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Module 1: Synthesis of Nanomaterials

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Video 1: Sol-Gel and Micro Emulsion Techniques
Welcome back to the lecture series and application of a nanotechnology in agriculture.So, at this stage of the course we are talking about the basics of nanotechnology and inthat context, we have talked about the classification of nanomaterial based on their size, geometry,shape and based on their origin or chemical origin, post that we have talked about thedifferent methods of synthesis broadly the outline of physical methods, chemical methodsand the biological methods.And within that we have talked little bit in depth about the physical methods.So, if you recollect this is what we have already talked about the physical, chemicaland biological methods.And within that we talked about the 5 different techniques high energy ball milling, pulsevapor deposition, laser pyrolysis, flash spray pyrolysis, electro-spraying, melt mixing andpolymer composite development.And basic idea what we have discussed in the physical methods of synthesis is that hereyou having a bulk material which I am now shading in red.This bulk material is exposed to different physical forces like lasers, mechanical forces,heat, light and all sorts of different forces very high temperature.And inside a vacuum chamber the material gets abraded, the abrasion takes place and thatleads to either the deposition or formation of a smaller size particles.And this is essentially a top down approach, so now our goal will be to explore the secondlevel of synthesis which is the chemical level of synthesis.So, here we will be discussing about SOL-gel, micro emulsion technique, hydrothermal synthesis,polyol synthesis, chemical vapor synthesis and plasma enhanced chemical vapor synthesis.So, let us start with a SOL-gel synthesis which is pretty straight forward techniqueSOL gel synthesis under the umbrella of chemical synthesis of nanomaterials.So, in the SOL-gel synthesis what we do there are 2 types of components a SOL which is acolloidal suspension of solid particle in a liquid.So basically, you have a SOL here which is you are having this colloidal particle allover the place in a liquid suspension.And what you are having is a gel which is a polymer containing liquid.So, you have, so this is your gel which is polymer containing liquid.And you are having colloidal particles in liquid, so thus this process includes thecreation of salts in a liquid that led to the formation of network of discrete particlesor network polymer by the connection of SOL particles.So essentially what you are doing is that actually I pick up a different color out here,let me kind of modify this colors that will these are the polymer particles shown in green.So, the idea is for mixing them what you are getting is these are the polymer particles.So, polymer particles are getting partly aggregated and you have different techniques to separatethem out by sonication or other techniques and on top of that the colloidal salts aregetting adhered something like this.These are the polymeric matrix and within the polymeric matrix you are having the nanoparticleswhich are shown in red.So, in other word this process includes creation of SOL in the liquid that lead to the formationof network of discrete particles.So, this is the network of discrete particles or network polymer by the connection of SOLparticle, hydrolysis and condensation at typical steps of SOL-gel process in which the formaluser’s water to disintegrate the bonds of the precursor that is also the first stepin the formation of the gel phase.This process is then followed by condensation that leads to the formation of nanomaterialsafter which excess water is removed to determine the final structure of the material.So basically, condensation evaporation basic techniques hydrolysis and condensation andevaporation.These are the typical processes which are being used in the SOL-gel synthesis.So, this is the basic SOL-gel synthesis what you needed to understand.So, the next technique from here we will be moving is and this section is micro-emulsiontechnique.So, micro-emulsion can be defined as thermally stable macroscopically homogeneous opticallytransparent and isotopic dispersions constituting minimum of 3 components.So, what are the 3 component micro-emulsion techniques have, so it has a polar phase whichis generally water, polar phase is mostly water.And even non-polar phase generally hydrocarbon liquid or oil you have a non-polar phase whichis mostly liquid hydrocarbon or oil.And you