started to work on water 10 years ago I actually assumed that we understood water perfectly well dick it must be it's such a common thing and we must really understand water and I didn't expect anything unusual and I didn't intend to start the water either I was actually going to look at amino acid the most simple amino acid glycine which I've been studying on the surface this is another my research topic another way is going to studied inside water and we did spectroscopy which I would describe in a minute what it is and in order to understand the data so that lies and I needed to take a background spectrum of water so we measured water and when I saw the data I was so puzzled I couldn't understand what what we saw because it didn't fit with the textbook of water that I have learned in chemistry and in physics and so on as I grew up in my scientific career it looks so strange it didn't fit and this caught my attention then and not only me also before the big team and we are many people working on this since then trying to unravel why this was different and this I actually led now to a development of another picture of water that I'm going to show to you and I also wanted to say that this picture is not established or accepted by everybody although it's an align with a lot of speculation or theories that people have had in the past but it's a controversial issue and it's even been written about this debate that we partly initiated in the newspaper here in the Bay Area because Stanford and Berkeley has opposite or opinion about this and they have written about it like a football game which is will be funny that we have some sort of match going on here so let's now I'm going to describe to you a little bit what with what are the tools I have used to look at water and I'm specialists inducing x-rays and what is x-rays so here is here's just showing the different let's say part or what we call their spec spectrum of electromagnetic radiation and they define something called the wavelength so electromagnetic radiation are waves and the wavelengths is simply the distance between two valleys or the distance between two peaks so for you to just have a feeling about the wavelengths of x-rays we have put it in a comparison where we are with the visible light and here is the size of the wavelength so here's the visible light it's sort of the wavelengths is the order somewhere between a cell and a virus particle we can make the wavelengths longer by going in this direction you make radio waves etc where we have a wavelength even of the size of a house or we could make the wavelengths shorter going into the ultraviolet and then eventually into the x-ray region as you can see here the wavelengths in the x-ray region is matching the size of an atom and that makes x-ray so interesting to use because we can in that that way actually look into matter and understand what the atomic wall is doing many of you probably are familiar with x-rays the you actually go to your medical doctor or or get getting a getting an x-ray or your dentist that is more an image of using the x-ray but here we are talking more using the x-ray to do something magical inside the atom to learn something about nature and what the atoms are doing in nature so let me explain one experiment that we have been doing and this is a very simple picture of an atom is over simplified and many physicists would say oh this is it doesn't look like this but let's stay with this very very simple picture of an atom and here we have a nucleus in the middle and then we have electrons that goes around these atoms and here I'm going to distinguish between two types of electrons we have what I call the inner electrons and these electrons are deep inside the atoms and they are really just around the nucleus like this deep inside and these electrons are only on this particular atom and then we have outer electrons which are in the periphery here of the atom and these are the electrons that are involved forming chemical bonds and this electron can be shared with other atoms in forming the chemical bond so we're going to now do some interesting excitations where we are changing these electrons and we're doing it with an incoming x-ray pulse that comes in here and it's going to add is going to attack this inner electron and actually shoot it away like this so the x-ray was destroyed giving its energy to that electron and was shooting away so let's go back here so we take a do this again here comes the x-ray in we are shooting away it is in real Ektron and now the outer electron feels there is a vacancy is a hole and it drops down and an emission of a light emission of another x-ray photon that goes out and it's really that process in particular I'm going to show you how this outer electron falls into that vacancy with emission of light that we are actually going to look in our experiment and now I'm going to show you some real experimental data that going to address the water problem just interesting enough yes when I was standing here one of my co-workers worker came in with a new diagram and some exciting things of water so this is something that is still progressing so let me show you now an x-ray spectra or water molecule so we have this process now how the outer electron falls in into an inner electron and we get emission of light and here we are plotting the energy of that light in photon energy in the diagram here and I'm not showing two spectrum one from a gas phase molecule and what you can see is that you see only one single peak here from this particular x-ray transition of the gas phase molecule and let me do the same thing for eyes where we are looking now of a water molecule that is bonded to four others in this tetrahedron in this tetrahedral arrangement and then you also get will draw the broad spectrum but mainly one one peak here and as you can see