 Ladies and gentlemen, it's a pleasure to introduce Dr. Gregory Hogstead, who will introduce Professor Dijen. Dr. Hogstead is a 1985 graduate of Gustavus Adolphus College, who then left us and went on to earn his Ph.D. at the University of Minnesota and is currently employed there as a research associate at the Center for Interfacial Engineering. Today's final speaker, Pierre-Gilles Dijen, is a theoretical physicist with an uncommon ability to extract underlying fundamental principles of nature from complex systems. His four decades of work seem to span the entire spectrum of condensed matter research. Magnetism, superconductivity, liquid crystals, synthetic and biological polymers, gels, surfactants, wetting, adhesion, viscoelasticity, fracture, an unparalleled display of versatility and creativity. His theories provide cornerstone understandings of several broad and largely disjoint fields, as witnessed by the status of classic achieved by three of his books. These works have had a vital impact on research in physics, chemistry, material science and engineering, and technologies ranging from plastics to flat screen video displays. In the 1980s, Professor Dijen became interested in interfacial problems, that is, the molecular structures, properties and interactions localized at the boundaries between dissimilar materials. His writings provide unified and elegant descriptions of the spreading of liquids on surfaces and behavior of polymer molecules attached to surfaces. He has succeeded in combining the rigorous and mathematical with the intuitive and visual to shed light on the physics of interacting chain like molecules. These interactions lie at the heart of the science of soft matter, a term Professor Dijen applies to materials displaying both complexity and flexibility. Of extreme technological importance are the scientific principles governing adhesion at the molecular scale. This is the subject of Professor Dijen's talk today. Professor Dijen. First, thank you all for coming in this dark room rather than staying in the sunny gardens. I will try to talk only about simple things and about glues. That is a very good starting point. From long ago, from the Stone Age, we have been able to operate glues. I have listed a few spectacular examples here. One which has had a strong historical impact is the Phoenician invention of materials who were both glues and sealants, and which then could allow to build ships which resisted all the torments of sea. And the success of the Phoenician Navy apparently is largely due to this particular invention, so that a simple modest technique like this has had a large impact on history. There are many examples of this sort. I won't go in all these examples. Let me go on with the more recent part of the list. In the 1900s, we began to be able to bind shoes with suitable glues and wood. And something very important happens about this time. Two things converge. Science often proceeds by the convergence of very different abilities. In this case, on one side we have the invention of artificial polymers, long-chain molecules. These things begin to be created at the early times of this century. And the second converging factor is the onset of the aircraft industry. These early aircraft are built of wood, and very often it is needed to have them glued. The convergence of these factors creates an amazing chemical revolution. We were talking about the inventivity of chemists. They have been just amazing during the following years in creating new systems, which we now practice in every day of our lives. And for instance, we can say that we can glue together things which in my youth would never accept to be glued, such as metal and glass. So we also are in a situation where we can glue things and have them stay together even at very high temperatures. For instance, in the nose of a plane or a missile where we reach temperatures which are the ground of 400 centigrade, we can operate, build up a thing with glue to resist these high temperatures, at least for the lifetime of the missile. Similarly, we can glue things very fast. The typical process is when you bind books or something like this. This is done by a very clever group of agents called the hot melt which are able to stamp and get cold very fast and get your book being bound in an extremely high speed. So this is a great art, but it is a difficult science, as most novel sciences. Being a teacher, I had to try and teach courses on adhesion and principles of glue and these courses are extremely painful at the start because they really look like cookbook recipes. Cookbook recipes are quite useful. Very fortunately, we can use it for, I don't know, New York steak in this country or corn, things like this. Cookbook recipes are dangerous in technology because if a new problem shows up, it is not at all clear that you can solve it with the old recipe. And in this sense, you need deeper principles, which are just in birth. We are not yet very far in this. The difficulty is quite clear. This thing is mixing chemistry. As I said, chemistry is so inventive in this. Reology, the way things deform and flow and so on. Fracture mechanics because ultimately you separate two parts. You create a fracture. Surface physics because you are operating on surfaces all the time. Maybe the most unifying feature is polymer science. It's the science of long flexible molecules. If you wish of noodles at a minute scale. Polymers are omnipresent in this thing. All glues are based on polymers. And we may come back to this in a few instances. There is another part which occurs in these young sciences which is that you often don't really know what you should measure. You see, if you think of defining the quality of the glue, the natural thing you do and which is done by engineers for 100 years or so, is you take two solid pieces and you paste them with some glue and certain area A and then you let the thing incubate. Ultimately you pull with some large force F and you look at what particular value of the force the thing ultimately separates. And you have a sneaking suspicion that it is not really the force that matters, but the ratio of force to area, what we call the stress. So you're tempted to say that this critical stress, sigma C is the thing which defines the quality of an adhesive. But not so. And to show this to you, let me start by another type of experiment which is again something most of us have done once or twice. Suppose you have a piece of scotch tape, this is the scotch tape, and you've stuck it on a vertical wall. And now you start peeling it in a certain direction with a certain angle here at a certain velocity. This is written in French, I apologize, but I think it's a good exercise for you to guess that this means peeling. But what you measure in this way is the force per unit length along the third direction here. The force which is required to pull out your scotch tape. This has dimensions of force per unit length or energy per unit area. And it is the crucial parameter describing how a glue works. Let's call it G or separation energy. It is in fact more than a parameter because you can repeat this experiment at various speeds and you will get different numbers. You will have a whole plot of separation energy versus velocity. And this plot tells you a lot of things. For instance, if you are interested in having adhesives for this