have a surfactant, the third thing is a surfactant and we have already discussedabout surfactants in the physical synthesis if you just recollect where we talked aboutsurfactants.Here we talked about with surfactants, so these are the surfactants it could be an anionicsurfactant, it could be a cationic surfactant, it could be a non-ionic surfactant which arekind of helping in not promoting aggregation reducing the surface energy and reducing thesize.There are 3 things what a surfactant does and here also the same principles of surfactantswill apply the surfactant which will ensure that.So, say for example you have no you have to understand micro emulsion is something likethis say for example you have this polar phase which is water.And in that you have oil phase which I am showing inwhich is immiscible in water.This is the non-polar phase, this is the polar phase which is water.Then you have a surfactant which I am representing with say green color which is this.And now you wanted to synthesis a particle says for example some particular particleyou wanted to synthesis.And that material is in colloidal suspension like out here which is red.So, you wanted to create a nanostructure of these ones which isnanomaterial to be synthesized.Now say for example you take this whole mix and you sonicated or you give some kind offorces by which they are it will create an agitation out here, some form of an agitationwhich is happening either by you know say sonication or shaking or somewhere other,you creating an agitating the molecules.So, what will happen is these non-polar phases these ones, they will try to self assemble,so something like this will rise out of it.These non-polar moieties within the liquid, so this is the polar phase which is waterwithin water these non-polar moieties will form some kind of a spherical in order toreduce their surface energy.And within that you have these surfactants which will ensure they remain separated fromeach other and since during agitation randomly some ofthe particles will get trap inside.So, in other word each one of this is sphere what you are observing out here is actingas a nano reactant nano vessel.Now at this is stage if you evaporate the water out or lyophilize or do something toget rid of the polar phase.So, what you are left with is this, so your water is gone, water removed, what you areleft with is something like this.And you can control the size by what kind of force, what kind of temperature you areallowing this reaction to occur and some of the polar moieties may get trap or may notget trap depending on what level of evaporation or lyophilization you are doing.So, this is the second technique which is a fairly low temperature technique mostlyand pretty commonly used and pretty popular among the people who work in the area.So, surfactant molecule thus creates the interfacial layer separating the aqueous and the organicphases, reducing the interfacial tension.So, this is what the surfactants is doing, so out here it is reducing the interfacialtension creates the interfacial layers separating the aqueous and the organic phase reduce theinterfacial tension between the micro-emulsions.And the excess phase act as a steric barrier preventing the collisions of the droplets.So, it also prevents these droplets you know to collides together, micro-emulsion systemconsists of mono-disperse is spherical droplets of the diameter ranging from 800 to 8000 nanometerof oil in water or oil or water in oil depending on the surfactant use.And with water in oil reverse micellar system act as an excellent reaction type for nanomaterialssynthesis.And reverse micellar is water in oil micro-emulsion where polar head groups of the surfactantscreating the aqueous score and resides towards inside where as the organic tail of the surfactantmolecule directed outside.So, you could have a reverse micell, you could have normal depending on a whether it is itwater in oil or oil in water.In general, there are 2 micro-emulsion roots to synthesis nano material synthesis.One is micro-emulsion method and two is basically water in oil and or oil in water as I havemention earlier.These are some of the very I should say non-energy intensive processes if you compare a micro-emulsionwith respect to any of the physical methods what we have already discuss earlier.So, you can understand that these kind of techniques does not require heavy machineryor high energy.And yet they are very user-friendly techniques for most of the labs who work on nanomaterials,from here we move onto the next synthesis which is our we are moving onto the hydrothermalsynthesis.

