There is a title for my presentation. I'm going to talk about the fabrication of super hydrophobic silly looks or faces. Why a plasma processing. I'm going to follow a pretty standard outline here. Were giving news some valid ground about super hydrophobic surveys and class process ones and then some experimental results from pollution and knowledge Ment's. First let's go through some basic definitions. When eighteen not five Dockery and forced explain the relationship between a liquid and a solid interface. From where we got the idea about the contact angle. He actually wrote an essay on this. And later Gibbs. Took that concept and he formulated that equation but does not call this deep secret in it still call this young see creation I don't know why. Based on this contact angle definition if if a surface has a water contact angle lesser than ninety degrees the surface can be termed as hydrophilic right. And if it is greater than ninety degrees it's hydrophobic. For the past twenty years there has been an increased interest in fabricating a super hydrophobic surface which has a contact angle greater than one fifty degrees these surfaces are of greater interest because when a water drop rolls off on the surface it can face the dust particles from the surface and if it leads to an eventual self cleaning mechanic from and that's the reason for the lotus leaf and other things like butterfly wings and seek out wings to how the self-cleaning McCann is a major US provided them with super high support races. This interesting concept was very much. Interesting to many researchers where they fight to mimic the surface. When they try to mimic the surface. What they created is they can create an extremely watery balance or face. A self-cleaning surface we can also. It selected for me able membranes and waterproof garments and what not. That is a first how we can engineer these super hydrophobic surface. If you have a low surface energy through chemistry the highest contact angle what you can get is one thing. Even if you sat with more and more foreign groups. You can get a contact angle greater than one three three through surface chemistry. Then how it is possible to get greater than one fifty degree the clue lies here. If you think about the air water really doesn't like air right that's why it slides out for it'll fall. So in principle we can assume that the contact angle made by the liquid with the air is one eighty degrees. And this surface explains that all if you are if you have any fork it's between the surface. What happens is you get to compensate for the contact angle. One is from the solid surface the state are why is the contact angle made by the liquid on a smooth surface those blocks are strong and the right side of the equation is for the air part. F. is actually the solid fraction so one minus if it's the air between the liquid and solid So you have these two confidence of equations. This one. You cannot get about one twenty degrees for the reasons I explained previously and this you can get one eighty degrees when you combine these two the parent contact and what you see here can be bumped up. So that's that's how people started getting contact angles greater than one hundred feet of nice. And it's interesting to see that. OK took to get this property that there are two two things the rule of thumb Oneness a low surface energy material that is for the first passed right and the next one is a roughness scale such as Micron and sub Micron scale what does does that doesn't. You. You have the air air focused between the liquid and solid interface. And if you see the image of a lotus leaf. This is what happens there. It has the least. Points. It has a low surface energy material at the same time it has a micron a nanoscale roughness which makes the water to stand like this on a lot of sleeve. Right so. This property for from from from the by creating these two properties. People started maybe making artificial super hydrophobic surfaces. There where there are inorganic substrates which are super hydrophobic But the problem with that is they are inflexible and not via visual when you think about organic substrates to make it a sobriety variable super hydrophobic surface they they are often expensive. So the search for a bio degradable renewable inexpensive biopolymers it's still going on when we thought about the choice of the substrate we thought about cellulose people now are working with nanotechnology So there's a new polymers but there is a polymer provided to us by the nature right. The cellulose the cellulose is bio degradable renewable inexpensive and of course it's a by polymer to be to be more specific if you think about the cellulose paper what we use in our day to day life paper was invented in second century B.C. and it was hydrocephalic until eighteen hundreds every day hundreds of people slowly started studying the hydrophobic properties of the paper but they always concentrated on the surface chemistry that is the first part of the equation they wanted to make the state a wife to be higher but as for the reasons I explained in the previous line. You can't get any higher with just by focusing on the right. So what happened with the knowledge what we had from the other super hydrophobic surfaces. We just added this extra component in that and made super hydrophobic paper. Let us first see how. We sat. How we how we satisfy these two properties getting a roughness and a low surface energy material getting rough. On paper when I was thinking about that first I came up with ideas like what not even going growing carbon nanotubes on paper or making some. For the little graphic on paper and many more at the time I took a course with Dr Harris. It's called a platinum processing course and that course I learned about the seven of polymer selective means you have almost first and Christmas in the minds of the polymers so when when you reach the polymer means what it what you actually do is feet away the