thing on the ground here or adhesives for these things on the wall, you're not at all using the same parts of this G of the function. This thing really works at zero velocity. This thing is related to what my heel does on the surface and operates at finite velocity. So this whole function here contains a wealth of information about the quality of glue. But the puzzle is the following. This animal, this separation energy, has nothing to do with the separation stress. In fact, they don't have even the same dimensions. This G is an energy per unit area while a stress is a force per unit area. So we're talking about two completely different objects in science and how do we relate them? Well, this was achieved in the 20s and 30s by great people in mechanics, in particular Griffiths and a few others. And it's an interesting point. Here I have shown these two solid pieces connected by a certain thickness of glue. I've called this thickness W, typically something like a fraction of a millimeter or less. And I'm pulling hard that at some moments the glue breaks. I've shown this here. There is a fracture which is expanding towards the center. Now what is the condition for this thing to happen? The answer which Griffiths provided is about this, that in this region here, which is not fractured yet, the poor glue is suffering very much. It is distorted by the stress and it has stored elastic energy. And the moment this thing decides to break in is the moment where I can transform from this deformed glue to relaxed glue in the fractured part in such a way that the elastic energy stored here per unit area just balances the G energy, the separation energy. Now this defines a certain relation between the stress and the G. But look at this. The elastic energy which is stored here depends not only on the stress, it depends on what thickness I have. If I have a large thickness, I always will have a large energy stored. And then a very small stress will be enough to provide this balance. The conclusion from all this is that the stress, which we measure when we separate two pieces, is not an intrinsic property of the glue. It depends on how much thickness I have chosen to put. Sigma C is not a well-defined property of a glue. The sad thing is that all the engineering tests operate in the opposite order and measure sigma C. But for all fundamental purposes it is the energy which is the important thing. But so much for this definition of adhesion which was provided to us by the people and mechanics. Let me go to what makes things stick. And as often in theory, and in fact as you may have even noticed in the talks today, theorists operate in the following way. They have a problem and they say, oh, I cannot solve this problem, but I can solve another one which vaguely resembles the first. But this is exactly what I'm going to do for a start here. In one case where adhesion is relatively simple to understand, it is when I have a very poor glue. Let me take a simple example. Here are my two hands relatively clean. And let me put them together. There is some adhesion between them. There are what we call in chemistry van der Waals forces. There are little attractions between the molecules or proteins at the surface of my hand. The forces are quite weak and the net result is that fortunately I can separate my hands. What is more is that when I do separate them, I find them approximately in the same state they were in before, which in our pompous language is called a reversible process or a thermodynamic process. Now the meaning of all this is that in this weak limit we can describe adhesion if we know the energies involved on the surfaces, the energy of this bare hand against air and the energy of these two hands facing each other, the surface energy. If we know these, we can predict everything about pulling out, pulling in, because we know the corresponding Gs. Let me show this to you first on a simple example. Suppose I have pasted this glue in liquid form on my surface and I want to paste it well. Now to paste it well, the situation must be such that really the solid surface likes the glue or any more physical term if I compare the surface energy of the bare solid to the sum of solid to glue and glue to vacuum air. Well if I make this comparison, I must gain an energy by spreading. This is what is described by this coefficient here, which is called the spreading coefficient. If this coefficient is positive, the thing will like to spread and this is what I want. In fact this coefficient is an American invention, Cooper and Nuttel during First World War. They were concerned with spreading insecticides on leaves and they realized that the very insecticides worked well if this parameter here was loud. So you see very practical things lead to pretty universal concepts and all these things. Well this is experiment one. If I want to have a glue which spreads nicely, I want this combination to be positive and this is useful because very often I will have a poor brush of a surface will be a regular fix of the salt and I want this liquid spontaneously to go in all the little corners. So I want this. Then second experiment I have prepared my glue and it has in some sense dried out or cured so it has become somewhat solid. Now I break it because I have two pieces again and I separate. Now this breaking may happen in two ways which I have shown here. One way is in the bulk of the glue, what is called cohesive rupture and clearly the energy to create this is just two times the surface energy of the glue or there is another possibility which is that the glue really had no very strong affinity to the solid walls so that then I will detach at the solid surface and then the energy involved in creating this thing is the difference between this pair and this thing here that's this combination here. Now you see I have two possible ways of breaking my glue and they cost different energy. In most cases what nature will choose is the path of least energy just like we do and the net conclusion is that I have to compare these two if I take this difference G adhesive minus G cohesive and if this difference is positive well I'm happy, I'll tell you why because if it's positive it means that this will occur and not that and this means that I will not be dependent of having not really stuck my glue properly to the wall I will have stuck well to the wall and I am limited only by the intrinsic strength of the glue this glue has to yield at some moment so I want this rather than that it's an indication that I work properly. Now if you look at the simple algebra which is involved in there you end up with a remarkable relation which is one of the few happy surprises of nature I would call it which is that indeed if this Cooper natural parameter S was positive which is what I want for spreading well at the same time this energy difference will be positive which means that I will have the cohesive rupture which I want but why did I go into this exercise it is to show you the sort of arguments which we need when we build up things starting from these energy ideas we measure these energies by various tricks and then we can predict the quality of this or that system provided we are in the weak adhesion regime this is not useless the first example is these post-it papers which are sold by 3M and made not very far from here in fact another example I met after a talk