 In this lecture, we will learn about self-assembly. It is nothing but organization of structures to form a higher level structure. So, how do we do that? We will see upon this particular lecture. So, we can see self-assembly is nothing but spontaneous and reversible organization of molecular units into some ordered structure. So, there is some order which basically is incurred by this particular entities, molecular entities which is very spontaneous in nature and it is also reversible as well. And since it is spontaneous and reversible, it also acts on a very localized level. So, in this case, we are building nano structure and it starts constructing itself or it builds itself. So, we see molecular units, they go on to forming certain organizations and it is self-similar and it starts constructing itself. At the same time, there is a key role of weak interaction. So, weak interaction such as Vendor wall forces, capillary action, capillary forces or pi pi bonds or the hydrogen bonds, they tend to also provide secondary stability to the particular unit or to particular organization to get higher level of order. And it eventually goes on to forming such as molecular crystals, self-assembly, monolayers, thioles and many other. So, we can see self-assembly is nothing but spontaneous and reversible organization of structures, molecular units to form little bigger structures and these are self-sustaining and it means that it is constructing itself as the process goes on. And there is very much key role of weak forces such as Vendor wall, hydrogen bonds, capillary forces because they also tend to provide certain stability to the nano structure and it eventually goes on to forming more ordered structure such as molecular crystals, self-assembly, monolayers and so on. So, seeing that self-assembly monolayers, first of all they are highly ordered structures. So, their nature is highly ordered and it provides very tight packing and it forms very rapidly on the surface, but to attain a particular order, it that is the time consuming step or that is a step, the rate deciding step, it may require up to 15 minutes to achieve a well ordered and defect free self-assembly monolayer. Its applications involve chemical sensing, wettability, controlling friction, corrosion protection, even patterning or even semiconductor passivation. So, we can see that in self-assembly monolayer we have substrate and that substrate is covered with certain head groups and which is a tail region and they go on to becoming much more ordered and they might have certain functional group on the top of their chain to order a to render a certain functionality to the. So, we can see that this is nothing but some sort of a functional group. So, we have a substrate over that we tend to deposit certain head groups that will attach itself to the substrate when it has a tail region. This is the tail region and then that tail is covered with again with certain functional group to impart certain functionality. So, we can see that they are much more ordered in nature that they are very nicely ordered and they are tightly packed. Also, they can form very rapidly on the surface, but to organize them into very ordered structure it requires much time because they have to come and then basically confirm to the forces which are acting around it to render a very ordered and a defect free self assembly monolayer. You can see that for switch or logic devices we need many functional units on the surface. Currently, we have around 10 to power 8 units which are there on a per centimeter square area and depending on this confirmation it can go as dense as 10 to power 13 units per centimeter square. So, we have a possibility of increasing this number of this density of this functional change by order of 10 to power 5. So, that is the logic we are talking about we can enhance it by 10 to power 5 times or 1 lakh times to render a certain density to this material and impart much more functionality to even logic devices or switch devices. Their application also include chemical sensing because if we have more number of such pattern surface on a particular substrate then we can sense a particular gas or a media or any chemical functionality to a very high level. So, we can even when there is a very small PPM of a particular gas or chemical we can sense it. Also, utilize for either increasing the wettability or reducing the wettability for controlling the friction if we can impart certain layers which are much more resistant which can provide as lubrication or non adhering property. We can also provide corrosion protection to a surface we can have certain pattern structures. So, if we have certain functionality and that functional groups will come the had groups will come and adhere to a certain region and then we can achieve functionality through those functional groups by this particular monolayers and also it can be utilized for passivating the semiconducting surfaces. So, again there can be two approaches first of all bottom approach or the top down approach, but the overall idea in the bottom approach is we control something at a molecular level and then say if you have certain molecular level then we can impart certain micro structural pattern to it and then that micro structural pattern can again have certain nano structured pattern. So, we have nano pattern over a micro pattern. So, we have substrate then we have micro structural pattern over it and this is a nano pattern. So, if we are