there is a shift between this one and that one's energy position here so this is with no hydrogen bonding and this is where we have a maximum hydrogen bonding because we have four nearest neighbors this looked like the shift is with increasing hydrogen bonding so if we now I took a measurement or water what would we expect to see if you did this now for water so I asked made a hypothetical spectrum here so what I took is actually what I call a traditional picture what most people think about water which is a little bit like you take eyes and you make it very disordered you disorder you move a little bit of the bonds band some bonds change a little bit distance and so on and you make a disorder but it's still rod homogeneous most of the water molecules are still in the rod similar chemical surrounding but there is a distribution of that surround which is reflecting in the peak and you see that position of this is in between they are the eyes and the gas phase because we expect that the hydrogen bonding in water should be a little bit weaker than eyes because the liquid is flowing is easy to moving around then than it then he dies so this is what we expected so when we did the experiment what do we see do we see that no what we see is two things that was quite surprising so two peaks what does that mean could be two different types of water molecules then in the liquid and if you look at it one of the peak is very close to the gas phase and the other peak is close to ice looks like water contains two types of molecules what could that be here I has put up a picture but we could think about it so this peak is draw in this way now with coordination with four neighbors here similar to eyes as you can see here because the position is not too far away from eyes whereas this peak is closer to gas face so it must contain a lot of hydrogen bonds that are missing or distorted in a way so it we have to have two rather different types of water molecules in in very different surrounding I call it very distorted this structure and here strongly eyes like two different types of structures mysterious why do we have two different types of structures why would water shoes to do that and it had can actually has to do with a balance of two different types of interactions that is causing that one is maximizing the bond strength I showed you that eyes like to form four bonds so if we cool water down it freezes it should be the most stable configuration it's when we make the best use of our ability to form chemical bonds some maximum bond strength and this guy here which is much more distorted and lack some hydrogen bonds it has to do something with a high entropy and I'm sure many of you have heard the word entropy which for me I remember where I study physics chemistry at the University and I could never really understand entropy took me many years to understand what that really means and I'm not sure I still understand it it's a really strange charm entropy so let me explain a little bit what is entropy and why that matter why that how that comes in into the picture it has to do with that we actually often make disorder in the system we always go to more and more disorder formally it's it's actually it's more related to in how many different way we can dissipate our energy but in a simple picture it can be like that this let's say we have a room and we could put out a couple of atoms in a very regular form alien award in a corner of the room let's say like in a gas phase and then as time will go by it will actually this gas molecule will coast and diffuse out and fill the whole room and this situation is much more disordered as you can see then this situation here we cannot usually go back from such a situation in a room filled with gas automatically it's not going to be that all the gas suddenly accumulate in one corner of the room so this actually has a higher entropy than this situation here's another picture where we are take we make a pile of bricks and we order it very nicely together and then we could instead make something very disordered and so this will be your higher entropy than this one and entropy becomes more important as we increase the temperature as an interaction in in nature which is why the crystal can melt into liquid with high entropy and the liquid eventually can be your gas phase which even go to the gas phase which even then have a higher entropy so as we increase the temperature we get more entropy and this is what is causing a balance between maximum ism bond or maximizing entropy and in water nature choosing to do that balance by actually giving rise to two different types of species it can be looking a little bit like this so here I show a little bit of tentative motion or water molecules which could be inside the liquid so if you look at this guy here which is having this four nearest neighbor around it the motor molecule is very locked in it has a problem to really move around because it's sitting with hydrogen bonds of this hydrogen to that water molecule and with this hydro Nahum with that motive molecule can make very strong bonds but cannot move very much cannot disorder very much look at this guy instead that has less strong hydrogen bonds and it now can actually move around much freely in the liquid and that gives it rise to having a higher entropy so we see we see these two type of structures in the liquid question is now how are these structure distributed in the liquid are these going to be as molecular fragments sitting next to each other or all they are actually going to be separated on some sort of length scale that's the next question we asked ourselves how could really this look like and let me talk one of other tools that you can use with x-rays I choose show you before what I call spectroscopy where we lift electrons to different electronic levels but you can also do what's