like this I was going out and the young man comes to me and he has a photograph in his hand and he says you know I think you might help me I make sculptures and he showed me a beautiful sculpture of his girlfriend a bronze which he had made and he had the photograph indeed no problem with a girlfriend but he said I have a problem and that was the following putting a mold directly on her body and in some instances it worked and he could take the mold out and cast the bronze inside in some cases the mold didn't want to go out and then his relation was in great danger so he wanted help the answer is in fact provided by chemistry nowadays when you mold statues in the mold in this plaster you put a thin film of silicone oil and you ask this film different requirements it's a more complex problem than this one you ask it to stick to the plaster and to quit the bronze easily once you have formed the bronze but to stay on the plaster side because you want to use your silicone layering many times so you see this is a more complex problem because you have the girlfriend and the silicone and the plaster and the bronze there are more partners but you can discuss all these partners in terms of these concepts and come up with a safe operation for a couple like this so it is sometimes useful so to summarize this piece I would say that we have these weakly adhesive systems which are controlled by the weak forces which are between my hands and which are reversible and if you want to put a number into this if you do science you have to put numbers at some moment the energy which is involved the G's the energy per unit area is very small for our standard it is something like 5 centi joules per meter square so now this is not at all what we have when we buy a glue at the supermarket a super glue at the supermarket and we are talking about energies which are something like 100,000 times bigger than that so what makes the quality of real glue? well this is not entirely obvious and I have had interesting talks with my chemical friends about that chemists often think that it is very simple if I want to glue this piece to this piece I create some strong chemical bonds between the two and there is clearly some truth into this because if I do not create chemical bonds I come back to this hand problem I just have banned advanced forces but the point is that chemical bonds are not at all sufficient and this you can see just by numbers if you think of establishing chemical bonds between two surfaces and you count how many atoms you have per centimeter squared and you say that each atom has a typical chemical binding energy to its neighbor on the other side and you say I slice all that how much energy do I have to pay? well the answer is of the order of 1 joule per meter squared so it is 20 or 50 times bigger than advanced but it is still stupidly small when compared to realistic glue so we are still missing something very important and my chemical friends they don't always understand that I was talking not long ago with Jean-Marie Laine who is my colleague in France and who is a Nobel Prize winner in chemistry so he should know some and he had established a very clever system and he is a brilliant guy he had established a clever system where he could prepare two papers and one would carry a certain molecule and the other would carry a different molecule but these two molecules would recognize each other and stick while if you would use a third molecule on this side, no sticking at all so that was a very intelligent idea but I had to explain to him that if he created good bonds between the two he wouldn't have something sticky however he would have this very stupid number and not more I make him back to this point later because it's a nice point well what happens in practice if you break a glue or if you break a piece of plastic for instance a polymer substance is that you are very far from reversible conditions you are really hurting the material very much one example which I could take unfortunately I didn't think of bringing this but I could have brought a plastic bottle a polystyrene bottle this does exist still in the American market and I suppose I bend it very strongly but at the low place where I bend it very strongly I put it under strong torture you notice it becomes whitish this is something which you can really do with your kids at home becomes whitish that means that some objects of size comparable to the wavelength of light in micrometer or so have been structured inside this plastic sheet what are these objects they are what we call crazes beautiful word and beautiful object here is one craze in a polystyrene matrix all over there we have glassy polystyrene just as we know it it's a solid, it's pretty firm it's made of long molecules if you wish you could think of it as a plate of noodles which has been frozen something like this but I've been pulling on that firmly and this thing has partly yielded some bubbles of air have grown in this region in this very flat pancake region and the admirable thing is that there remains some connecting pillars if you wish like in the Greek temple but if I compare the sizes I am in the tenth of a ninth ranch something like this this is a very small Greek temple why do I have these pillars of matter well the answer is close to something you notice if you put your finger in honey or maybe maple syrup in this one you pull it out and you get a fiber and any viscous polymer tends to do this so that when I'm pulling here I'm pulling so hard that locally this thing is becoming a liquid like honey you're so tortured and this liquid makes fibers these fibers are very amazing their width is very small maybe ten times the size of a little molecule their height is much larger they are real pillars their height is in the ground of micrometers and this is why this thing becomes whitish and they still carry load you see this thing is not purely passive it is still resisting my force here this is why plastics are good incidentally it is admirable that they can resist much better than glass the reason why is this because these fibers occur when you have noodle-like molecules in it they don't occur if you have plain glass well this is the basic way which plastics of this family can make good glue if I ultimately fracture if I tell them I really want to separate you too I succeed in building a fractured region here but it is always announced by a long-case region and the energy which is dissipated in making these fibers from a glassy material is very large for that reason we have very robust plastics and very good plastic glues this is really one of the major sources of polymers as adhesive the fact that they can make these very dissipative structures it's not the only process and I cannot resist talking to you about another example because it has a connotation of everyday life you have all watched car races and you have seen these cars changing their tires very often every second hour or so and you may have noticed that when the pilot has changed his tires and he is leaving out his screeches and so on he leaves a very dark track under each wheel this rubber which he has on his tires is so soft that it leaves a visible track all along it's very soft rubber or what we call poorly cross-leaning rubber why is this a good thing? well let me spend a minute talking to you first about what rubber is here is