starting from a nano pattern then we go on to constructing a micro pattern and then we deposit this micro pattern on a substrate then we can basically we are going from a bottom approach it means we are going we are combining couple of functional units molecular units go on to forming certain nano structures nano structures go on to forming a little higher level of micro pattern and then that eventually is getting deposited on a substrate. Now, this is very useful in imparting certain functionality to a material. So, if we have this sort of scalability or length scale associated with that we basically are going from nano structure from a molecular structure to nano structure to micro structure to impart certain functionality that is nothing but bottom approach and how can we utilize them we can play either with the surface tension or the surface free energy. So, in this case if you play with the functional group we can provide either complete wetting. So, we can provide much more wetting to the surface or we can also provide non wetting to the surface. So, if we can control the functional groups to be coming out to be as say O H minus then it is very high affinity for water. So, now we make the surface hydrophilic in nature, but in another case if you take a methyl group then methyl group will try to repel it and because of that it can reduce much more non wetting or hydrophobicity. So, we can see that methyl can have hydrophobic nature and that this alcohol O H minus can have much more hydrophilicity. So, we can somehow we can if you are playing with the surface tension or surface energy we can impart a very different functionality of the surface. So, bulk is same, but only because of this functional unit if it is alcohol group it will have much more hydrophilicity if it is a methyl group it can have much more hydrophobicity. So, by playing with the surface energy or the surface tension we can somehow impart very different or contrasting characteristics to a substrate. The substrate is the same, but only because of its surface we can control the overall functionality of this particular surface or substrate. So, we can again go by either top down approach or a bottom approach. So, in top down we take a bulk and we start fracturing it until we reach nano. So, in this case we are trying to break up the material we break the material to achieve a finally nano structure which are approximately couple of nanometers in dimension. On the other hand if you go from molecular units if you have molecular units they go into forming certain nano structures and this can be achieved by imparting self assembly. So, now we can we can we can get from molecular units we can get microstructure in one unit, but in this case we are breaking the material. So, there is much more wastage of material, but in this case we achieve everything in single step because of the self assembly. So, in the process what we are doing we are saving the material as well. So, in this case again we are able to reach a couple of nanometer, but we are starting from molecular units which are sub nanometer in nature and then because of self assembly we can get structure which are couple of nanometer. So, what we are doing the final product is the same that we are achieving certain nano structures, but one is this is the top down approach and this is a bottom up approach. So, we can see in top down approach we take a bulk material which is very big in size it can be couple of meters to to to that level and basically we are just breaking the structure and in the process we finally get which is a nano entity, but in bottom up approach we go from molecular units we allow it to self assemble and then we get a final nano structure and that is again nanometer in size this is a single step. So, we basically tend up saving the material because we are starting from a entity which is much more smaller than a nanometer and this gives us the advantage that we can also somehow control the overall assemblage of this particular system from molecular units to a bigger structure. So, we can see first of all we have a head group which is lying on a substrate. So, we have a substrate then we have a head group with certain tail and then a functional group. So, we have head and this is a tail or this is also called a spacer. So, depending on the length of this tail we can somehow control the how this structure will come out to be. So, in one case we can make the surface highly wetting or non wetting. So, we can make either wet or non wetting surfaces just by controlling if it is alcohol or if it is methyl. So, if we can somehow control this particular part we can control the nature of wetting or non wetting. At the same time what we can do we can also play with the chemical functionality. So, in this case we can make it physically either attractive to water or repellent to water we can also make it make it show we can also utilize a certain chemical we can also utilize chemical functionality to impart certain characteristics to a material. So, we can somehow impart some chemical functionality only to a specified region and not to the remaining region that might be required in certain cases because in case we want a dual functionality in one case we might require its attraction with something in another case we might its repulsion. So, we can from chemical functionality we can achieve duality or dual functionality from this particular arrangement. So, we can see we can see that we can achieve this