noc18-bt25-Lecture 9-Physical Approaches to Nanomaterial Synthesis

[Music] [Music] welcome back to the course on nanotechnology applications in agriculture so in this module exclusively we will be talking about the nanomaterial synthesis nanomaterial classification and the characterization tools which are being employed so as you have already aware in the previous class we talked about the classification of nanomaterials and and that just to have a brief recap what we talked about we talked about the shape and geometry based on which in the nanoparticles are being classified we talked about the chemical nature based on which they are being classified and we talked about nanocages nano crystals nano belts nano fiber nanoparticles nano tubes nano wares quantum dots and nano composites and I give exclusive examples highlighting how each one of these could be helpful and one thing which I must out and many of these structures are exceptionally helpful in developing next generation of biosensors for agricultural applications because when we talk about precision farming where we are talking about based on the soil assay how precisely we have to apply the fertilizer in order to ensure a sustainable growth of the ecosystem then we need to test we need to have a small sensors or micro sensors which could be used or utilized to detect the different contaminants in the soil so one of the areas where tremendous amount of a stress has been put in precision farming is developing nano based sensors for agricultural applications so the next classification route what he have discussed was the chemical nature where we talked about the organic inorganic and carbon-based and in the organic we talked about dendrimers micelles liposomes carotene and most of them are biodegradable and non-toxic and most of them have hollow cores and they could be used as nano capsules to delivery any kind of active ingredient or any kind of agro chemicals at a specific site not only that much of these organic nano capsules could be tailor-made to open up or closed according to the electromagnetic radiation or any other form of radiation like heat or some other source of energy okay similarly in the same line we have the inorganic nanomaterials we are mostly aluminium cadmium cobalt copper silver gold iron zinc lead so most of these metal based are also used to deliver different forms of pesticides or they could even at times could replace the pesticide in order to reduce the requirements of pesticides so we have talked about these different forms of inorganic ones we talked about the metal sulphide rare earth and metal oxide based ones and then we talked about the carbon-based one where we highlighted about fullerenes graphene's carbon nanotubes carbon nanofibers carbon dots activated carbon nano diamonds and all this kind of other structures so today what we will do will pick up this part where we talk about broadly about the synthesis of nano material let's start the synthesis of nanomaterials in terms of the synthesis when you talk about there are three broad classification of synthesis either it will be a physical synthesis or it will be a chemical synthesis or it will be a biological synthesis now there may be time where we may be using two different techniques maybe we will be using physical and chemical physical chemical method of synthesis or chemical biological methods of synthesis or biophysical methods of synthesis so or maybe we may use all the three physico-chemical bio logical route of synthesis as more and more and technology's advancing these watertight compartments of synthesis of nano material is slowly kind of you know the gap or the clear-cut demarcation is slowly getting removed they are almost now emerging but what is interesting to note here is that all these synthesis falls under two different approach whether it is a top-down approach or it is a bottom-up approach okay so when we talk about a top-down approach so basic classification they could be classified into two groups start different methods synthesis nanomaterials okay so either it will be a top-down approach or it will be a bottom-up approach when you talk about a top-down approach so essentially what we are talking about is we take bulk material something like this this is a bulk material which is filled with atoms which are constituting this bulk material now this bulk material has exposed surface area like this this is the exposed surface area you could see now what we do is we take this bulk material and we break it down into say powder what we are getting is something like this they could be uniform or you can categorize them they can you can you know fine-tune them you can filter them something like this depending on how precise or how precision filters you're having and based on that something like this okay so depending on how finer you go you decide the size of the narrow material say for example if each one of these circle represents a single atom then we are talking about a single atom out here you're talking about two atoms we are talking about three atoms you can for like five okay so now if you look at it the amount of surface which are available is for that particular volume is this much so if you realize as you are increasing the number of atoms your per unit surface to volume ratio is decreasing and if you are reducing the number of atoms your per unit surface to volume ratio is increasing so the reactivity of so if you look at it as we go down with the size the reactivity is increasing in this order and the exposed surface area out here on the other side is decreasing like this so which is surface-to-volume okay where is out here it is the reactivity which is increasing so this is a top-down approach where you take a bulk material and grind it by different techniques and bring it to the atomic resolution whereas on the other hand if you follow a bottom-up approach what you do here is you are already having small moieties like this into the form of salts in the form of gels and whatsoever now using so you're having the atoms and the molecules at your