the basic experiment about rubber which has been performed by American Indians for 4000 years or more they take the sap, the latex from the heavier tree some sort of whitish liquid very much like what you find in the dandelion here and they paste it around their foot and they let this thing so-called dry for 20 minutes or so lower and behold after 20 minutes instead of remaining as a liquid it was a liquid flowing like that what they have is a boot this amazed the early explorers the 18th century explorers they were very surprised by this and it became a very powerful technology something like 1840 or so when Mr. Goodyear changed the procedure slightly and produced what we call now natural rubber what happens in this process? well the description is about what I have here the original sap is something of this sort it's like noodles floating in broth you have independent noodles and they manage to worm their way around each other in some process so it flows, it is a liquid but then oxygen from the air comes around and reaches this structure and oxygen has an admirable action it binds noodles together so that if you started from this you end up with something which looks like a network where the chains are connected now locally if I am a very little fish much smaller than this I am swimming, I see no big difference between this and that both are liquids locally but on larger scales if I pull on this thing this is not a liquid because it can resist deformation stuff so this is a very special type of soft solid and this is what we call a rubber so this is what happens in the boot of this gently incidentally it's not a very good boot it breaks after a day or so because oxygen does not stop at doing this useful purpose oxygen also has an evil action and it decides to nibble the chains themselves it cuts them into pieces and if you take a network or a fisherman's net something of this sort and you cut it in random some critical moment it collapses that happens to the boot here and this is why oxygen is not the best system and Mr. Goodyear by pure luck apparently had the idea of substituting sulfur for oxygen boiling this sap with sulfur and obtained a beautiful rubber which is our natural rubber why is that? it is because sulfur does bind the chains together but sulfur being less reactive than oxygen is not strong enough to do the clipping to do the evil action and for that reason sulfur is still used nowadays to prepare rubber so this is what rubber looks like now I have to explain why very soft rubbers are very good for racing well a very soft rubber or as we call it a weakly cross linked rubber is something where you have very few attachment points so that many chains would be stuck at one point and will be like a long dangling arm now this has very special effects because if I now deform my rubber God knows that in these races this rubber gets very strongly deformed if I deform it these chains take a long time to adjust to the comparison which is due to my colleague Michael Rubinstein which I like this long arm here, this long flexible arm is reminiscent of an octopus being trapped in a fisherman's net and this octopus tries to get his arms back and forth and so it's very painful and very slow so conclusion these weakly cross linked rubbers these weak rubbers have very long relaxation times slowly when they are told to do something why is this good? well I'll try to explain it in the next little drawing this represents a tire you should think of a wheel of a car something pretty large here and we're just watching the bottom of a wheel and it is sticking to the road for a moment I'm talking about a dry road and it is sticking here and this car is advancing at a velocity this is not a race car really which I had in mind here 60 kilometers per hour now you people don't know what a kilometer is a kilometer is a unit which is still used in some savage countries beyond the ocean but this means 40 miles per hour something of this sort well what happens when this thing is moving forward this part is stuck it doesn't move for a moment what happens is that this piece is separating air is entering on this side and this front of the fracture if you wish is moving at 40 miles per hour in this way so in this region all horrible things happen the rubber which is sticking directly to the road is torn out and suffers and moans sometimes audibly but this is not the whole story apart from that something else happens because you remember this rubber is a very slow operator it takes it a long time to understand that it has been suffering so when this thing moves this piece of rubber one particular piece of rubber goes here and is torn but it begins to relax only much later when it is in this region in fact at the distance VTOL where V is our car velocity VTOL is the relaxation time of this rubber typically VTOL will be a millisecond this velocity is 40 miles per hour and so this distance is a centimeter or so so what I am telling you is that in this system not only do we have horrible sufferings here which give a big adhesion energy that is always present but we have other sufferings widespread in this region and they will also contribute to the adhesion and this is why these race cars stick so well to the ground now those of you who are familiar with that sort of thing will say ha ha this looks fishy because indeed there is something occurring here but the stresses in this region are pretty weak the stresses were much stronger over there true the stresses are pretty weak in my red region here but on the other hand the size of my red region is huge something like an orange peel all around here it is very big and this overcompensate the net conclusion is that these far field losses as they are called in this region here can be a hundred times what you have in the near field region so you stick a hundred times better and this is how race car operates now as always in life there is a compromise in this because what I am telling you is that if I make a very poorly cross linked rubber a very poor network it sticks well but of course it is very fragile and this is why these pilots have to change their tires every second hour so you see I hope in examples like this that we begin to have unifying concepts we begin to have a few pilot ideas which allow us to teach to the students things beyond cookbook recipes now this is of course a very partial story and I cannot resist extending it a little bit because I have been talking about interfaces and I am tempted to show you another of these interfacial problems because here I can probably produce an experiment being in the United States I have of course chosen a very complicated setup it is based on this glass of water here I have a sheet of polyethylene polyethylene hates water it is the opposite of the Cooper natal liquids which liked the leaf here if I put a droplet you see it does not spread at all polyethylene hates it if I put more I can get a somewhat larger area just because of the reasons of weight because the weight of this thing crushes it out down to a millimeter or so but still the polyethylene defends itself and does not like to be wet now suppose I am more brutal with it and I do the following I spread now you notice that the polyethylene defends itself and that dry regions grow ideally they would grow like circles but they grow with random shapes because I am so messy