chemical functionality. So, we can get either a deposition say this particular layer is good for deposition of one entity and not for the second entity. So, we can apply some sort of a resist. So, which will not allow any entity to grow on to it whereas, other portion will allow the growth of the secondary unit and this might be required for constructing say certain chips or certain electronic circuit. So, in that part this functionality will be very useful. So, in certain cases we want to build up structures which go in height. So, we might require deposition along certain areas and not along other areas and later on we can go upon making something else over it and then somehow joining them series or parallel or it can be any particular structure. So, this chemical functionality is very good because that will allow us to selectively deposit required materials. So, that is the advantage of controlling the chemical functionality or even controlling the wetting. So, it can allow us to achieve very low friction or to resist the deposition of water or any humidity on those surfaces of the electronic components when humidity is very high in the atmosphere. So, that is the advantage of this particular thing and depending on the space we can also somehow control the overall nature of this self assembly. So, if we have this tail group say tail group is like this and then we have a functional unit which is basically trying to form the network. So, we have something called spacer and then this is nothing but some sort of a joining or network or networker. So, assembly of this one will lead to so we can achieve certain structures. So, we can achieve certain structures if we the way we wanted to or we can also get some other sort of structures depending on the our networker if it requires a 6 fold, 4 fold and so on. So, we can get many different type of variety of this structures. So, the spacer width and height it will be very critical. So, that will decide what is the overall region which is available for us for deposition. So, in one case we can have some sort of a resist this one can be resist. So, now we have certain region which is available for deposition and in this case we can control the deposits. So, once we are depositing something we can achieve which is called a deposit which is getting deposited on to this particular available region and now this functionality. So, we have some sort of a resist and now we are getting deposit and this is now forming a structure within this particular pore. So, we are seeing that somehow we are we are able to this is a nothing but a network formation. So, we are forming some sort of a network. So, depending on that we can achieve very nice arrangement of we can achieve very nice network out here and it can be self self consistent or self self propagating. So, we can what we can get once we start another process it can allow deposition only along this particular region and because of its confined nature we can control the overall dia meter of this one and also the angularity can also be controlled depending on this our network functional group. So, depending on that it will provide the overall angle to it and the length will be decided by the spacer or the tail group. So, from that we can now achieve some sort of a network for which is required for the formation of nano structure. Now, depending on that we can also control the pore size if we control the overall the length of our spacer or the tail group we can also control how thin or how what will be the overall radius of that particular pore which can form. So, if you have a little longer space longer spacer we might get something like this but if we restrict our spacer we can also get pores which are much smaller. So, in this case we get very bigger pore in this case and then we can also get a smaller pore when we have a. So, we can keep our network are the same but in this case our the length of our spacer is this much but in this case our spacer length is only this much. So, accordingly we can somehow control how much is the spacer length and then what is the structure we get. So, in this in one case we can get structure which is more like this in the other case we will get something like this. At the same time if we somehow can control the overall geometry of our spacer then again we can control the pore structure. So, if you want to provide much more surface area to the pore we might require the pore to be very very tortuous. So, in that case we might require a different geometry of our spacer. So, spacer can be more like this. So, we can have a spacer which can be more like this. So, in that case what we will get in that case we will get more like this. Now, we can see now we have pore which is much more flowery kind. So, that is the part we can see. So, just by changing the geometry of our spacer we can somehow control. So, in this case if we had a hexagonal pore and very symmetric pore in this case we get more of a flowery type pore which can be obtained and again the thickness of the pore the diameter of this pore can be altered depending on the spacer geometry. So, we can see the networker is in the same in this case we can again change the networker. If we can make it square or something like that we can also attain structures which are like this. So, depending on our networker we can also change the porosity type and size. So, that is the overall combination of our spacer how the spacer has to be what is the geometry of the