 Welcome back to this course on nano structured materials, synthesis properties, self assembly and applications. We are in the module 3 and this is the last lecture of module 3, the 12th lecture and we are discussing nano composites. The subject of nano composites we started in the previous lecture and today is the second lecture for nano composites. So briefly we discussed in the last class that composites are a mixture of two or more metals or ceramics or metal ceramics which do not form a single compound or a solid solution. They are separate entities but mixed very vigorously and intimately to give you a structure where if you look at the x-ray diffraction patterns then you should be able to see the different phases which form the composite. If the phases which are making the composite are crystalline then you will see all the phases in an x-ray diffraction pattern or even under electron micrographs. However, if you have a polymer and one crystalline material forming a nano composite then you may be able to see a broad hump of the polymer and a sharp lines for the crystalline material which is forming the nano composite. So there are different types of nano composites which we studied which can be one metal in a ceramic like an oxide it can be gold in Ti O 2 or silver in Si O 2 or it can be a polymer with another polymer or a polymer with a ceramic or a polymer with metal nanoparticles. So wide variety of composites are possible and it is not only two materials that can be mixed to form a composite you can have three four different materials to form a composite and we discussed that why composites are important. The most important part is that composites give multifunctionality. So if you have three individual components making the composite then you get three different properties are possible to be present in the composite which you make and specifically when you are talking about nano composite how is it different than normal composite is that one of the ingredients should be in the nano dimension. So when you are taking two or three different materials one of the material has to be either a nanoparticle or a nano wire or a nano plate. So one component of say binary mixture of components or ternary mixture of components yielding the composite should be nano size then you get a nano composite. So today we continue on the second and final lecture of nano composites. So today we will discuss some composites which are made of carbon nanotubes and polymers. Carbon nanotubes as we have discussed earlier in this course are can be of different kinds they can be single volt, multi volt and basically they are nano in two dimensions. The third dimension can be very large because it is a nano tube. So it can be 100 micron, 5 micron, 10 micron and certainly more than 50 to 60 nanometers whereas the other two dimensions of carbon nanotubes depending on the number of nanotubes in a bundle can be of few nanometers to 20, 30, 40 nanometers. So when you mix these nanotubes of carbon with polymers different types of polymers you can get different properties depending on whether this is a semiconducting nanotube then you will have semiconducting property incorporated into the nanocomposite with the polymer and the polymer will be giving it strength or ductility etcetera for applications. So combinations of carbon nanotubes either semiconducting or metallic carbon nanotubes with polymers are known and they have different properties as we will discuss. Then a very fascinating material which is of interest in recent times is graphene. Graphene is one layer of graphite. If you take graphite which has got several layers made of carbon hexagonal rings of carbon and the layers in between have very weak van der Waal forces. So this layered structure of graphite if you can remove one layer from graphite then you get graphene and graphene is very exciting because of its high mobility of electrons and graphene is known as a Dirac solid and it is it has got tremendous applications. So people are trying to make graphene polymer nanocomposites. So here graphene is a two dimensional sheet. So it is like a nano plate or a nano sheet because one dimension in graphene is in nanometer. So it may be one nanometer or two nanometers that depends on how many layers of graphene you have. So graphene polymer composites will give you the functionality of conductivity of graphene and many other properties of graphene in the polymer and the polymer is basically to stabilize this graphene and the nanocomposite becomes mechanically robust. Then you can have polymers with silicate materials. So there are several silicate materials some are naturally occurring some are man made a large number of ores of silicon are basically silicate materials. Even zeolites are alumino silicate there can be many many silicate based on magnesium strontium etcetera which are available in nature and which can also be synthesized in the laboratory and when you mix these silicate with polymers you get different types of nanocomposites. So coming to the first class of nanocomposites which we are discussing today is a blend of carbon nanotubes and polymers. So what are the benefits that carbon nanotubes can give to this nanocomposite as I mentioned some of the carbon nanotubes are highly conducting and those carbon nanotubes are metallic and they give high electrical conductivity. So the nanocomposite made with such carbon nanotubes will show such high electrical conductivity. Then you can improve mechanical properties the mechanical strength you can improve thermal conductivity you can enhance the thermal stability by making composites with polymers enhancement of oxidation stability and it can be used as a fire retardant when you mix nanocomposites of made from carbon nanotubes and polymers if you choose the right polymers you can have composites which are fire retardants. Now the very high aspect ratio of carbon nanotube leads to properties at very low concentrations of carbon nanotubes. So with very low dopant of carbon nanotubes you can get excellent properties because of the very high aspect ratio of