called scattering of x-ray it means the x-ray comes in towards your sample and then it's deflected in different angles you call that scattering and that type of interaction is more based on diffraction and interference and I'm sure some of you at least have heard that word of diffraction interference but let me explain how how we do this type of experiment it's called small angle x-ray scattering we have our sample and we have an incident beam of x-rays going through our sample and then we have a detector here that we can detect the x-ray coming through so the direct beam which do not scatter will of course go straight through without an hitting detector but there could be some extra devilishly will undergo some scattering here and this scattering is in a very very small angle that's why it's called small angle scattering you have often the word diffraction where you actually determine atomic position I I'm sure some of you know that but that's going to be a very big angle very large angle where the experience goes out in this direction so what this can do with this very small angle scattering is that if you have let's say some sort of particle or less density difference so let's say you your sample contains some sort of patches or structures here which have a slightly different density than the surrounding and what I mean the density because you think about atomic density for a very in a very simple way so if that would be the situation you can actually imagine that we will have a scattering event of these x-rays but they will be slightly deflected and this part of the x-ray beam will actually in the deflection have a little bit different path lengths then this part of the x-ray beam and if these path length is of the same order as the wavelength of your radiation of the x-ray you can get then what we call interference constructive or destructive interferes I'm not going to spend time to explain that in detail but that's how you can get the contrast in your experiment so here's how an experimental data could look like and down here we have what's called momentum transfer but you can think about very simply an angle and are plotted now the scattered intensity here and if we now consider that we will have a homogeneous water as I just showed you before with this x-ray spectroscopy where most water molecules are in a very similar surrounding that's a little bit disordered broken hydrogen bonds here and there if this is the scattering pattern you will actually expect it just comes from a peak here which goes very high up here it has to do with their scattering from the nearest neighbor oxygen-oxygen scattering and it's just decaying from that schedule since nothing is really happening and when we do this experiment here at the light source that we hear on-site at slack is so something like this so they may measure now real water we actually suddenly saw this enhancement here at very lower angles and that enhancement told us that there are density differences in the liquid something looking like this and the minimum here in a very simple picture the minimum and the shape of this gives us the size of these regions which has a different density and we could estimate that to be of the order of 10 to 20 angstrom at least a unit swedish unit on strim he he was actually one of the first two to describe how you could look at all the different colors let's say of light of white light and so on so he dispersed radiation is from the University where I made my PhD that's why emeritus very well anyway they're all miss from unit I show you before the diameter of a water molecule is the three August receive a sense how big these this size is and it could be maybe containing 5,200 water molecules in here so we have some sort of distribution in the liquid how this to that different type of structure will be arranged and this is maybe you cartoon we don't know the exact arrangement of this but we can envision that you cattle a little bit like this I showed you we have something that is very eyes like and then we had something which is very disordered and this is the one that has this high entropy where the water molecules are moving around much freely then in in the eyes where they are instead much more strongly bound and maximizing the bond energy and so this is corresponding to blue region and this is a corresponding to red region so we somehow how accumulated these type of structures they like to hang out together and these structures also and I like to hang out together so we have some sort of mixture or regions of these different structures in reality these are actually going to be fluctuations so these are not going to be stay but they're going to oscillate back and forth so this region might dissolve into that one and this region might pop up somewhere here so it's going to be a dynamic something is really oscillating around there to describe it lets me make a very simple picture here let's go dancing sorry let's go dancing and I want to make a an analogue e here that we are going to a dance restaurant in this dance restaurant we have tables here where people sit around and they socially interact they actually like to get to get together they like to hang out together so they form strong bonds they like to sit there and around the tables of people dancing around maybe not couples but more let's say like a disco dance you're really dancing around here people are moving around fast sometimes they hook up dancing close together forming a little temporary bond or they are maybe hanging up many of them together temporarily and then moving around here in a very rapid movement so this is in this is then this disordered phase would not face or disordered structure where we actually have this high entropy we are disorder we are moving around and here we are forming these eyes like structures around here where people