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Module 1: Overview of Nanotechnology

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Welcome you all to the course in Application of Nanotechnology in agriculture.So we have introduced the basics of agriculture, the use of different kind of chemicals inthe form of pesticides, herbicides, fertilizers in the modern day agriculture.So this module will concern with current state of art or state of art of nanotechnology wherewe will be dealing with the classification of nanomaterials we will be dealing with thedifferent kind or the broad classification of synthesis techniques which are being used.The third aspect what we will be dealing out here will be the different characterizationtools which have been employed in characterizing the nanomaterials, in understanding theirphysical, chemical properties and their surface properties.So this whole fragment or this whole module is a kind of a walkthrough with differenttechnologies of nanoscience.So if we see nanotechnology.So it goes back to one of the famous quotes from Richard Feynman he says there is a lotof room at the bottom, what that essentially means is that as you really go down in termsof size if you recollect in the very first module where I give you an explanation ofhow the nano structure they look it, if you have a bulk structure and you break it downto smaller and smaller and smaller pieces.Your expose surface area is to volume ratio is really going to go half, and that exactlywhere lies the catch that you have lot more surface for reactivity, so in other word inthe nano domain the reactivity of material is exceptionally high.So in that context Feynman quoted that there is plenty of room at the bottom and with theonset of modern day nanomaterial synthesis we realise there are 2 broad approaches whatcan be dealt.The one of the approach is top down approach, the other one is the bottom up approach andmost of the synthesis techniques are classified under these 2 heads which is top down or bottomup.So we did talk about top down approach we are essentially talking about taking a bulkmaterial.Say for example all of you must have seen where wheat is being grounded to make theflour.So what is wheat is wheat is a bulk material.So what you are doing you are putting in a mill could be a ball mill or any other kindof mill or it could be a grinder like this.So you are bringing down the size of the constituent by grinding it.In other another word you are putting mechanical pressure, we are quite putting gigantic amountof pressure to make it powdery or depending on what level of grain size you can make itcoarse, you can make it fine, you can make it very fine, now this could also been achievedwith other material by putting thermal energy, by putting other form of energies.So that basically you are breaking up big stuff a bulk material into smaller size whichis top down approach, whereas bottom up of approach is where you are taking small atoms,it’s tough to say small atoms rather I would say some kind of a salt, you should be somekind of a salt and you are self assembling them in a reaction vessel to form smallerparticles by the simple process of self assembly or directed assembly or template driven assembly.All sorts of technique which lead to assembling or clustering or quisling of handful of atomsin a certain geometry or maybe in a dynamic geometry, we talk about these what you meantby certain geometry or in a dynamic geometry.In a dynamic symmetry they are changing their shape confirmation or the arrangement of theparticle depending on their state of existence.So these are the broad, broad ways how we can look as a layman how we can make nanostructure.So, to formally start of it so this module we will be dealing withnanotechnology and whether nanotechnology will be dealing with classification of nanomaterials,then synthesis of nanomaterialsand the third section we will be dealing with characterization of nanomaterials.Now in terms of classification of nanomaterials, these could be classified into 2 groups basedon their shape or geometry and secondly based on their chemical nature,if we classify them based on their shape and geometry they could be classified underthey could be either called as nano cages.So these nano cages first code in 2002 discard kind of nanomaterials is halo interior andporous wall container metallic nano particle in size, their size ranges from 10 to 100nanometre, it is something like think of a cube and inside it you are having the nanoparticlesitting.So in other word what you have done is essentially something like this we have entrap the moleculesinside it and mostly it has as I mention this class of nanomaterials is halo interior itis hallow.And it has porous walls, pretty porous wall and containing metallic mostly metallic nanoparticlesare present in them and their size range varies from 100 to 150 nanometre.So, then come the next one which is nano crystal, these are of different shapes of crystalsit could be the easiest to draw with cubic crystals something like this, cubic shapethe basic crystalline structure and they are approximately 100 nanometres.Then comes nano belt these are ribbon like structuressomething like this, nano belt is thin and flat sheet of ribbon like structures.They are typically 30 to 300 nanometre depending on at what size you wanted to pitch your nanomaterialsfor your specific purpose and nano belts with rectangular cross section and well definedcrystalline facets, enable it to attain unique optical confinement they have very interestingoptical confinements.And it is micro cavities and it could use for the catalysis and it has lot of piezoelectricproperties, think of it because we can compress them, so that gives it tremendous scope ofpiezoelectric