these nanotubes. The aspect ratio is basically the if you take the ratio of the length and the breadth of the nanotube then that is called the aspect ratio and the longer the tube and thinner the tube you will have a higher aspect ratio and the high aspect ratio allows you to add very small amounts of carbon nanotubes as dopants, but the nanocomposite have has very enhanced features on properties which have been listed here and discussed like electrical conductivity thermal conductivity etcetera. Now how do you introduce carbon nanotubes into these polymers? So one of the methodologies is that you suspend these nanotubes in polymer solutions and then you can spin code them to make thin films. Of course, there are various other methods of making thin films, but this is a simple methodology you suspend them in the nanotubes in solution and spin code them or dip code them on substrates of your choice variety of substrates you can use and depending on your spinning speed and the concentration of the nanotubes in polymer you can vary the thickness of these thin films. This is one methodology otherwise you can do in situ polymerization. So you have nanotubes and you start with the monomer in the solution mixed with the nanotubes and then you do the polymerization in situ in the presence of the nanotubes. So then you will have a good mixing of the nanotubes in the polymer. The other is you do a melt mixing of nanotubes you take nanotubes and take a polymer and then you melt them and then allow it to cool and that is called melt mixing of nanotubes with polymers. And one of of course, you have to optimize the best nano composite will be those where the dispersion is very high. That means the carbon nanotubes has to be dispersed very well throughout the polymer matrix and the method chosen depending on your polymer and depending on your concentration will make this dispersion will be dependent on this dispersion will be dependent on the methodology and the concentration which you choose. So because this is generally a problem how well or how homogeneously you can distribute the carbon nanotubes on in the polymer that is a key point and you have to optimize methodologies such that you have high dispersibility of the carbon nanotubes in the polymer matrix. So this is an example of melt mixing of carbon nanotubes with the thermoplastic polymers. So you start from a master batch of a polymer which is a highly concentrated polymer with 15 to 20 percent of carbon nanotubes and you can and then you directly incorporate from solid pre mixtures of polymer powders nano granules with carbon nanotubes. So and then you melt it. So when you melt it then you get this nano composite depending on the master batch there is the master batch that you have. And if you start from a pure polymer you have this kind of features of the pure polymer and these are the carbon nanotubes. So depending whether you are starting from a master batch which is a highly concentrated batch of polymer mixed with carbon nanotubes you get this kind of which has a disc kind of a SEM picture of the master batch and this is the pure polymer and this is the nano composite that you get. Here you have started with CNT and solid pre mixture of polymer powders and these are the CNT tubes and this is the nano composite that you get. So melt mixing of carbon nanotubes with thermoplastic polymers can be made in this way and this is the nano composite these are scanning electron micrographs of nano composites. Now this is an application of graphene with the polymer to form a nano composite and this kind of nano composite has been shown to kill bacteria on surfaces. So graphene can kill bacteria and also prevent the formation of pathogenic and corrosive microorganisms and so it is a very important material or candidate for antimicrobial coatings for surgical equipment and various kind of tools which are used in hospitals and especially where there is going to be a contact with a either blood or an organ where there is probability of infection if bacteria is present. So this graphene polymer nano composite coatings do not sustain bacteria and hence they if they are coated on top of such surfaces of blades etcetera which are used in surgical equipment then it provides that security against bacteria and graphene can be hard to process on its own because graphene tends to agglomerate or clump together and hence one of the ways of getting around this problem of aggregation of formation of these clumps is to mix the graphene with polymers and you have to choose specific polymers and the choice is such that the dispersibility is high. So you want to disperse the graphene very readily in the polymer solution and then coat the surfaces effectively. So that is the choice as to be optimal to get very good coatings of these graphene nano composites on surfaces. So this is a proof of the enhanced bactericidal properties of graphene so the polymer is enhancing the properties of graphene. So if you look at a pure graphene that somewhere here and the pure graphene acts on E coli and you can see that is around 70 percent toxic to E coli the toxicity is there. Whereas for another microorganism B subtilists that is little higher now you can add sample solution. So you have different types of sample solutions so and you will see that there is an improvement in dispersion of graphene by the polymer p v k and you see the toxicity levels come down when you have certain concentrations. So if you have p v k this is the pure polymer right it has it is not toxic to the bacteria and this E coli and subtilists graphene has toxicity of around 70 percent. Now when you have this mixture of p v k and graphene so that is p v k g and these are different sample solutions. So you see that for certain solutions the activity is very high nearly 97 percent that means this mixture 1 of p v k that is the polymer and graphene is 97 percent toxic which is higher than pure graphene which is like 70 percent toxic. So that toxicity towards these microbes has been enhanced when you coat graphene when you mix graphene and p v k together individually