So, let us start the fortieth lecture today which is on silk bi-material and electricity. So, in the previous lecture I shared the story of Jacobus Ishii and his exploration of understanding the thermo photovoltaic properties of a hornet silk cocoon membrane and this which is also called the silk cap. So, today we will be talking about the other cocoon membranes which is the more traditional ones the bombax mori and the tassar cocoon likewise and we will see whether the observations which were made by Jacobus Ishii during 1970s, 80s and 90s with his seminal work. Do they really hold true for more commonly known silk or is it just a very unique property of the hornet nest. So, as I told you in the previous lecture that in one of the studies it was observed that the regular silk cocoon has a thermo regulatory property that gives a positive hunch that possibly if it has a thermo regulatory property it may have certain currents across its membrane. So, this lecture will be to explore that and further whether these kind of hairy currents or you know very small current could these current be utilized in the era when we are kind of you know facing lot of energy crisis as we are looking for different kind of materials to generate power could these kind of naturally existing material could be utilized you know power some low power electronic devices or not. So, this study will take us from Ishii's original study on hornet nest to the next level of study where we will be dealing with the silk cocoon membranes of bombics and anthria myelita. So, these this is a repetition of the picture what I showed you people. So, if you look at these two cocoon. So, on your left hand side with the A is a bombics cocoon. Bombics is the most commonly used cocoon for the garments across the world. India being the largest producer followed by India and this cocoon is very smooth cocoon and very smooth this silk is very smooth and it does not have a lot of minerals it has very very little mineral constant contents and that is why it is so smooth and so fine. Where is the second one on the B what you see anthria myelita or the tassar cocoon this is also called a wild cocoon because it grows in the wild or sometimes semi domesticated kind of you know. So, this cocoon has lot of mineral contents and that is a challenge in order for the reeling of the fiber because of the lot of mineral contents this cocoon has is kind of a coarse it has a very coarse texture as compared to the texture of the bombics mori cocoon. So, this lecture will be talking about the electrical properties of these two types of cocoons. So, let us look at the ultra structure of these cocoons. So, this is the paper I will be referring to. So, I will be adding this paper in your additional material reading material please go through this paper. So, all the studies what is being shown is will be from this paper. So, that sums up there are three papers what I expect you from the previous lecture those two papers from Jacob Ishe and this paper from scientific reports please go through them. Now, let us move on to the ultra structure. So, if you look at the ultra structure of the silk cocoon membrane on what you see in A is the ultra structure of anthria myelita or the tassar silk and the B what you see is the ultra structure of the bombics mori cocoon. So, if you look at the structure very carefully you will observe in A and B the basic difference is A has lot of you know as if the granules scattered on those sericin fibrin network whereas, you see a very smooth texture in the case of bombics. Now, the upper two panels are showing the outer surface of the silk cocoon if you see the inner because it has been cut into two halves. So, that what you see here is the outer surface and what you see here is the inner surface both inner and the outer. So, the lower two C and D are the pictures of the inner surface which is fairly smooth in both the cases, but in terms of the fiber thickness the fiber is slightly more thicker in the case of the anthria myelita which is the wild type cocoon which is also called the tassar cocoon. And A and B which is the outer surface of the cocoon what is being shown you see the threads are core in course as well as in the case of anthria and you see there is an inset box which is showing some you know in the left hand top corner if you see it those are showing the crystals what you see those the small you know the granules all over the surface it is showing the crystals of calcium oxalate. They have enormous deposition of calcium oxalate on their outer surface. So, this is the basic ultra structure and the basic ultra structure still follows the same A what I told you that inner cylinder inner core cylinder of fibroin this is the fibroin core and this is the gummy part which is the sericin or the sticky protein. And on top of the anthria myelita what you see you see lot of sticky crystals which are present here. These sticky crystals are of calcium oxalate what you see in the inset picture basic geometry is the same there is no difference in the basic geometry except there is one more change what will you observe in the next slide is this one the amount of elements which are present in it. This was also observed by Jacob Ishe while talking about the silk of the hornet nest. So, if you look at it there is significant proportion of calcium sodium potassium chloride magnesium sulphur and copper. Whereas, in the anthria also you pretty much see the same thing except they have zinc which is in significantly higher amount at least not detectable in bomb ex and their phosphorus which is not detectable in bomb ex and of course, the sulphur and all those things are present and the copper which is not detected in the case of anthria. So, if you look at it. So, there are plethora of and the calcium is higher in one of them which is in the anthria calcium is fairly higher and that calcium possibly is coming from the calcium oxalate crystals. Because, there are there in the anthria there is enormous calcium oxalate crystals and that is why the concentration of calcium is very high in case of anthria myelita. Now, if you look at this. So, it means what we are talking about now I am adding one more component to it. So, they have lot of these x are showing the different kind of elements which are present there and one more thing here I want to add all the studies made by Ishe was when you are keeping the cocoon at a slightly higher relative humidity at around 80 percent relative humidity 80 percent to 90 percent relative humidity you are observing all the different currents which are observed by Ishe. It means the ambient water plays certain critical role in charge transfer. So, now moving on to the next slide in order to understand how the cocoon properties could be studied you have to develop certain very specific standard structures. So, what has been done in this study is you took two different cocoon samples you took a piece of bombics and the measurements are given out here. They have a slightly varying thickness that you cannot help it because it is inherent property and you connect it with two different electrodes. So, here let me add they have a certain amount of voltage across the cocoon across the membrane, but that voltage is not very high as was observed by Ishe. So, in order to enhance that self cocoon has its inherent potential difference PD 1 which is indigenous potential difference and now by putting two different electrodes say an aluminum and copper you are adding one more potential difference to that which is the second one. So, the total potential difference is now slightly higher. So, now what you are using it in order to understand because now we are more keen here to see whether this could be used to develop