features, it could be pretty extensively for catalysis and it has lot ofthese micro cavities.Next is the nano fibers, fourth one is nanofiber.The nanofiber is a nano fibrous mesh or a network like this.Something like this and it is a 2D mostly it is a 2D mesh and having a diameter lessthan around 100 nanometres.So each one of this having pretty small diameter and these could be used for different kindof biomedical application as well as for fertilizers release as well as several other release ofactive compounds so essentially what you are doing, you are wrapping the particles likethis in this nano fibre mesh.Next, we have nanoparticles the name itself says these are simple particles of differentshape they could have geometry like this, they could have a flower geometry like this,all sorts of geometry you will observe in them.So these are the nanoparticles and there is where you can really go down with the size,you can really go down to 1 nanometre easily in these kind of particles.Because you are not restricted by any kind of spreading out in these stuff, so then youhave nano tubes.So the nano tubes as the name itself indicates so nanoparticles are the one which typicallycan be reduced to 1 nanometre or maybe even less than that.That is where you have lot of room to reduce the size.Next is the nano tube, as the tube says so these are something like a cylindrical structurelike this.As a microscopic tube with the diameter which is measured in nanometre less than 100 nanometreand nano tubes are mostly hollow so this whole part is empty, so we can fill stuff into this,on the contrary nano rod if you talk about it is a solid structure.So you could have tubes in 2 ways like either like this which is solid, nano rod whereaswhen you talk about the tube it is the hollow cavity moving through.Then we talk about nano wires which is similar to ribbons though again there are differentnomenclature introduced by different people in the pretty early phases of nanotechnology.So nano wire is a smart 1 dimension nano structural material with a dimension of 10 to the power-9 meters, then comes quantum dots.So quantum dots is which is represented QD (quantum dots).So quantum-dot is a nano crystal of semiconducting material small enough to exhibit quantum mechanicalproperties and their excitons are confined in all the 3 dimension, these exhibit strongsize dependent optical and electronic properties and quantum dot can contain few as 100 to100,000 atoms within a quantum dot volume with a diameter of 10 to 50 atoms, when wetalk about quantum dot we are talking about 10 to 15 atoms.And they have very very interesting semiconducting properties, electrical properties and theyhave tremendous potential but you control their size is a real challenge.So it is not really easy to handle anything between 10 to 50 atoms and uniformly obtaining10 to 50 atoms over a period of time.So quantum dot on one hand is a very promising stuff, but getting quantum dot is not somethingso very trivia it needs lot of I would say practical iteration to reach to the pointof obtaining uniform quantum dots.From here we move onto nano composites, so nano composites are multiphase material whereat least one of the constituent phase has 1 dimension less than 100 nanometres, so forexample if the composite of A and B then one of them either the A or B suppose I say Ait should have that nano dimension with it that is 100 nano meter, the promise of nanocomposite lies in their multifunctionality.So you could have the functionality of this and you could have the functionality of B,so both could exhibit different kind of functions and the possibility of realising unique combinationof properties and achievable with traditional Pristine material.So essentially what you are doing say for example of a composite of say the B, A, C,D and if you could really manage to get the phase conditions right, then what you arecatering is a very exotic material with properties of this properties of this properties of thisproperties of this properties of this as well as their interactive properties which emergingout because of their interaction.So these are some of the material which have to profound application if I had to say inagriculture.This is what we are looking forward to in terms of having a compact fertilizer capsulelike you know you have for example nitrogen phosphorus, potash and you know say boron,Silicon you know likewise.So nano composite the whole area of nano composite and confining nano composite into some formof say nano cages for say slow release of active ingredient or confining them in someform of nano belts.Say for example decorating a nano belt with different kind of material as we are mentioningsay A, B, C, D, E and with the amount of surface area what is available for it to react rectangularcross section as I mention.These could have profound impact in terms of using them as material for futuristic agriculture,both from insecticidal, pesticidal and all other wide area of application.So this is basically what we talked about is the structure way of classifying nanomaterialbased on their shape and based on their geometries.And there are many more small nano diamonds and all these kind of things then you havebeads and all.For those nomenclature but at the end of the day what you have to realise that differentkind of nanoparticles or nanomaterials depending on the chemical moeity which is present there,their self assemble in a unique way and we are just in the process of understanding someof these, so today what I have been covering out here in terms of the different shapesmay be 10 years down the line or even 5 years down the line.There will be many more such shapes coming through and maybe a different kind of classificationwhich will emerge through.