p v k is a very poor material the polymer is not toxic to these and graphene is toxic but with the toxicity level of around 70 percent. Now you also see that when you make the polymer graphene composite p v k g composite you can see that the AFM shows you the kind of dispersibility of graphene in the polymer is quite uniform and this is friction measurements on the surface of this composite which also shows quite uniformity in this and homogeneous surface. So the optimal coating of graphene with p v k a polymer can lead to much higher toxic levels for these microbes and which is helpful for applications in medicine. This is another example of a nano composite of graphene with an inorganic material. So this is zinc sulfide and zinc sulfide graphene nano composite can be used for several properties especially optical properties. So here this is the TEM the microscope pictures of graphene oxide and zinc sulfide graphene nano composite. So from graphene oxide you add zinc ions so a solution of zinc and a sulfur source and then this graphene oxide is mixed with this sulfur source and zinc ions in a hydrothermal bomb at 180 degrees when you heat a hydrothermal bomb which is a kind of a teflon container you have inside a stainless steel bomb and then you close the lid. So there is a autogenous pressure which develops and that is called a hydrothermal reaction and in that reaction zinc sulfide is formed and it spreads homogeneously on the surface of graphene oxide which becomes graphene under these conditions. So both zinc sulfide forms these particles as you see and this layered material which shows this kind of crumpled nature is graphene and this is a nano composite of zinc sulfide and graphene and the property which you are interested in in this kind of nano composite is the optical property and so you look at surface enhanced Raman scattering for graphene oxide and with pure zinc sulfide and this nano composite. So you compare the surface enhanced Raman which is SERS surface enhanced Raman scattering is a very important technique and there you see that the nano composite displays enhanced scattering and you can see fluorescence enhanced property compared to pure zinc sulfide. So the SERS activity you compare with graphene oxide and for the nano composite it is much higher than for graphene oxide and the fluorescence enhancement you compare with zinc sulfide again for the nano composite enhancement is much larger. Now this is another example and this is an example of gold nano crystals on silica. So here the nano particles are of gold and they are crystalline nano particles and you the matrix is silica that is SiO2 and together they form nano composites and so what you do is you start with your gold which can be metal here we are discussing with metal and you can have different processes to get different properties. So here you can see that phospholipids have been coated on this gold nano particles assuming a is gold nano particle you have phospholipids on that and phospholipids are water soluble. Finally you can have this gold particles capped with surfactants and that is what it shows and then you can use catalyst to make a silanol layer on top of it. So the silicon hydroxy groups you see they are on top of it what these do is they make this nano particles water soluble. So these are water soluble and here also you can make the water soluble etcetera. The other thing is that you can make this silanol group capped gold nano particle and into a film using spin coating and you can make devices out of them or you can self assemble them and make a inorganic solid. So you can have this face centered lattice of these particles using self assembly. So different processes are there which have been shown here of gold silica nano composites. So silica is formed on top of gold starting from this silanol groups and when they self assemble you can get this kind of particles and here also you can do self assembly and get these particles which you are seeing of gold particles and since gold has a plasmon resonance you can measure the absorbance in UV region visible region. So this is an absorption around 500 nanometers and that is why you will see gold nano particles give colored solutions. So it depends on what is the size of these gold particles you will have the absorption maxima at different parts in this region. So it can be absorbing at 500 or higher wavelengths or lower wavelengths and hence the color which you see of gold particles will be changing with the size of these particles. So you can make gold silica nano composites by several methods and so the primary layer is the gold which has a particular thickness d p and then you have a secondary layer which has a thickness d z. So these thicknesses define the thickness of the core and the shell if it forms like a core shell you can make not only core shell particles you can also make simple nano composites of gold and silica. Now what are the advantages of nano sized additives there are all the properties that you can think of can be improved and it has been seen substantial improvement are there for example in the mechanical properties of nano composites because you have these nano particles which are in a matrix and this matrix can be of a polymer or of a ceramic which is a inorganic solid the strength of the composite will become much higher when you compare with the strength of just the bare particles put together. So the matrix gives it certainly several properties but the most important property most of the matrices give is the mechanical strength and the stability. So the mechanical properties the strength the modulus and the dimensional stability all are enhanced when you make nano sized additions to a matrix. Then the porosity is decreased and because of decrease in porosity the permeability of gases water and hydrocarbons is decreased. So and this is very important when people are trying to make films for packaging. So if you want to make food packaging or any other kind of packaging when you use films to keep materials fresh or to keep materials secure from microbes or temperature