spacer and what is the how the networker will filter into the picture to give a resultant pore and to achieve a certain functionality or to in order to achieve that we enhance the surface the pore of the surface area of the pore in order to trap certain signals for it or to allow a growth of certain entity into it or to provide certain geometry or construction to the newly deposited structure into the pore the control of pore size is very essential and that can be controlled by playing around with the networker or the spacer. So, that is the one which makes this assembly much more useful to us again we can see in lotus effect is also controlled by the nano structure. So, we can see it can impart very high non wetting. So, wettability is one of the concern and that is governed by the microstructure. So, we can see if you have a lotus leaf if you have lotus leaf and you drop out droplet of water if it sits on to it it basically does not wet. So, we have the surface of the lotus leaf and then we have contact angles which are exceeding which are exceeding around 160, 165 degrees. So, that makes the surface super hydrophobic. So, in this case we have a structure we have the overall lotus leaf surface and a certain protrusions on the surface. If you see the cross section of it you will find there are certain micro protrusions which are sitting here and there. So, these are nothing but micro protrusions generally the lotus leaf the non wetting on lotus leaf is thought to be governed by the chemical composition or the apicuticular wax which is present on the lotus leaf surface. But it is apart from the non wetting nature of this apicuticular wax if had there been no roughness. So, the minimum surface energy of the surface will lead to a maximum contact angle of 120 degrees. So, maximum contact angle of only 120 degrees can be obtained with surface as the least surface energy. But in lotus leaf we are seeing contact angles in excess of 160 degrees. So, it means that chemistry of a surface is not enough on its own to govern the non wetting. So, there has to be some extra feature which is governing the overall non wetting to increase the contact angle from 120 to 160 degrees. So, this micro protrusions are the first regions which basically enhance the wetting angle and again contact angle and then again there are certain nano here which are present on the each of protrusions. So, each of protrusions will have certain nano here which is present on the surface. So, that in turn also increases the roughness by order of couple of times. And this roughness is the one which either increases the wetting or non wetting depending on the inherent nature of the surface. So, surface itself is non wetting the non wetting the degree of non wetting increases because of the micro roughness and then because of a nano roughness and vice versa as well. If the surface itself is hydrophilic in nature it is water attracting the contact angle will go down drastically by adding roughness to it. So, roughness will either enhance wetting when inherent surface itself is it is wet it is a wetting characteristic or it will also increase non wetting if the inherent surface is non wetting in nature. So, because of that we have the apparent contact angle is now increased because of our initial surface is apicutular wax that is hydrophilic in nature. So, macro protrusions enhance this contact angle to a high degree. So, it can go up to even up to like 140 degrees and from there 140 to 130 to 140 degrees. And then apparently the nano surface nano roughness enhances it further down to 160 degrees or higher than that. So, that is the overall role of nano structure which are present on the surface of lotus to impact non wetting to lotus leaf. And then certain classes of self assignment mono layers we have first we have Langmuir blogate films. These are formed basically by the weak or electrostatic forces or certain ionic forces ionic bonding between the surface and the film. They have energy to the order of 50 kilo joules per mole followed by thiols or they are also called self assignment mono layers. And they generally form covalent bonds and they have energy to the order of 150 to 200 kilo joules per mole. And then salinization which generally forms covalent bonds with silicon, silicon oxide or silicon carbide and it has energy to stability energy of around 300 to 450 kilo joules per mole. So, for Langmuir blogate we need to have a surface on which we have a tail group head group and then a tail group which is basically adhering on to it. But again this tail group should have concentration this can be again a liquid or it can be a substrate. Ideally the concentration of this particular entity the concentration of the film or the concentration of the secondary chemical should be much less than that of a missile concentration. So, concentration should be much less than missile concentration otherwise these all head groups will combine and they will form a missile of concentration is very high. They will go on to forming a missile structure. So, this will form a missile when the concentration of this particular chemical is much higher than the missile concentration. So, the concentration of this particular entity or the Langmuir blogate film to form a Langmuir blogate film the concentration of the chemical has to be much lesser than a missile concentration. So, that it can survive on the surface and get equally dispersed to form a very regular or a structured layer on to