are connecting and hooking up together instead and socially networking and talking but we also have some people that are sitting on this table and seeing the excitement on the dance floor and it's getting a little bit bored and say I want to go up dancing to four he will leave or her she will leave and someone who has been dancing for a long time is getting tired and take his place instead so we would have an exchange of molecules that is in this type of structure where we are sort of more bonded together with the one who are actually out dancing and our jumping around and have a lot of thermal excitement in the room and as you have seen here indicated that the table makes structures which have a lower density because it takes more space whereas these ones that is jumping around in this disordered fashion can pack together we can make a very crowded dance floor I'm sure some of you have experienced this where your dancing no so close to each other so you could really pack things together when you're here that on the dance floor so let's see what can happen if we change the temperature we do cooling so here we are again the same picture jumping around here what happens now if we actually change the temperature since this is a very excited thermally excited where we put in temperature that caused entropy to go up in the system and this is the type of structure you will have if you will freeze the system but well this structure will then of course be the whole system so if you lower the temperature you're going to form it's like we are creating more tables people a little bit less sited maybe the evening is long and guitar they would filled up more tables more people can sit around so we we will have a conversion as we change the temperature as we lower the temperature we will generate more structures where people are connected calm peaceful sitting there and so as we lower the temperature the bond energy in the eyes like component becomes more important and we convert the disordered structure to the ice like structure so this is the picture in a way or the uniqueness or medical part of water but normal liquid like gasoline or alcohol and so on would not have two structures will only have one type of structure in the liquid phase water is unique forming these two and now will I go back and talk a little bit about these very special properties that water has how can we understand that now what I just showed you so let's take the first one more two dances and this solid here here we have ice and I'll show you before it is tetrahedral bonding where each water molecule is surrounded by four nearest neighbor it generates a structure which has a lot of open space here they're not dominating structure in the liquid which is this disordered structure can avoid to have this open space because you can pack the number of molecules much better together because you don't have so many of these very directional hydrogen bonds so if you take balls spares and put them together and ask how many could how many kind of pack together with spheres you can actually pack together twelve aspheres around the single one that's what we call a closed packing you can immediately realize now that in eyes each water molecule is a surrounded by four that's quite far away from 12 you cannot really pack that close together in is structure but in the liquid phase now when we have this disordered structure we can do that we do need to form this open space that's why we have a higher density in the world in in the liquid phase compared to the solid phase in ice where we generate this open space so we can understand that now why actually this happened and of course most liquid will form more of these twelve nearest neighbor and be rather compact solid form and as you melt that solid form means it's liquid you just going to disordered that type of coordination or twelve around it so it can behave in that way as a normal liquid here the solid instead by making these directional bonds may call this open space and that's why it has lower body and lower density let's take the next property this density maximum that's a little bit more difficult to directly see so again the water glass with the thermo meter we have four degrees of water in the bottom of the glass and applauded again the density here as a functional temperature or the density how it varies as we change the temperature let's go to this picture let's identify how this structure and this structure should change its density as a function temperature all it is said that this type of structure will have a higher density than ice like structure here but we would expect that this type of structure will behave like a normal liquid so as we cool the system down and we look at only at this type of structure then everybody who's dancing the dance a little bit slower and slower and they can compact they can get closer to each other by lowering the temperature that's why the density goes up the same with these eyes like structures as we cool the temperature down may be people sitting around the table at higher temperature is a little bit agitated they are discussing or talking about things and so on and as you cool it down they get more and more calmer maybe it's eventually falling asleep and that of course makes also the table to contract as you get lower and lower temperature so that will also vary in this fashion but it has a lower density that's why the curve is down here comparison to that part so what will happen now as they cool this system when we have these two components so if you look at this picture I only had three tables out here and this picture now we have actually five tables so if I converted some of the dancers into the table so as we cool the system down we will then of course follow in the beginning this normal behavior of a liquid but then in this region when you start to