variations or pH variations you need some kind of a surface which protects that material. And such nano composite films are a big application it is a big huge industry of nano composite films for all kinds of packaging especially in food packaging and in making coatings in bottles which have to keep especially medicines and food. So there is a tremendous industry of packaging where such nano composite films or plastics are important and essential. So we mentioned about permeability of gases water hydrocarbons very important for storage of food and liquids for edible purposes or medical use. Then thermal stability and variation of heat this is again choosing the right nano composite film you can maintain high degree of thermal stability. Then flame retardancy so material which will not catch fire that kind of nano composite film or coating has to be put on surfaces where the environment may reach temperatures which are above the ignition temperature of the material and you may lead to a fire. So if you coat these kind of nano composite films then you can have flame retardancy and you can also have reduced smoke emissions if you are having the right kind of film to control the carbon particles which are coming out with the smoke. You can design nano composites which are highly resistant to acids or alkalis you can give a different finish to surfaces this is especially important in the automobile industry where they are coming up with newer and newer coatings on the surface of vehicles to give a very fine finish. Apart from a very fine or shiny finish they also want to make these nano composite coatings on these automobiles such that the surfaces are scratch resistant. So scratch resistance is a very important thing in automobiles and for that several nano composite films have been developed which enhance the scratch resistance and those are very important in automobile industry. Then in certain applications you need highly conducting surfaces. So you have a nano composite film say of carbon nano tubes which are conducting carbon nano tubes on a polymer. So you have a polymer carbon nano tube composite nano composite which is highly conducting and such coatings or such materials are required wherever you want electron transfer or current carrying capabilities you need such coatings to be made on those surfaces. Finally, you have in some cases to need optical clarity for example, if you are making certain lenses and you need optical clarity or you are making some prisms for optical data collection. So in those cases optical clarity is very much required that means the transmittance has to be very high and many conventional or normal polymers filled with certain normal cheap materials which are used or which are there in the industry have been shown to lower the transmittance. And so there are now many new nano composite materials of nano particles mixed with polymers which form materials of great optical clarity. So you can really have improved optical properties based on nano sized additives. Now what is the disadvantage of nano sized additions? The toughness and impact performance for example, nano clay modification of polymer such as poly amides in some cases have been seen to reduce the impact performance. So many poly amides if you use it like for a coating which will resist any sharp attack by a shrapnel or a bullet then it has been found that nano clay modification of those polymers can reduce the impact performance. That means when a projectile hits this nano composite then what is the impact of the poly amide which is a polymer? Several polymers are known which are very tough and have been used for making bullet proof vests etcetera. Now it is a possibility that some of the nano clay modified polymers can have lower impact performance. Then the nano side addition or nano composite formation for application where you have impact loading there also you have seen people have seen events where there is a reduction in the impact loading. So there are possibilities where although many properties improve due to nano sized addition there may be few properties which are kind of at a disadvantage when you add nano particles. So one has to choose the optimal solution and has to prioritize which properties are more important for a particular industry and according to that one has to optimize whether somebody is ready to forfeit some of the advantages of keeping the polymer as such without adding any nano particles or you gain a lot in some properties which is beneficial to you by adding that nano particle. So you have to see the application for which the nano composite is required and then you design whether you need to add nano particles to the matrix. Now this is an example of a material which has been made in a company called TNO company in the Netherlands and this data is related to poly amide Montmorillonite which is a clay so it is a poly amide polymer clay nano composite. Now in this polymer clay nano composite there is tremendous improvement in the tensile strength. So this report of this company showed that the tensile strength improves nearly by 40 percent at nearly room temperature and if you increase the temperature to say 120 degree Celsius then the improvement is still there however it goes down from what it was at room temperature. So from 40 percent at room temperature it becomes 20 percent at 120 degree Celsius but still it is much higher tensile strength than the poly amide by itself if you do not add this clay nano material. So this Montmorillonite is a clay and is a the nano dopant here. Now it has also been seen that modulus improves by 70 percent and 220 percent at the same temperature for the nano clay modified material. So so much improvement of modulus can be find for this nano clay modified material. Then the loading of Montmorillonite K is only very small amount you need a 5 percent loading to see these kind of improvement in the properties and similarly in another polymer PMMA that is the short form of poly methyl methacrylate when you mix this polymer with a clay and make this polymer clay hybrid or composite then mechanical