the substrate. Then again we have thiols. So, this is nothing but a sulphur bonding with the functional group or the and the hydrogen. It generally is a covalent bond with energy of 1500 to 200 kilo joules per mole and then third one we have salinization on silicon which is bonded with other 4 hydrogen atoms. So, hydrogen atoms can again be replaced by certain functional group later on. So, we can see examples of self-assembled monolayer. So, we have Langmuir blogate generally is very prominent on the alkyl acids such as RCOH. It is predominant on metal oxide Al 2 O 3 A G O or polar or ionic surfaces. Whereas thiols or self-assembly a self-assembly is dictated by thiols or phosphonates. It is it is a very high affinity for noble material such as gold, silver, copper and so on. Then third is the salinization. So, salinization is dominated by the silicon. So, it has either functional functional group or some hydrogen or halides which are available on the other side to complete its valency of 4. Utilize for the silica hydrated or other oxides it can it can form on silica hydrated or other oxides. So, we can see the three self-assignment monolayers. Langmuir blogate self-assembly which is nothing but thiols and then salinization which can occur. For the Langmuir blogate assembly first of all we need to have concentration which is much below that concentration of the missile. So, first thing is that we can first of all disperse this particular chemical. So, we have some sort of a barrier which will not allow the. So, we have this head and tail group which are dispersed on to a liquid and then we have some sort of a barrier or a Teflon barrier which will not allow this particles to come into it. So, once we start squeezing it through then these particular entities they will start coming closer and closer and then they have they will form like this. So, we can see that there are certain molecules which are either amphiphilic or hydrophilic. So, one entity will go on to this particular fluid media. So, we have a film which is forming and then we start compressing it and the compression of this one will decide what is the distance between the chains. We can also do secondary treatment we can also somehow compress it. Once we compress it we can form very dense layers and if you want to coat it on a certain entity. So, we can somehow take it something like this we can let this molecules come like this or and then we can put our substrate out here and then we start pulling it up. So, in the process if you start lifting it up then what we get is deposition of all these entities on the surface of this particular substrate or we can also make it go like this to finally deposited on to its surface and the process we can deposit them. So, we can see that we can deposit either the hydrophilic end or the hydrophobic end to the substrate this is nothing but substrate. So, now what we are getting we are getting very ordered film ordered films which are basically getting deposited on to that and these the overall the substrate can also the the porosity on this particular films can also be controlled. So, we can see that porosity or the distance between distance between chains can be controlled. Now, the control of porosity is very very critical in this particular aspect because that will decide what all chemicals or what all chemicals can be can permeate through this particular film. So, if you want to impact functionality that only hydrogen should be able to pass through or only oxygen should be able to pass through or only certain entities can pass through we can control the overall porosity of this Langmuir block at films. So, that can be dictated by compressing or by applying lower pressure lower lower compaction. So, that the so the all the chains are sparsely packed. So, in that case we can control the density of these particular amphiphilic or the hydrophilic entities all this change on a particular substrate. So, that that is that gives us a control that we can utilize this Langmuir block at assembly to somehow play with the play with the nature and the density of this particular film and impart particular permeability of porosity to do all these films. And again the stability of this one this particular chain is also dictated by the overall hydrogen either the hydrogen bonds or the van der Waals forces. So, the weak forces also dictate the stability of films. So, weak forces also dictate the stability of this film or the Langmuir block at assembly to provide much more crystallinity or stability or ordered nature to the films. And the second part can again of self assembly it can again be attained by this thiols. So, we can get functionalize alkanethiols on the gold surfaces. So, we can have a solution which is a thiol solution and this sulphur group has high affinity for the noble material such as gold, silver, copper and so on. And once we impart if we can make certain structure. So, we can electro deposit must put a deposit gold a certain pattern of gold. So, we have silicon layer and over that we can provide certain construction of gold assembly by the sputtering or any other technique. And then deposit this structure into a thiol solution. So, what we can get finally is a certain structure of gold which is now thiol attached to it with certain functional group. So, now eventually what we are getting we are getting a substrate which is nothing but our silicon. And then we have a very nicely layer structure of thiol layer. So, we can