deviate it's because we are creating now space here of these structure which has a lower density and it's that D structure appearing here as a lower density make this now to change around and as we cool with the density goes down although both components should shrink but we convert this structure which has a high density into structure that has a lower density by cooling by converting this into more of God that's actually what makes then this density maximum and many of the properties that you see with water I haven't showed you all of them but many of them actually is related directly to their balance between these two structures that makes water to be that weird just to give you an example of another property viscosity but this viscosity is in a way how easy something can flow high viscosity we can flow it easy what do you think would happen if you have something that can flow and you put pressure on it you will compact it somehow right you would expect that it doesn't flow so well as you put pressure on it so what does it what to do it doesn't behave as it should right so as we put pressure on water it flows easier can we understand that in this picture yes they as we put pressure on water this lower density eyes line is converted into the high density structure and the higher density structure has a has a higher viscosity you have actually altogether 66 but cool anomalies and normal ease is something that is behaving differently 66 all different properties where water behave different than it should let's continue in our list with a high heat capacity and I'm not going to dwell on that very much but it has very much to do with this very disordered structure and how water molecule can move around freely which allows you to give this high heat capacity let me spend a little bit more time on this high surface tension because this is quite interesting in a way that we could form these water droplets and as I told you the high surface tension try to minimize the surface area by making a sphere and this has to do with exactly the same property as I show you that water has a very high boiling point and remember that why did water have a high boiling point because it can form hydrogen bonds between water molecules like this so it's the ability for water to form hydrogen bonds that makes it to have a high surface tension so it makes a lot of bonds between water molecule here at the surface and if you would increase the surface area you need to break some of these bonds and water doesn't like that you want it to all pull together how would that be if you take another molecule let's took yes some big hydrocarbons can be gasoline gasoline is a liquid because it has a very high molecular mass so it has a very high molecular mass it means that it's cannot have so much motion around as a small molecule like water and that's why it's for the liquid at room temperature gasoline but the interaction between the water molecules is very very weak so it's more but if you look at this diagram with a very heavy element you can see you could actually have a liquid of h2 polonium polonium is a very very heavy element because it's just heavy but water is a very light molecule it's the smallest molecule that we have that exists as a liquid and it's only that because of these hydrogen bonds so gasoline is not going to have a high surface tension or any oil you can yes you cannot form really nice droplets as you can do with water molecules so this is really the explanation for why we have this surface tension high surface tension at the end and coming to my end here I like to us to emphasize two particular aspects of water that I hope you have seen here in my in my lecture for you to take home and remember which is important what I've talked about one is the formation of hydrogen bonds that is unique in water making water not being a gas as it otherwise should be course this is the number one property that allows us to be here today otherwise we will disintegrate if we would be all your gas inside right that will be quite dramatic actually turns out that the strengths of this hydrogen bomb at different distances here if you would tweak that strength yes a few percent everything around us everything we are will change exactly how strong that nature of that hydrogen bond is determined a lot of what we see around in our world the other thing I want you to remember is it the dance restaurant and in particular that we actually see two types of structures in the liquid and they are somehow separated in space with certain length scale and maybe this table is actually 50 100 people or buta molecules sitting around it and we have something that is bonded together and they exist because they could really form strong bonds and they are a little bit like ice like but they have a lower density lower density and then we have this surrounding here which are these excited motor molecules that hops around and it's like a dancing forming a disordered high density and the balance between these two is giving a lot of the magical properties of water just however I explained for you the density maximum so for that I like to end by showing some beautiful pictures here water and maybe saying water is maybe not so strange because maybe we can understand why it behaves like this but it's very special and it's unique that it's behaving like this and before I end I just wanted to put up a list a lot of people that has been involved in the work I show you and the funding agency and many different things so I'm not done all this work for myself and that I thank you for your attention and willing to take questions oh that's right that's a tricky question which is probably outside my level of expertise but I could imagine that oh so he asked in a way if you for organ preservation if you into a void crystallization if you could freeze when were gunned down