Video 2: Hydrothermal and Chemical Vapour Synthesis
So, hydrothermal synthesis if we look at the methods used for the fabricate of nanomaterialmetal oxides mostly it is used for.Now we are into hydrothermal synthesis, so hydrothermal synthesis used fabricate nanomaterialmetal oxide, iron oxide or lithium iron phosphate keeping control over the characteristics ofthe particle by varying the properties of near or super critical water by using differentpressure and temperature condition as its says.So, they are is this parameter pressure, so depending on what kind of pressure you aregiving a what kind of temperature thermal and pressure.These 2 parameters in the presence of how much water you are keeping into the systemnear or super critical water by using different pressure and temperature.So, 3 parameters water, pressure and temperature, this is the interaction of these 3 which dictatesthe hydrothermal synthesis.But this is again a high energy system, hydrothermal synthesis requires pretty high energy.So, it can be performed in 2 types of system.A batch hydrothermal or continuous hydrothermal process the formal is able to carry out asystem with desired ratio phases while the latter allows a higher rate of reaction tobe achieved at a shorter period of time.So, this is another technique which is pretty commonly used in different polymers and differentmetal oxides.Next, we will move on to polyol synthesis.So, what is polyol synthesis, polyol synthesis is basically the synthesis of metal containingcompounds using poly ethylene glycol PEG, use of poly ethylene glycol.So, use of PEG as a reaction medium that play a role of solvent reducing agent complexingagent at the same time.So, the role of PEG is as reducing agent, complexing agent, at the same time it is actingas a reaction medium and plays as a basic solvent.So, it has multiple role to play in the polyol synthesis.This chemical process was used to synthesis wide range of metal-based nanomaterials oflike silver, platinum, palladium, copper several metal oxides like zinc oxide indium tin oxide,gadolinium oxide different magnetic nanomaterials so and so forth.So, as we will move through you realize poly ethylene glycol is used for several deliverysystems apart from being used for different kind of metal or metal oxides metal oxidesystem.So, we will later into that one through will be using, so here you should have an ideathat what we synthesis are these terminologies really mean to you.But when we will come to the real synthesis or real application we will talk about forthese particles.We can use these kinds of synthesis for this particular particle or this kind of a nanomaterial,we can use this kind of synthesis.So now from polyol synthesis we move onto the next one which is chemical vapor depositionor chemical vapor synthesis which is again on the same line as physical synthesis.So, chemical vapor deposition CVD and chemical vapor synthesisCVD or CVS is a process which is often use for deposition of solid firm from the vaporphase.So, you have something in the vapor phase as we mention in the physical synthesis somethingin the vapor phase that you are depositing it on a substrate.It is kind of used for all sorts of thin film deposition on a substrate most likely we usefor thin films synthesis.So thin films produce by CVD processes at certain conditions also contain ultra fineparticle.Hence the synthesis of nanomaterial can also be possible by this method.If CVD system is modified, say for example you have high temperature in auto reactor,high super saturation or low residence time on a small substrate.If you have all these parameters and you will really be wanted to use very small amountto synthesize nanomaterial on a substrate.Then the best idea is to follows CVD, but the problem with CVD is the very moment youmove to CVD, CVD demands a lot of an intensive instrumentation and high-pressure requirements,vacuum requirements and several other complex technical knowhows is essential for chemicalvapor deposition.So, from CVD, so we are into chemical vapor deposition and plasma enhanced chemical vapordeposition which is a last one.Plasma enhanced chemical vapor deposition is pretty much further modification of thiswhich is plasma enhanced chemical vapor deposition.So, basically plasma enhanced chemical vapor deposition also called plasma assisted chemicalvapor deposition is a popular CVD process which is chemical vapor deposition processwhich is widely used for the deposition of thin films.And plasma enhanced chemical vapor deposition process can also be used for synthesis nanomaterial,as the name suggest the plasma enhances the chemical reactions.So, you are using plasma as that force just we are talking about the physical forces whichis enhancing basically plasma enhancing the nanomaterial giving sufficient energy enhancesthe chemical reaction for the synthesis of thin films and nanomaterial.So, when we talk about such processes as I was mentioning earlier you will be needinga vacuum processing unit.So, these are those requirements or vacuum unit you will be needing.Then you will be needing a very high-power supply, you need a gaseous precursor, so inother word you need pretty decently high-power supply.And you need pretty specialized apparatus you have this plasma enhanced technical vapordeposition to take place.So, you realize that these processes which are as of now we have discussed the chemicaland the physical process is.They are the one which help in initiating the field, but now slowly we are realizingmuch of these techniques require extremely high energy.And needs very very specialized training in the contrary if you try to emulate naturethe way biology has done things.We may be able to make a very different industrial development or very different kind of industryfor nanoparticle or nanomaterial synthesis by using biological rule.So, that will be our next target while we will be winding up the basic nanotechnologysection.And from the biological routes we will move onto the application part which will be mucheasier to you know slowly bringing down the energy of synthesis and then moving into theagriculture domain.So, I will close in here, so our next target will be understanding the biological routeof nanomaterial synthesis which in the current context of sustainability, sustainable developmentis much more relevant to us in terms of delivery of agro chemicals, release of agro chemicalsin the agriculture sector.And as well as boosting the economy of small-scale industries which can achieve these thingswho do not have such sophisticated instrumentation as well as very high infrastructure.So, with this I will conclude and in our next class we will move onto the biological synthesisof nanomaterials the future, the sustainable future thank you.