polymer with some gas when you eat every the polymer with some gas. There are more first potions of the polymer H. faster then the crystalline parts. So I I got that strong concept and I when I was thinking about that. OK. Cellulose is also by a polymer and we know that cellulose amorphous and first in the mines. So I thought like maybe the oxygen plus Marvel H. my faith or a different rates are different parts maybe that can do roughness. And to my. To my product here. It's a more frisson Chrisman parts of the of cellulose or in nanometer scales which helps me to get the nano scale roughness to get the super high or for the city. Now the second point below surface energy material we did that by depositing a very thin film of pencil for eighteen using class more processing. We just get a hundred nanometer for you don't even see the film on the paper it's just so thin. This is the reactor what I use glass more reactor we all know that this is one of one of the important processes. Used in semiconductor industries to makes silicon chips right. Many people think glass more reactors are very complex very complex chemistry but let me let me get it now. I use this reactor right. We all use this reactor which is nothing but the force and light. You. Well wire if you take a wire you can conduct electricity through that wire instead of conducting electricity through that wire. If you can actually through a gas that's called last month. That's how you got to get those through isn't like. That's more it's known as a partially ionized gas. You can exhale tricity through the gas when you connect the electricity what happensis you have those gas molecules inside your system and friend. There are some some things. It's actually the gas molecule when it hits it it can either pickle Democrats from the gas molecule or it gets to get attached to the gas molecules. So you get ionization taking place and sometimes it's the gas molecule and it can break the molecule into atoms where you form radicals and sometimes the electron makes and other electron the gas molecule to go to Earth exacted stayed on the ground and we can offer a metaphor on that's the third part exaltation fluorescent lamp relates mostly on the exultation because the type of gas used in this lamp doesn't do of the big dust that are in a station and radical formation but it's not reactive The key thing is the type of gas. What we use in the reactor. If we use oxygen gas what happensis for for the paper substrates oxygen with if that before it forms C O two c go forwards and if that if the hydrocarbon in the people and the second step order used was the polymerization using friend offering it then what those versus the right products for this gas are not while it also it forms of them falling more full. Before getting on to my research I want to explain one more definition here which is called Contact angle history says when I want to drop rolls on a surface. The difference between the advancing and of the drop on the receiving end of the drop is known as the contact angle history says it is measured in the lab by incrementing volume of in a water drop by measuring that runs in contact angle and then they take out the water. From the drop and measure of the receding contact angles. I did the roughness and. And the thin film they both vision of which satisfies the two basic properties for the super Hydra for the city right. What I found was I got an advancing front act angle and receiving contact angle very close to each other. That is. When we had these two measurements the water retains its particle shape through of the experiment and that's why I think there is a very very little. And I'm going to play a movie for you here where the water drops roll soft on the first place if you cannot see on the. Extremely super hydrophobic so it actually is also from the surface then the in the next class of substrates. I wanted to see what is the effect on the roughness of the paper the natural roughness present in the paper you have a paper as a fiber webs which has some Micron scale roughness and each fiber by itself. It's not molecule or you smooth. So it has a nanoscale roughness on top of it. So this time I didn't use plastic action at all. I just used the definition to get a lower surface energy and for the roughness part I just relied on the natural roughness of the paper. What happened here is when I did that dancing contact angle measurements that dancing contact angle more freely than one fifty degrees which satisfies the standard definition for a super hydrophobic paper. So I can call this a super hydrophobic paper now but when I started pulling out water from the drop that the contact lent here you can see it's the same but the water drops became very very sticky to the paper. Which gave me a receding contact angle here. So you have what you have an advancing contact angle which is super hydrophobic and the receiving contact angle which is high for hydro fully So we really don't know how this was obtained and we couldn't name the subs. If we mean the substrate are super hydrophobic everyone think that the water will roll on the substrate and such a high history says value the one. Forty seven point two degrees what you see here has not been reported so far for any sort of faces. So we studied this in detail what we found was when you have our young contact angle a single contact angle value that is that once in contact sandal doesn't actually explain whether a but there are a substrate is what are Evelyn. Because what a ripple and see and super Hydra for the city are two different dorms super hydrophobia study just released on the younger contact found a greater than one fifty degrees actually form an equation explains more deep in more detail about how the water rose on a paper that is the water level and the behavior. This equation the left hand side of the equation is just a forced room which can make the water to slide on a paper or slide on any substrate with the