get a very good mono layer. So, we can get a self assembly of this particular structure or thiol on a silicon substrate which is again certain deposition of gold on the substrate. So, we can attain the self assembly by allowing the particular pattern deposition of gold on a silicon surface. And then once we deposit that particular surface of silicon which is now gold in a certain pattern that particular pattern zone of gold will now attract the thiol group. And thiol group with certain functionality to it any carbonaceous chain to it will now get attached to the gold particle to give a mono layer of that particular chain. So, in this particular case now we are getting a self assembly of this sulfur on this particular chain. And in salinization we are utilizing a particular functional group. So, we have a functional group of some R and that is combined with either hydrogen or ethanol. So, we have to satisfy its valency. So, where it is particular entity N this will be 4 minus that particular N and then what we are attaining silicon H x. So, essentially what is happening we have chain. So, we have a silicon group. So, we have R here R here and say x here and then we have OH and then we have certain functional group. So, in this case we are moving this function out here. So, what we are getting finally is a combination of silicon R oxygen and then R. So, essentially what we are getting we are getting a strong covalent bond. So, in this case that is what we are getting. So, we have a functional group of R functional group of R dash and then it combines with a third functional group of may be say R double dash. So, in that case we are getting we can get a certain very strong covalent bond of silicon with oxygen and then that can result a very strong attachment of this particular silicon surface. But the problem with silicon is that now it has 4 arms. So, it 1 arm has to go here, 2nd arm here, 3rd arm here, 4th arm here. So, we can get 4 order kind of entity out here. So, the overall problem here basically occurs that we can ideally we should get a structure which is more like this. So, we have substrate and then we should get 3 combination of silicon with say 1 oxygen, oxygen, oxygen with 3rd one should have some R dash sort of a chain. So, we can get this of a structure oxygen, oxygen, oxygen and then some sort of a R dash chain. But the problem with that can happen is that instead of combining with 1 oxygen out here it can break up that break up that chain and it instead of instead it can combine with R dash out here. So, it will lead to a chain which is in another direction and not in the top direction. So, we can see oxygen, oxygen it can have R on this side and then it can again have oxygen or R on this side. So, essentially we are getting a chain which is now not aligned to the other chains, but to some other two are different. So, we can have R dash silicon, oxygen, R dash, but there are certain other chains which are now going in different directions. So, this is not imparting a much density or alignment. So, the overall assemblage the self assembly is now not distorting the arrangement. So, it is not a self assembly because it is not assembling on its own. So, that can be problem associated with the silence. So, we can see that they have very strong bonding with the oxygen because of it because it is a covalent bond. So, it can give very strong alignment, very strong deposition of all this particular entities. So, we have oxygen, oxygen, oxygen and then we can have silicon which can combine with it and then it can impart R dash or some other entity which is which it can provide a very nice layer, but it can also lead to a problem of distorting the overall geometry and then fracturing the overall concept of self assembly in this particular case. So, in comparison we can see Langmuir blockage films, they are they can be porous. So, we can also control the porosity depending on the structure of kind of pressure or the kind of pressure or the kind of structure we use. Whereas, thiols they have a very strong affinity for sulfur for noble material. So, sulfur has a very high affinity for noble metals. So, we can let deposit on a gold, copper or silver surfaces by spread deposition and then we can control where the thiol has to come. Whereas, silence they tend to be highly explosive or toxic reducing agents. So, because they have a very high amount of hydrogen as well and the bond is also very, very strong. So, in that in that particular process once the bond breaks it can release very high energy and make the thing explosive or toxic. The application of Langmuir blockage films applies in metal insulator, metal insulator semi conductors, biological membranes of a drug delivery, chemistry of changing the chemistry of biologically active molecules and even the modeling of the biological systems. Whereas, thiols they are easy to pattern via certain techniques such as lithography. They can be highly useful for the nano electromechanical systems because it can also withstand very harsh chemical cleaning treatments. So, that is advantage with the thiols that you can utilize them in the micro electromechanical systems and it can also reduce the overall wear or the harsh chemical environment that is that can predominate in such structures in the moving parts. Silence they can adhere to glass fibers. So, again it can also be utilized for water repellent coatings. It can also initiate combustion in the compressed air stream. It can also