here but if you have a sharp eye I think you will notice that the growth of these dry regions essentially proceeds at constant speed but to the moment where the thing stops because there is no water left this is what we call de-wetting and I have idealized it here by this little drawing and it is a subject which we have tried to study something like six, seven years ago looks simple but of course this is very messy if you want to do it cleanly you have to produce a very ideal surface much better than this current surface actually what I say to my students is this is very similar to the problem you have at home if your floor has got messy what does the family do? you buy a carpet same thing here if your surface is not very good what you do is you bind little molecules on the surface and you make a very dense carpet of these molecules and the language of chemistry which is typically done what is called silanation reaction involving a silicon atom and chlorine and you couple that to an OH group on the surface and it looks nice and simple but it is extremely delicate and sensitive to impurities to water and so on I like to quote this story because I think it defines a certain spirit and it's a spirit we should defend with our students we asked a young man by the name of Jean Bruneau to do this silanation operation and many French students if they had been asked at that moment to do this would have said oh this requires very pure conditions you must buy for me what is called a clean room some word like this in English this special room with no dust where you enter with a mask and so on and special costume a costary clean room at least $50,000 or so but fortunately for us Jean Bruneau was not of this type Jean Bruneau had worked in very difficult conditions with no family and in fact he was starting his PhD but gaining his grub by working at the meteorology station and during the night he would establish these maps which we watch on paper the next morning and then he would come to the lab at 10 or 11 in pretty poor condition but a strong person, very energetic person and Jean Bruneau did not ask for a clean room he fought for about a month and then he came back to his director and he said you know I will do this experiment and I think I can succeed but I will not do it in your messy lab maybe he didn't use these terms but something equivalent he said I will do this experiment one sunny morning in the park in winter which meant really in the low conditions of lowest humidity and he did that and just that and with this he got for what was at the time the best carpets available on the international market I think this example is worth quoting because in our days we often speak to our students of the very heavy systems of research that we have, the big machines the synchrotrons, the neutron reactors which we use all the time which are sometimes useful, no problem but they tend to think only of these and to forget this spirit of finding simple answers to a question before going to a big machine I think that's very important both from a point of view of a taxpayer who really does not always need the big machines and also from the point of view of industry because in industry in most cases when you have a sudden question about the surface problem like this say you're making photographic film and something goes wrong in the process and you don't have too much time you will not have the time to bring your equipment and your complicated setup to a nuclear reactor or something like this you have to invent simple means on the spot so this is a little parenthesis about education but in any case these people were able to find out the laws for this and to understand the relative processes which matter in this and incidentally we've been talking a lot about theory in physics today and material I think this might convey to you a slightly distorted view it is clear that theory is sometimes helpful sometimes completely wrong and Phil gave us examples of that theory can even have a very negative impact on research at some moment but for this sort of problem here I think the ratio is interesting you see these laws of de-wetting which I sketched here they were established by a team of maybe four experimentalists working for three years and six months two theories that's the ratio we need theory but we need a well balanced ratio and very often we suffer especially in our latin countries where the education is all based on theory we suffer from an excessive theory well let me go on since I was in this interface business and also I mentioned cars let me show you that this piece of work on de-wetting how this surface resisted being covered by water has found unexpected applications for us one is this experiment here this is a British experiment because it rains heavily and you can immediately notice the car is British so you have a film of water on the ground and you are again driving at say 40 miles per hour or so and you have a real problem there because a typical piece of rubber in your tire stays in contact in this immobile position stays in contact with this region here only for five milliseconds at this speed it's not very much and during this time you desperately want that the water film which I marked in red here goes out because if it does not you have lost your grip on the ground and you go in the next stage so we are facing a problem which is very related to what I was doing in my little experiment we have water which is against rubber and rubber doesn't like water and against asphalt and asphalt doesn't like water so this is favorable dry patches tend to grow but on the other hand we have a more serious problem than what I had because in my experiment the top surface was air and air is very deformable while in this experiment the top surface is rubber I like to be deformed by that so for this reason the laws of growth of this thing which are sketched here are very different and more sluggish than the laws of growth for the experiment I had before now this in some sense has helped to understand this process which I think in English you call hydroplaning in French we call it aquaplaning will it have an impact on the car industry I think not the reason is that people who make tires have tried everything and they have come up with the best answers which are compatible with other constraints and for instance you could think of drawing some very fine little ditches on your tire and you would improve the evacuation of this water but these little pieces would be destroyed by driving one or two days so from the point of view of the car industry I don't think that these studies will bring a lot on the other hand they may bring a lot for the road industry because roads are made from a collection of little stone particles covered with asphalt and an intelligent choice of the distribution of sizes of these stones will react on this process in a useful way so the hope is that these very fundamental ideas about de-wetting will find out will find some industrial channel in this case this was the first example which came out of this little experiment the second example is very different it is related to these stupid magazines which we read every week these splendid four color magazines they are very stupid but they really technically are very beautiful when you look at the quality of the images and when you look at the speed these