strength improves just like in this case of poly amide Montmorillonite nano composites. According to some other applications so mechanical properties we discussed further in automotive and general industrial applications also many of the auto parts are now made of nano composite materials and these typically are used as mirror housings. So if you see on the rear view mirror the side view mirror there is a kind of a cover on in which the mirror is a kind of placed. So that material is normally a nano composite in the better cars today and those mirror housings then door handles engine covers and timing belt covers most of these people nowadays are using nano composites to make these materials in the automobile industry. In the home appliances sector also many traditional materials are being replaced by nano composites. So for example you have blades various types of blades are there fan blades are there blades for vacuum cleaners blades for power tool you know you have this power drill that has a housing. So that outer casing of the power drill is made of a nano composite which is very high strength and durable then lawn mowers you have your lawn mower and they have a hood and this hood nowadays is coming with nano composite similarly covers for portable electronic equipment like mobile phones pagers etcetera. They have this cover which is not metallic which is mainly nano composite today earlier it could have been a polymer or a metal nowadays most or a composite now you we have nano composites which give you high strength may be lighter to make housings or covers for electronic equipments. Now further applications two important applications of the nano composites one is the gas sensors and second is packaging because this also has to do with transport of gases in a package where inside some material is there depending on the material you want either no entry of gases or you want selective entry of certain gases. So this permeability of the polymer film or the membrane is very essential to be controlled in packaging industry similarly gas in gas sensors you have to control or you have to have maximum sensitivity and for a particular kind of gas. So the gas barrier property improves from incorporation of small quantities of nano clay materials there are several nano composites which have been found where you have this kind of packaging and as I said in packaging in the food industry it is very important for covering say processed meats cheese confectionery cereals and many items where you have the raw material inside the bag and you just boil the bag and then open it. So in this kind of cases there has to be certain property of the membrane which is outside the material which helps in keeping this processed food intact safe without attack from microbe and if it requires certain environment say it needs a nitrogen atmosphere then that remains intact. So all these things are very important for the meat industry cheese industry milk industry for fruit juice industry for all kinds of dairy products for carbonated drinks the bottles have to be coated with something you have this kind of a polymer bottles and they can be made of nano composites. So these are great applications for nano composites and food packaging is an industry which has tremendous growth and is of tremendous importance where nano composites play and will play a very important role. Now there is tremendous application of nano composites in the fuel tank industry for example in automobiles you have this fuel tanks and you can make nano composites where you have incorporated nano clay in a polymer network. Now these kind of nano composites have been shown to reduce solvent transmission through the polymers. Now many of these polymers which are normally used are polyamides and the incorporation of nano clays as fillers reduce the solvent transmission through them and so they retain the solvent or the fuel for much longer time. And this kind of nano composite where you have a polyamide 66 polymer with a nano clay filler like montmorillonite or other nano clays bring about a significant cost reduction due to the economy being saved because of the solvent being less transmitted through the fuel tank. So it is retained in the fuel tank for much longer period of time. So this is one of the major applications in the fuel or the tank industry and it can be used for storage tanks it can also be used for many other types of tanks not only in automobiles. So you can use such nano composite coatings on even overhead tanks where in industries where they are retaining certain solvents and especially large industries in the petrochemical industry where they have very large tanks to store solvent you can protect the solvent transmission by having nano composites as a coating. Now several films like in the packaging industry you can make nano composite based films you can also make films where the importance is in the optical transmission. So you can add fillers at nano levels which has significant effect on the transparency of the film. So you increase the transparency of the film by increasing the content by adding nano dopants and you can also reduce the haze in the film and several films are required where you need high transparency and reduced haze. Now nano modified polymers coated on polymer polymeric transparency materials you can also enhance their toughness without interfering with the light transmission. So you want to make the film much more stable much more mechanically stronger but you do not want to affect the optical transmission and such nano fillers are known where you can add them to those polymers and you get both the properties of enhanced strength without cutting down on the light transmission. Now similarly you can have other applications in using nano composites for example you can have a dual property of high velocity impact resistance combined with aberration resistance in the same nano composite and this was demonstrated by a company called Triton systems in USA where they showed how that nano composite can prevent a high velocity impact and also prevent aberration. Now