be utilized for deposition of amorphous silicon on glass to stabilize the overall composite materials. So, there are certain applicability of this silent films as well, but they tend to be very explosive or toxic as well. So, that again it requires a better control, but these films they have very higher bond energy and they can be very stable as well. In certain pattern we can also somehow construct a selective hydrophobic and hydrophilic surfaces. So, if you select a particular entity and let us deposit gold on to that and then if we can somehow control that we want to deposit only hydrophobic surfaces and then we can quote it again and then we can deposit a patent surface again to deposit something else may be say hydrophilic surfaces only on other regions. So, we have phobic regions. So, we can have CH 3 bond here whereas, we have OH bond. So, this is hydrophobic whereas, these surfaces are hydrophilic. So, in case when we want to impart a dual functionality to a material we want certain regions to be hydrophobic and other regions to be hydrophilic we can impart that particular functionality. So, we can have certain regions which are hydrophilic and hydrophobic. So, we can have certain regions. So, now this particular material can be tailored accordingly that either we can want to capture hydrophobic or hydrophilicity. Hydrophobic nature might be required. So, that there is no contact of water on the surface whereas, hydrophilic can be required to impart certain lubrication layer. So, that they do not undergo corrosion to that extent or do not undergo wear to that extent. So, we might require hydrophobicity or hydrophilicity on the same plate form. So, if a substrate requires both these functionalities we can somehow tailor them and impart both of these features. So, if a particular material say if a water droplet falls on this particular substrate it will stick because it has a localized hydrophilic regions. At the same time if oil spills on it will still try to stick it because again you have certain amphiphilic regions which are available on the particular patterned surface. So, we can achieve dual functionality or duality in a particular surface or if you want to control it vice versa we can also eliminate that particular part by controlling the hydrophobicity or amphiphobicity on the patterned surface. Again, self-assembled monoliths can be produced either by the physical vapor deposition, electro deposition or even by electro less deposition there are many other techniques as well. The kinetics is basically dictated that all these chains come to the surface very quickly, but the time it requires for organization. So, we can see it as a fast step of adsorption, thickness can be achieved in a few minutes, but it is the rate deciding step is nothing but the organization of these particular chains because they take time in terms of corresponding in terms of basically acting towards the surface forces which are acting around. These are first of all the ionic or the forces with the substrate and second thing is the weak or the secondary bonding with the nearby chains. So, that is the that is what which requires very high time. Temperature if you increase the temperature it will try to basically form the coating or the layer at much rapid rate, but it will have many effects. So, if we deposit them at room temperature it will improve the kinetics and reduce the defects. So, it will make it very crystalline concentration of adsorbate in the solution if you have low concentration it will it might require longer immersion time, but it will result high crystallinity. So, that is coherent with the lower temperature again the substrate is adsorbate is very pure then the overall properties physical properties of the same can be much better or much more predictable. So, that can also lead to the conformation of coating to a certain requirement dirt or contamination of surface on the substrate can also cause certain defects. So, we can see the kinetics is basically being dictated by the rate in which the chains are getting organized and there is certain temperature or pressure parameters. So, if you have higher temperature it might lead to formation very rapidly, but then it will require it will it can create much more surface defects. So, lower temperature preparation can make it much more crystalline in nature the kinetics basically will be comparable much though much lower, but it will have very less lesser defects and lower concentration can again impart higher crystallinity, because now they can they will have enough time the overall deposition and then organization will be much more quicker than once another entity is notice. So, they can have enough time, because they are localization of these particular chains is much further from each other. So, they tend to become much more crystalline, because they have now enough time available before a next entity is coming closer to them again high purity is also very much required. So, we can predict what is the overall functionality that we can impart to the surface and again we can have selective assembly we can make it either highly hydrophobic or hydrophilic in nature. So, we can have certain selective assembly. So, we can have organization of different parts on a component. So, we can organize different zones in a particular component. So, it is again nothing but the extension of certain functionality. So, we can see that we can attain self assembly. So, if we start developing