magazines are typically produced by what is called the four color offset system they are produced at 35,000 copies per hour printing four colors that's where our worries are and sometimes for instance in a blue sky, you want a blue sky and what you see is a cluster of white spots and the French printers call that moutonage a mouton is a sheep it's like having an assembly of sheep in your blue sky and it's no go and there was two years ago there was a real question about this moutonage how does it operate but the answer is that it is again a little cousin of my experiment here because when you have printed say the green color you wanted to print some other parts in blue so you have protected the future blue parts by water, by a water film and then you bring the thing after it has been printed in green and other spots in front of this roll which will put in the blue ink and all this is proceeding at these very high speeds 35,000 copies per hour so again you must dispose of a water film in a very short time and this resembles a proceeding experiment it resembles but it's not identical because here we have a relatively hard partner which is this roller and on the other side we have the paper our magazine's paper and this paper sucks in the water so it's a different family of dynamics but if you play with the same concepts and same family of experiments you can come up with some I would say some rules of the firm about how you can fight this moutonage and apparently this makes the printers very happy well this was let's say industrial contact number two in this little sector let me end up with this last one which I like very much which is from just a year ago the fall a time where you work in vignette a typical problem with grapes do you grow grapes here I'm not sure in Minnesota but you have heard about grapes I mean I've seen grapes being grown in New York state with very little success as regards to the wine but they do grow grapes but a typical problem is to protect these grapes from various fungi and the way you do this is you send some sort of mist which I have tried to represent here by these little red droplets and this mist will surround the grain and hopefully it will do this it will create a uniform film of something which is mainly water you cannot use any other liquid than water for health reasons nowadays so this is mainly water plus a little fungicide inside and hopefully it will surround the grain and then if it dries out you will have an interesting protection but unfortunately a grain is covered by what people in agriculture call waxes and waxes are very much like my polyethylene sheets these waxes hate water so the net result is that the surface of the grain does exactly the same thing which I was showing to you with my little experiment it grows dry patches like this and these dry patches push out the water and ultimately the water collects in the form of a little droplet at the bottom of the grain and this is disastrous because typically this grain is a centimeter maybe California is 2 centimeters this thing is a millimeter in size so in linear dimensions you lose a factor of 10 in areas and treated areas you lose a factor of 100 so what can you do? well this is a problem we had a good cooperation with an industry which is Ron Poulenc Ron Poulenc having a lot of interest in agricultural products and starting with the same concepts and the same family of experiments Ron Poulenc people were able just a little more than a year ago to produce an additive which when put into this thing will prevent the formation of dry patches although in equilibrium we would like to be there but this thing blocks the motion and the net result is that maybe we don't gain the factor of 100 which I estimated here but apparently we need something that like 10 times less fungicide than we needed before so you see this type of research can really help in our everyday life and this brings me back to something which Phil said this morning the science of everyday life is very important it is important for many reasons it's important because it's urgent for us in many cases but it's also important because it has been underestimated because all the preceding generation was so excited with the great discoveries of big things like galaxies small things like particles but everyday life at that time was not considered in fact all what I have talked to you about if it had been presented say five years ago would have been considered as a very messy strange subject not worth of being talked at in equilibrium but now things are different and the science of everyday life is coming slowly up and hopefully it will help each of us it's important from that standpoint it's important also from a tax payer's standpoint it's also important for us teachers because of our students I find that in many sectors of science the directors of PhDs and so on have a very reckless attitude where they put students on subjects which are of interest to themselves but not necessarily of great national interest I think this is not acceptable anymore it was in the very expanding society of the sixties and so on but it is not anymore and we have to be very careful on that and this is the reason why this sort of simple experiment has a reasonable future but I'll stop at this point and thank you very much for your patient attention the ushers are circulating now with cards for questions let me remind you that this evening there will be two Nobel firing lines one of which will be involved with three speakers from today and the other will involve the four speakers tomorrow if you wish to hold your questions some of your questions on today's talks until this evening you're welcome to do that those firing lines start at 8.30 and they'll be held in the canteen and an alumni hall I believe the one in the canteen will be the speakers from today and the one in the alumni hall will be the speakers for tomorrow also since some of you will be leaving I want to point out that this evening we have a concert in the chapel at 7 o'clock that we have a wonderful display in the Schaefer Art Gallery you're all invited to see that and then once again the firing lines will be this evening we have an opening question I well you've gotten my interest suspected you mentioned my friend Jean-Marie Lane and his recognition molecules which many of them actually involve the kind of bonding that you didn't talk about you talked about putting your hand together and that comes apart because the most you can have there is probably a weak van der Waals interaction you talked about the really good glues which have crosslinking and a lot of covalent interaction but you didn't talk about hydrogen bond interactions and if your hands in fact were orchestrated in such a way that you could form many hydrogen bonds it might be interesting it might be very sticky several questions one are there glues based on many many hydrogen bond interactions two what's the mechanism of breakdown of a glue at high temperature is it is it just cleavage of bonds or is it once again the evil action of oxygen or is it both and finally if the bonds don't add up over a certain surface area to give you the adhesive energies you're talking about what is the answer let's take three questions in order hydrogen bonds in action you quoted this example of nucleotides now we have an example in everyday life I would say which