inclination Alfonse and the right hand side of the integration is that he should turn this adhesion term doesn't give different on a single contact angle. It actually depends on the contact on the Vista rhesus one leaf the history says listserv and ten degree the water drop can roll off. If the history says is greater than simply it's very hard for the water drops roll off. And so I found these two substrates and I went to my advisors and said that he had got these two substrates one of the substrate is the role of substrate what we were actually expecting for I have one more substrate which is useless. It's having a higher contact angle to cheaters that it's super hydrophobic but it has a hydrophilic receiving contact angle. So I'm I said like I'm going to pursue in this direction and they said OK stop everyone is going there in that direction and they wanted me to go in opposite directions where no one goes. And I said like I came out of the meeting and said like OK let me proceed in that direction. And I did a little literature review on the History says values. What happens these terms what you see here has been published in the literature for the past thirty years they named different names for what ripple and sea and super hydrophobia city having histories as lesser than ten and also histories is greater than ten. So they didn't have an idea of why and how they can really name the surface water repellent or super water repellent because the history is greater than ten. Some people didn't even report the histories as values and still named their substrate equal and to super hydrophobic This made us to think that the knowledge about the history of histories this is very very important because the history says knowledge people get confused with the terminologies and you see a lot of terminology here. And what what we did was we proposed two simple definitions a roll of super hydrophobic and a sticky super hydrophobic which explains itself the role of super high traffic phobic has a contact analysts are going ten degree and this one has a contact angle greater than ten degrees. When we first when we wrote this paper. We we actually said all this work has been published and be criticized this work and I guess this paper went for review to some of these authors and we were pretty upset with the reviews but finally we were able to publish the paper. And I thought no one will cite this paper last week I found a citation for this paper but when I followed the citation I found out that it was from a member from Dr Hesus research group anyway thanks and how it. So hopefully I will get some people accepting Arthur Miller terminologies So we have the ideal Cassy see what I explain in the first slide ideal Cassy status you have voids between the liquid and solid there is one more state called Wenzel state invents I'll state what happensis the roughnesses. So big that the water can actually penetrate into the roughness. This vessel state actually has are very very high. History says that's because the water is getting into the into the substrate. So it cannot easily roll of it's it's got stuck. If it gets into the substrate. These are the two ideal staved States which has been the models for these has been for for sixty years that. Know with our super hydrophobic surface what what happens as I differ I define two terms here nano scale on microfilm Nana's what I mean by micro scale is the paper is very well fibers. So between each fibers the length scale use my count scale. And on top of each Freiburg I call it as a nano scale. What happens in the forests on a micron scale. The paper is porous so the water cannot doesn't go into the paper so you still have air pockets but on the nano scale. What happens is the there of the smoothly forward by the liquid that is the water hinders case. So you have a combination of winds and Kassie state when you have this combination what happens with this state gives a very high contact angle and the state gives a very high histories and this is the unique combination of a substrate where it has border states in it and that's what you see here this is a high magnification image and a low magnification image of my substrate. But when I do the oxygen plus my chin and create the nanoscale roughness on top of paper what you see here. These nano scale structure little nano scale features make Cassy state what nano scale on the micron scale and this is what giving the role of properties. Now we have these two extremes the sticky and super hydro role of the society so we have the boundary conditions the next step would be to get the intermediates to secure values. What we did was we really the etching time. And we used the same deposition found for all the substrates which made what it means by rehabilitation time and I'm slowly creating there an evolution of the nano scale structures. There are no nano scale structures at sixty minute searching there are an intermediate time I get the evolution of going on a scale structures. What happened here was exactly the same as what we expected. You have a sticky spot here but no aging and or all of sport here with sixty minutes searching and we could actually do in the history says what I mean by tuning the histories this is I'm assuming the adhesion of the water drops but if you see the contact angle that advancing contact handles all rays it's about one fifty degree. So having an advancing contact angle greater than one fifty degrees. I could I could tune that he should of that drop to the substrate independent of the contact angle. And finally be plotted the this is contact Angle vs contact angle history says. Remember I was stalled my or my advice was that I shouldn't look for the role of super hydrophobic I should look for the sticky super hydrophobic if they didn't tell me that I would have got stuck in this cage. I doubt there were more and more roll of super hydrophobic surfaces and I would have been here. But since I took another direction which