disposal you either some form of self-assembly either it may be template based or natural self-assembly or template based self-assembly or chemical self-assembly there are multiple roots what you can follow here by virtue of which you are creating specific structures say you create structure like this what he talked about nano ribbons okay or you create a structure like this what we talked about cubes like wrap ribbon like structure you can create particles like this you can have different kind of dimension different kind of shapes like this okay so this is the other approach we're from a small competence you can confine them so the way you do it is you can find these particles you are allowing them to react while they are reacting you add some kind of agents in between which will give them something some kind of a capping agent what we call about which will give them some form of assistance to self-assemble in a certain way so depending on the type of capping agent which is used in a very small concentration as compared to the amount of nanoparticles there isn't a very very small concentration but they help to separate out the particles in a way that suppose it is there so once you introduce the capping agent out here they will help to separate out these particles in a certain way and it may be possible you may receive something like this something like this depending on what kind of capping agent you are using and as a matter of fact based on the capping agent in a synthesis where all the parameters are kept constant just by addition of different kind of capping agent you can vary the geometry of the particle very extensively fairly extensively you can change the whole geometry of the particle because the capping agent is just like not only it separates out the atom it creates a finite distance between the atoms and it creates a certain kind of unique bond dynamics between the atoms so this is essentially a bottom-up approach of synthesis of nanoparticles so where if you reach here which is or here same way or you reach like this out here reach out here so these are the two broad ways and under these two broad ways the top-down and bottom-up approach what you are having are the broad classification nanoparticle synthesis which is your physical methods chemical methods and biological methods so when you talk about physical methods so what we are essentially talking about is we are creating mechanical pressure or high-energy radiation or thermal energy or electrical energy these are the different routes we are following or did these are the different forces which are employing and what they essentially do these different forces they causes material abrasion one aspect they may cause melting in reparation because of these physical forces or they may even cause condensation and this is how we generate nano structures so what you are getting is and this physical technique is mostly I won't say completely but mostly employed for if you look back to the previous slide we talked about mostly employed for top-down approach but that's not the complete fact there may be a situation they could be used at these physical forces could be used for this kind of self-assembly process also the assistant self-assembly but mostly if you look at it the kind of physical forces we are talking about here are mechanical pressure high-energy radiation thermal energy electrical energy all could be used for both so all these forces so in other word when the physical forces are used for bottom-up approach in that case that will cause these may cause in that situation self-assembly also when we are talking about bottom-up approach self-assembly leading to the formation of nano structure so this is where we are talking about bottom-up approach and this is where we are talking about these kind of things happen in top-down approach okay so now what are the different physical tools which are so this is how the process works either there will be a mechanical pressure there will be high-energy radiation or there will be thermal energy or there electric energy or even even this could use magnetic field okay it is possible that you can use magnetic field or the part of energy could be utilized to either self-assemble or bringing about some of these top-down approaches okay now what are the different physical techniques so this is the whole basis how it happens now let's talk about the techniques physical techniques which are available so one of the technique major technique is high energy ball milling okay high energy ball milling so when you talk about Hydra ball milling just basically say for example suppose you have two balls like this and they are moving at in different directions okay so this is where you are allowing your material you know to grind you can control the speed of this so this is a material something like this you can control the speed of these spheres you can control the size you can control the contact area between them so you can do a lot of manipulation but this is something like an high energy ball milling we'll talk later about the pictures of this how really work let's enumerate at this time what are the different techniques which are being used okay next in the line is pulse vapor deposition we'll talk later about the detail of this technique okay pulse by vapor deposition the one point you will realize in most of these physical techniques they are pretty constants in intensive technique the third one is laser pyrolysis your PI realizing something using laser energy then you have flash spray pyrolysis followed by electro spring then you have melt mixing so at this point we are just enumerated all the different techniques which are available for physical mode of generating nanomaterials and then we will talk individually about these techniques what they signify and how these could be used and what are the cost involved in it and what are the different kind of nanomaterials which may require this kind of pretty aggressive and very cost intensive techniques and all of them are fairly cost intensive techniques [Music] [Music]