is when we face a siloxane chain silicone oil against things like silica usually you'd think these two things don't care about each other but in fact if you let incubate silica in front of silicone oil for something like hours or so at room temperature you end up with a sticky surface and apparently some bonding has taken place or some poison has been eliminated you're not quite clear but the possibility of hydrogen bonding between OH groups of the silica and the siloxane itself the oxygen from the siloxane is a good one hydrogen bonds we do meet now let's take question number two was the breakdown at high temperature what is the mechanism of breakdown so we have cases where oxygen is the promoter of our glue because very often you have a glue which is a flask of salt and it's protected from oxygen and oxygen will act to induce reactions a little bit like in the Indian experiment but in a more sophisticated way I should say inversely that there has been beautiful inventions going the other way the so-called anaerobic glues which operate in such a way that they do not stick in the presence of oxygen but if you put them in between two metals like copper then the atmosphere which the copper created is a reducing atmosphere will induce a reaction so this thing will stick only and it is exposed to the right metal and this I think is beautiful chemical invention so there are but if you ask me about mechanism I find that even in this anaerobic process which is a beautiful invention ultimately we know a lot about chemical kinetics in it but we don't have a complete vision of how it works so my general feeling is that most of the degradation studies still need a lot more and the third one is about so what is the energy component in this crazy case it was pulling out fibers in the race car example it was this slow relaxation very far from the object in Jean Marie's case the answer is that if you just put the two molecules stuck on two surfaces you won't get much but if you put them on two spaces you chemists are very good at providing intelligent spaces then the spaces will store elastic energy and when you separate you will have much more energy to sacrifice so the trick to make Jean Marie's object really useful is to put it on long spaces I'd like to ask Professor Pichin and also the panel who reflect a little bit on mathematics we philosophers sometimes look over at the scientists and develop the case of equation empathy something that we really tend to be bereft of by and large although some of the logical folks try to develop symbolism with rather extensive character but still it's not quite the same as mathematics in science and I'm curious that wonderfully lucid talk that Professor Pichin just gave in the middle of it said to do science you must put in numbers at some point and of course we all recognize that that is true at the same time the talk that you gave was so lucid because in fact there was not very much in the way of appeal to our sense of the intuition of the relationship among variables and it set me thinking as to what the real importance of mathematics and some of its dangers might be that is not obviously helps us in many ways it helps us in terms of precision its precision helps us in terms of prediction there are certain definite human purposes that mathematics assists but on the other hand it's highly abstract and it is in fact so abstract that unless we already have some prior concept of why it's important we would have no good reason to be interested in a scientific way we might be interested in mathematical pure way but from a scientific point of view we don't know why we should be interested in a set of mathematics unless there is already something there to guide our interest and furthermore mathematics could even be so precise and so compelling that it might make us think prematurely that we have entered the domain of the boring and because it is settled in mathematics when in fact it is not settled although it's settled as a sociological fact it somehow comes unglued again make a bad upon on your point but so what I'm curious about is why mathematics I mean of course yes we need it but do we need to keep it in some kind of balance as you said yourself similar to the way in which theory is related to the practical aspect that I'd like people to give me a sense of sure we'll have many reactions to that why is that? first observation is that this sort of discussion is very different in our Latin countries and here young students are usually underdeveloped in mathematics and the dream of having been learning a little more in the French system it is different they are selected by mathematics by and large and this I find a very dangerous thing I'm very fond of mathematics I think all of us are fond of mathematics as a scientist but I'm not fond of it as a selecting agent because then it is all based on one particular ability which is beautiful ability but it is not the only one in life and qualities such as the sense of observation and the sense of a certain handicap which the Japanese have so much which we have sort of these senses are completely underestimated in our French selection system because it is entirely based on mathematics but from that point of view in France I'm very critical to the role of mathematics in education although I love that as a scientist the question is an interesting one people sitting at this table being a historian what I always found interesting is that in the physics and mathematics as the supreme model for how to resize pure area is trying to understand how chemists think because their language the kinds of symbols which they use are not mathematical and trying to understand precisely how they develop an intuition into their world by using a kind of imagery and a way of representing the object that you deal with is having explored Caltech where the only criterion we have for acceptance is mathematics I mean we look at mathematics scores and if they're high we take people if they're low we don't we don't have a way of really looking at what you're getting at here these other powers of observation staying power etc on the other hand without mathematics chemistry would be absolutely nowhere nowadays all of the modern advances in chemistry have come with based on mathematics an ability to actually do mathematics in one way or another and that's what's lifted chemistry out of a sort of dark age into a real revolution that in a lot of instrumentation a lot of high powered instrumentation the ability to work with it so I think the chemists would be horrified actually to think about now working on it to the future without building in very deep mathematical roots and so forth although we are a little crazy in giving talks we tend to give them without mathematics to try to communicate there is such a thing as a language of chemistry it's based on the periodic table you can chemists go around on blackboards drawing little lines and so forth and communicating without mathematics and it's kind of weird to watch them go around they have this language and if you're into it then you're okay and if you're not then you may as well have mathematics but you can you can discuss chemistry and large parts of chemistry without mathematics if you learn this foreign language it's called the language which is based on the periodic table but these are just rambling observations