to rather low temperature by applying pressure to avoid crystallization as you know as I said as we crystallized water it will expand and it will destroy the cells and so on and I don't in principle yes but as you also put pressure on water actually the density of the water will go up as well and you might eventually be able to I don't know exactly what temperature but there is a certain temperature the lowest possible temperature you can reach as you put pressure on before it crystallizes so yes I would imagine that you could do that that you could actually slow things down but whatever the pressure itself will actually cause some other disturbance in the system it's an interesting point because another strange thing with water is that if you have eyes yes below the freezing point and if you think that you have a solid and you apply pressure to a solid you would think that you would so define it even more right so of course water doesn't do that as you yeah there you have it you could go to i3 but if you have eyes yes below the freezing point as you pressurize eyes it melts to work actually that's why we can ice-skate because as you go on the eyes you put pressure as if ice skates and you get a very thin layer of water yes so a green temperature do you think that the high surface tension that exists in water because of the simultaneous existence of the ice like structures and gas like so what is your question if he's asking anyway a little bit of a complicated question so maybe maybe yes summarize that further for the high surface tension guess it's temperature and water it's asking in a way if if you if you look at the high surface tension of water and whatever actually the boiling point is in between what you would expect for the gas and ice I think that's your question but maybe let me refine this a little bit the high surface tension I showed you a little bit now or the water structures in the ballot where we have these two these two different types of structures we actually don't know yet how this looks at the surface and my guess is that at the surface we might actually have more of this ice like and that's part of its try to form more hydrogen bonds and that's why you generate a high surface tension let's take another question here and I know that there are many yes so so I forgot so Rudolf Steiner is someone who I think maybe 50 100 years ago I was active to try to do something with water by actually and putting it into some sort of swirling fashion into the water and in that way make more water more having more special property and he mentioned here that we might generate more ice like configurations maybe I should make a real neural statement that that water has caused a lot of people thinking about many exotic topics like what you have said and many other topics and from a scientific point of view and I only speak as a scientist there is no way for us today to see any of these speculations of uniqueness of water base of any of such a treatment we don't have any experimental evidence that actually something is is happening with the water when we do any of that however having said that we cannot say either that is not true if they are simply we don't know yes maybe ask this question the right way when you chart the two peaks in the spectrum yes liquid water any also I indicated at 4 degrees water's most dense to those spectrum intensities shift as you might yes they do so actually let's see if I can go back to that might might be a little bit let's see if I can do that I can just show quickly since this might be a little bit of a detailed question for someone interested in the details but so here we see these two peaks but actually what happens is interesting as you change the temperature if you cool it down I said that we will get more of this ice like so what happens is that this structure this intensity grows and this goes down so you see the conversion of the disordered structure into this ice like structure but that doesn't happen to peak at 4 degrees now because the 4 degrees has the balance of those structure to contract and then converting between them so it's the balance of that that makes the maximum at 4 degree so I can also us mentioned for someone whose interests I talked about this disordered structure that is getting with increasing temperature more and more excited and more and more disordered and what you see as you increase the temperature that these actually shifts more towards the gas phase as you go up yes yeah so he's asking if the ice let me go back to this picture so I could oh sorry I'm going wrong directions so we couldn't see what we are talking about is gas 'king if these type of structures press a dice like structure if they will actually become large or as we change to actually lower the temperature and the answer is yes we see in the in let's say what we call ambient water which is the temperature water here in the room around that temperature they grow a little bit larger but not very much however water can be supercooled why we mean that we can cool it well below freezing and there we expect these to be actually starting to grow very much larger much faster than what you see at room temperature so we would expect them to grow larger but under these conditions not much has changed in size and those people who would like to do we still have cookies and said that I can't see the yes let's go thank you

Channel: SLAC National Accelerator Laboratory

Views: 63,630

Rating: 4.7701149 out of 5

Keywords: physics, Department of Energy, DOE, Stanford University, science, science lecture, science talk, public lecture, SLAC, linac, accelerator, photon science, X-rays, light source, synchrotron, SSRL, x-ray diffraction, environment, renewable energy, water, science video, physics video

Id: 7hGqlEpvODw

Length: 74min 54sec (4494 seconds)

Published: Wed Feb 09 2011