was very very different and high risky to what happened. We ended up in developing a substrate a breakthrough substrate which has a high contact angle but still it's very very sticky and also we can vary that he should force by tuning the process. Sam eaters. In the conclusion the. The Please let us see what will. What would be for the role of super hydrophobic surfaces. It can be used for static transfer of fluids. That is. You can have a water drop you can take a substrate you touch it. The water drops to the substrate and you can transfer it and. Transfer it to the tree which which is which can be used for robotic supplications and it can we call it a freezer for water drops and it can also be used for microfluidic devices. So the take home message here is the paper. It's hydrophilic here. You can see the relationship between the liquid and the on the paper it's like. The liquid considers the paper as a bird friends. It's like the bird from its height of fully but here it's like after breaking up. It's running off from the girlfriend it doesn't like it at all but this one the sticky surfaces and I guess just what relationship this would be. It's like after getting married right. Even if you don't like the substrate you want to be there. You can't run off so. That's a conclusion and Ike that's one of the slides while you are enjoying these movies I can take up any questions you may have. You know what happens when you run your comments. When you can answer water drop what happens is you get water even between the nanoscale roughness and what you formless of no matter how big or how small your water droppers people have studied condensing water drop on notice leaf which is a super hydrophobic so face what they got was with the condensing from the drop this very small so that the length scale of the drop is not high enough to be the roughness get this the. It's always in the state. So this is always high for a condensing drop drop. But once once you get more and more convincing if the drug goes grows very big then it will from out and it can be the surface. Yes exactly. So that's a question we get from most of the people so plastic processing is it's a technique used in some iconic or industry to process a very expensive saturate that is the silicon wafer when you process the paper there the the one of the problem. What the paper industry would faces the biggest problem is the vacuum. What we are using we run these experiments at very high vacuum we run this one tar and to get a very big plasma reactor for the paper industry to run it at once or it's tough but there is an alternative. There are flats most which can run it at most British pressures and we believe that the process of the experimental would be similar to what we use but we don't have an extra pressure reactor in our lab but still we would like to try it out. Not in my fourth year but maybe here. Yeah. Yeah there. What are ozone we haven't tried that if I do I assume that the ozone will also work it has the oxygen radicals right. So it will also eat the paper and make carbon dioxide and water. So probably the ozone will also work when when you talk about the chemical treatment. There can be chemical treatment but when you think about the paper. You cannot defeat the fever to do a treatment so if the strips. All the fibers inside what are treatment it's just on the nano scale which. Stroeve. The first layer of fibers. That's the first layer of fibers doesn't experience anything other than the first few nanometers. Yes exactly. So what what happened for the surface. I took all these substrates I think all the such traits on a plate for the substrate even when the plate just want one eighty degrees inclination the subs this quarter dropped in roll off this roll for the substrate even with the one degree inclination it rolled off for this substrate I had various inflammations like forty five degree inclination ninety degrees something like that definitely that he forces different for on the side. Here. Yes So I told about one which was the reserve for water drops. So the trees are for water drops actually the extremely sticky. But there are intermediate stickiness right for that you can you can control the mobility of the water drops for. We don't have exact idea but for microfluidic applications where you want the water to try to be transported you can control the angle of inclination and control the transport of water through that so. You have but we haven't explored that. And also one more thing is there are protein and proteomics micro Ari's where they place small drops of water close these are probably they can use the sticky substrates for that you can have a higher concentration of drops so that you. Will increase the resolution of the pretty of proteomics studies what you do. So. Exactly. So definitely we need to go from a higher sticky surface to our low sticky surface what what I did with this experiment was I placed a water drop on the substrate and OK I placed a water drop on the substrate and I could carry the water from by the substrate No I placed the substrate and the. Upwind of the hell that's that's that's for sure. You cannot go down. The that's a very good question. Fishing what happens when the plasma pollen polymer is falling but I think for most after you take out from the plasma reactor the firm still has some radicals on top of it when it has radicals you expose that blood must be and you have oxygen atoms and that most people can you can absorb right. When you have oxygen atoms of course you're going to make it ahead of fully. It's void just for that reason their reaction at one thousand degrees so height of the temperature. So whatever radical that is formed on the surface will get eventually quenched by the gas even before we take it out so we we have tested the paper like so I started this research like two years back. So I have a paper. I made two years back and it's a supervisor for me so I know that time frame for sure.