if I might I think it's more than just foreign language it's really metaphorical we use models when we teach students about chemistry that are drawn from daily existence and these things just don't translate well to small objects and so I think we use mathematics to keep those models under control for a reality check on those models I think there is a little rather limited validity to your questioning of the use of mathematics I'm not sure that it's to be answered by the use of less sophisticated mathematics but to the by the use of more general concepts I mean mathematics is in fact crystallized logic but more general concepts of logic concepts using inequalities rather than equalities geometrical intuition you know there is no no really perfect way to express a fractal in mathematical terms yet you can describe the concept perfectly well so would you say chemists have actually figured out how to do this kind of mathematics for their kind of thing and if we could figure out exactly how they've done it that would be a new different kind of mathematics it's a kind of combinatoric perhaps I find in physics that people are much a physicist because they're mathematically they're in background as mathematics are much more enamored of an answer that gives them a perfect or a beautiful mathematical curve and they are of an answer that tells them well this is right and that's not right because there is this qualitative inequality this qualitative difference between two behaviors one with one temperature dependence and another with a different one which is not expressed really in mathematical terms someone else will come along with a computer curve and he says I can make something vaguely like that with my computer and the average physicist will believe the second man who is in fact not using as good mathematics well you all demonstrate today I mean Professor Dijon says well I can't solve the real problem but let me show you the one I can solve and it's pretty close to this one so let's talk about it and that's not bad Professor Dijon a question from the audience is it possible to make a solid with a surface that no adhesive could stick to if so how if not why not this is a very important practical question and I'm very proud to say that we French have a company who has provided the closest answer to this this is the so called Tefal frying pan what is it made of surface covering a steel frying pan Teflon is really one of the materials which has the weaker van der Waal's forces so it sticks less and you can cook in one of these Teflon and it will not stick this has been a beautiful story it started by two anglers who loved to fish trout and who were interested in frying pans and they decided to establish a small company in a location near Annecy where there is a lot of trout they started this company and it went very well for a few years at some moment they started selling frying pans in this country and then the DuPont company got mad because they were using Teflon and Teflon is a DuPont invention so they tried to destroy them just like Kodak they tried to destroy Polaroid or things like this and the fight was really David against Goliath Goliath has something like 100 lawyers on the case David had one lawyer but he dedicated group a small group of scientists and ultimately David won so I am very fond of that story another question from the audience does adhesion have any role in the function of detergents wait you might say that many detergents fight against adhesion that they will make it sure that a dirt particle will not stick to a textile fiber for instance so you might say that certain detergents are really lowering a certain G function it's not their only role I mean they are active also as solubilizers they are active also and when you dry things for instance after washing all this little experiment I didn't mention that side but this little experiment on de-wetting is also very important when you wash your glasses and so on because if you do not have this process which takes things away when you dry you would recover the little dust particles which you have strived to get out of the surface which just fall back again and then the trick is to operate this thing so you see detergents are important two or three stages in this washing operation with different functions one of them is very much what was said in the question there is a question I think I can translate a little bit it concerns the capabilities of metal matrix composites for bonding and their potential use and high strength low weight applications for example airframes metal matrix composites I would say probably the challenge of our day is to construct this aircraft which will fly from San Francisco to Hong Kong with non-stop and this aircraft cannot be made of metal it has to be made of a composite which might be carbon fiber against a very strong glue and Dupont has patented some remarkable glues to provide the matrix in this case now the interesting question is that it is not yet sure whether Boeing in this country will make this aircraft or not and I'm very worried admittedly it's a terribly difficult construction and you have to think of what it looks like typically you have I don't know the English words but you have this piece which stands high up in the air behind the plane it's about the size of this ceiling here and you're wrapping up something like huge bandages around the model of this thing and cooking then this up to 400 degrees centigrade and you should operate it in such conditions that it never distorts in any way that it's ideal so this construction is very hard and at the moment the people I'm told from Boeing and related companies are afraid of embarking in this program for the big parts, for the wings and so on and they use it already for small parts but for the big parts they are afraid and if they are afraid and if they don't do it it is very clear in my mind that the Japanese industry who is already a contractor of Boeing who is learning the Boeing tricks very fast within 5-10 years the Japanese industry will do it and because they are so good at this handicraft part they will have the technical staff to do this bandaging thing when I wonder if you'd be willing to share a couple of the areas that you believe in adhesion hold the remaining important questions to be answered well it's a sad statement but there are many things which we don't understand at all, for instance I mentioned these polymers which craze and for the crazing process thanks in particular to you Brown in California I think we understand the G function pretty well but if you take some of the glues in supermarkets precisely these so-called superglues based on epoxy polymerization well these things don't craze they are strongly cross linked so they cannot craze they cannot pull out in fibers and the exact process by which an epoxy glue dissipates energy I don't understand at all so I think that is the big challenge of the time because it is the typical question which your child will ask how does this superglue work although superglues are extremely glassy and that is that's a collection of questions I have I'd like to thank all of our participants and all of you in the audience for staying on with us once again let me invite you to the firing lines tonight at 830 in Alumni Hall and in the canteen area and have an enjoyable rest of the day thank you