certain thioles and then start giving out functional chains of say maybe methyl say on a gold substrate if we can impart again thioles and then to make it hydro hydrophobic in nature and then again we can somehow try to we can impart it in assembly secondary level of assembly to this particular methyl group and if we can polymerize a lubricant on to it. So, now what we can make we can make now a layer which can take care of the friction and the remaining areas we can try to make it hydrophobic. So, we have assembly self assembly of lubrication and then this one will be impart as hydrophobicity. So, in this case we are achieving lubrication. So, it will do nothing but it will reduce the friction of the moving parts and this hydrophobicity will not allow any no sticking of water droplets. So, we can achieve multiple functionality or we can achieve a selective assembly of combining the various concepts of achieving more than one type of functionality to a particular component. So, a particular component has to be utilized in a wear condition where we have even water. So, we want to impart lubrication to it by polymerizing a particular polymeric chain of functional chain and then we can also impart non wetting to the surface by applying a layer. So, in that case we are able to achieve non lower friction as well as super hydrophobicity or hydrophobicity on the same component that is nothing but the selective assembly by utilizing that we can achieve dual functionality. Then the assembly can also be stochastic in nature which means it is difficult to predict. So, if you take a particular mica surface and then we put a water droplet and then we disperse some glass nanospheres. So, we have many glass spheres which are basically now which are there in a on a particular fluid on a water droplet. So, we have water droplet, we have a mica surface and we depositing certain nanospheres of glass. So, essentially once this particular water droplet starts evaporating then we can see that these micro spheres of silica they will start forming a structure on the on the mica surface. So, these are nothing but your glass spheres this is water droplet and this is your mica surface. So, essentially what you will see you will see a very nice organization of these particular particles of the spheres if you zoom it up out here it will look like this. So, we have very nice organization of all these spheres on this particular particle it means that because of surface tension between the particles because we are at some fluid layer or water layer on the on the glass surface or the glass all glass spheres. So, as soon as the water is now evaporating because of the capillarity action all these nanospheres come in contact and they form certain organized layer, but this is very difficult to predict which type of how it will basically develop because it has a similar probability in all the directions, but it will form a very nice dense organized layer that is called micro assembly. And since it is difficult to predict it is called stochastic micro assembly again there can be slight irregularities can be basically they can come into picture, but that will arise because of the non uniformity of the spherical particles or the spheres because if there is some non uniformity on the surface of the spheres it will again lead to certain distortion. So, once sphere has a bad surface it might lead to a it might lead to a different orientation of the particles now. So, instead of coming like this it might go something. So, if one particle is bad say one of the particles is bad it will basically destroy the entire micro assembly again application of SEMs they can go from changing the surface properties of the electrodes. So, we can enhance the properties of the electrodes we can enhance certain electronic properties we can also utilize them in MEMS and MEMS there is nano electromechanical systems of micro electronic mechanical systems can be utilized for controlling the electron transfer. So, by changing the functionality of the surface chain it can protect metals from harsh chemicals and Hs like in thiols it can reduce sticking of MEMS and MEMS in humidity environments it can alter the properties of glass it can create either hydrophobic or hydrophilic mono layers it can also be utilized for on the car windshields for keeping them clear of rain. So, these are the various applications of SEM we can take them from chemistry to electronics to even hydrophobic entities or even biological units where we can impart certain porosity or drug livery using this particular mono layer. So, we can see that the overall application is not limited to any one entity but it can go from myriad applications. So, in summary we had Langmuir blogger films which are nothing but the lower interaction the lower forces interactions such as ionic or co or hydrogen bonds, van der Waal forces then we also saw that thiols have very high affinity for precious metals. So, they tend to form a self assembly, salinization they have very high energy of the bonding. So, they can be very toxic or explosives if it is so, but they can form very strong layers, but the only problem with them is if they undergo breakage of bond in any other direction it can lead to a non assembly or so. Then we also learned about the stochastic assembly in this case we cannot predict how the assembly will occur, but again it is self sustaining and construct to a very regular structure. So, with this I will end my lecture. Thank you.