another class of nano composites is the polymer silicate nano composites. So you have a polymer and you have an inorganic material like a silicate there are many types of silicates both man made and naturally occurring and hence they can be very economical to make nano composites with. Now if you have an organic polymer embedded in an inorganic matrix without any covalent bonding between the components then you can have one kind of nano composite. However, you can also have organic polymer with inorganic matrix where you have covalent bonding between the components. So that is also possible similarly there is another class of polymer silicate nano composites where you have coformed inter penetrating networks of inorganic and organic polymers without covalent bonds between phases. Then in this case there is no covalent bond then you can also have the other way where you have covalent bonds now with between the phases between the inter penetrating networks of inorganic and organic polymers. So you can have with covalent bonding and without covalent bonding these nano composites and then you can have non shrinking simultaneous polymerization of inorganic and organic polymers. So both normally we think that you make organic polymers by polymerization but you can also make inorganic polymers and if you can simultaneously do the polymerization of the organic and the inorganic polymer then you get another type of nano composites or you can get nano composites through another methodology. Now simply speaking this making nano composites of silica, silica based nano composites or many others titanium based nano composites they all go through a two step reaction the first step is the hydrolysis and the second step is the condensation. This is a large majority of the nano composites which use alkoxides as their starting reagents like in this case one wants to make silica as the inorganic component of the nano composite. So you want to incorporate silica so you start with the alkoxide which is tetra ethoxy silane. So when you use tetra ethoxy silane first step is the hydrolysis so you can have basic hydrolysis acidic hydrolysis depending on the process and you get this kind of a silanol groups and then these silanol groups lose water molecules to form Si, O, Si linkages. So that is a condensation of two silanol groups and water molecule is ejected and you get this kind of Si, O, Si linkages. So this is the condensation process the overall process can be written as this tetra alkoxy silane with water in the presence of acid base or salt as a catalyst and then you get silica or silicates depending on other metal ions present. So these are general scheme for hydrolysis and condensation and has been used largely for making silica nano composites or titanium nano composites and also in recent days on other type of nano composites of niobium and tantalum etcetera. Now this is another mode of synthesis of nano composites where you take this base acid or salt catalyzed polyphosphazane. So this is an example or polyethylene oxide. So these are the polymers and then you dissolve this polymer in T H F and ethanol T H F is tetrahydrofuran and you take a mixture T H F ethanol is this mixture is the solvent and the polymer is dissolved in the solvent the polymer can be one of these above polymers or something different and then once you add this T E O S the silane precursor or the silicon precursor and the catalyst to cause the polymerization or to cause the reaction the hydrolysis and condensation. Then the mixture is capped and sonicated and the solution is aged from hours to days in a vial and poured into a Teflon mold and it is loosely covered at room temperature. When you do that since it is loosely covered the solvent will slowly escape and the nano composite will form by self assembly it will self assemble and the solvent will escape during the condensation. Now the silicate polymer nano composites that we are talking about so we are talking of basically silicates here because we are talking of silane as the precursor and so this is a process you started with T E O S. So you are looking at silicate based polymer nano composites and so the applications of these polymer silicate nano composites two major applications one in lithium batteries which is you know one of the most important areas of research and development for the industrial world because of the energy crisis. So lithium batteries is a very important area and solid polymer electrolytes are required for lithium batteries. So this is one of the rich area where these polymer silicate nano composites are required and are used as electrolytes. In another application in the automobile or the transport industry in tire manufacture you require fillers where these nano silicates have great reinforcing power. They are added in the to substitute carbon black normally carbon black is added as a filler but these nano composites have much better properties. They give much better properties to the tire like improved tear strength improved abrasion resistance they go for much longer time and they have much better addition properties than carbon black. So there are two industry one is in the energy sector the other is the transport sector where these polymer silicate nano composites are of great use. Now so with this we come to the end of today's lecture that is lecture two of nano composites and with that we also come to an end to the module three and you may look for the last two lectures into these references and in these references the some recent work in journals have been given and some books which are books and like this and like this these are books and these are review articles which give you some idea into what is been done in the area of nano composites over the last 20 30 years and with this we come to an end to these our lectures on nano composites and we will start with module four where we have two lectures and where we have 14 12 lectures. So we have finished 28 lectures with module three and we have 12 lectures remaining to be done in module four. So thank you and we meet in our next lecture.