some kind of device or not. We know that there is a flow of current and all those things, but could this be utilized. So, in the next study what has been done by developing these kind of devices the current and voltage are being measured. Now, let us see how the current and voltages are changing. So, if you look at a dry cocoon now on a follow this is a busy slide go to the panel A. So, you see in the panel A in the case of a dry cocoon there is very very little current you could see that the current is very less. Now, if there is a moist cocoon then the current jumps very significantly follow the only the panel A. Now, if you demineralize the cocoon then also you will see a significant amount of current demineralization means you are getting rid of all these x are getting rid of the x out here. So, it means you are getting rid of several charge carriers out there. Now, the current density increases significantly if you see the picture when you are exposing this to water vapor and if you dope it now you are adding n s c l to that a kind of you know ensuring when the coming in contact with water what it will do it will from n a plus ions and c l minus ions what you will observe is the current density goes up. So, same thing in the case of anthria if you follow the section c you see the same thing it is pretty much follows the same trend dry cocoon it is almost acting as an insulating material there is hardly anything, but the very moment there is exposure to moist condition this behaves as if it is a conductor or something like a semi almost behave like a conductor. So, if you remember I was telling you all the issues were follows the relative humidity is at 80 percent or at only at relative humidity 80 percent you see this kind of charge motion, but then you have to realize most of these hornet nest or silk cocoon remain in a area in a kind of a micro environment where there the humidity is higher maybe in a shade in a corner or you know surrounded camouflage by several trees or something the leaves likewise you know. So, those kind of camouflage regions have a micro environment where the relative humidity is slightly higher because there is a transpiration taking place continuously from the leaves and the surrounding vegetation and that kind of increases the relative humidity in that location. So, now if you see the voltage trend you again see the same thing at a dry the voltage is fairly low, but then as you moisten it the voltage goes up it means one thing is very very clear this kind of situation are wet electricity this is not something. So, still the question remains who are the charge carrier in this kind of situation. So, this is the first clue in this study that this kind of materials only functions when it is exposed to or it is kept in a kind of you know high relative humidity. Now, this is a very interesting study to look at what are the thermo electrical properties of it. So, if you follow this graph if you follow the let us follow because the trend is same let us follow in the case of bombics the red line. If you see it as you are moving the red line is showing you the current as the temperature is increasing at around 45. So, there are two rise you are seeing one you are seeing between 10 and you know 25 and then second you are seeing between 45 and 60. So, around 40 45 or so beyond for slightly at around 50 you see a sharp spike of current and you saw such sharp spike of current in case of issues were at around you know 31 32 degree centigrade here you see it at around 45 50 degree centigrade there is a sharp rise spike of current. So, there are two spikes of current and you see the same trend. So, it means this kind of membranes are thermosensitive membranes first conclusion you could draw and during the thermos this thermosensitivity leads to generation of electrical currents. This is what this slide is telling you and this trend is pretty much the same in the case of bombics as well as anthria. So, what I was trying to explain in the previous lecture in the 39th lecture that these membranes have a thermo thermo regulatory role which is governed by flow of thermal current holds true here if you see that depending on the temperature shifts the thermal current is varying as well as the voltage. So, it has certain thermo voltaic property which leads to thermal current generation. Now, if you see the IV characteristics and once again for those who have joined late like you can see all these figures in the reference paper what I have given you. Now, if you look at the IV characteristics you will see the current voltage pattern shifts or changes with respect to temperature. So, there are two IV thing which has been taken at 30 degree centigrade and 80 degree centigrade and if you see it the current density is changing as the temperature is rising and this exactly will remind you what is she did if you remember I will just go back to the slide of is she is here in the hornet cell it is following the very similar trend what you have seen in hornet the current rises when the temperature rises. So, coming back in the IV studies that is what is the IV study is telling you as the temperature rises the current rises now followed by the next study. So, one of the thing is one of the possible explanation to this current could be this is all we are trying to figure out could be all these different elements which are present there in the presence of water vapor. So, the water vapor is getting in a embedded into these zones I will show you a wonderful model after work. So, these water vapors are they are creating different kind of electrolyte materials there could be sodium there could be calcium there could be magnesium likewise different charges chloride you know there are other anions and cations out there and now since these anions and cations are setting across two electrode of different electronegativity there is a possibility that what we may see a charge flow this could be one explanation, but this explanation fails if we look at this picture why in the case of demineralized condition if you see this picture very carefully on the second panel A see the panel A and the orange line a demineralized cocoon and a moist cocoon you see the same situation why is it so, because when you are demineralizing you are essentially getting rid of all these things getting rid of all of that minus these. So, then where are the ions. So, that is a very intriguing question and that is what we are going to go slowly that what possibly could be the explanation, because again coming back to the slide be careful with those that orange line and the violet line just underneath it you see that orange line which is showing demineralized and getting w v as the water vapor and the moist cocoon and the just a water vapor. So, those three lines are very important the green line the orange line and the violet line these three lines are telling you something and we will be talking about what these three lines are telling you, because in those three line lies some of the very fundamental phenomena which is getting orchestrated in between these this membrane. So, coming back in order to see. So, this is a NMR study which was done to see the presence of the water molecules which are present embedded in the cell fibroin matrix as well as the presence of the sodium ions which are present there and those could be detected using the NMR out here. So, it is kind of to show that there are ionic species which are present there. Now, followed by that we have to went ahead and see whether these kind of things. So, we have observed that there are you see these kind of currents are present there. So, at this stage there are two things what we will be dealing with what we will be dealing with is that whether these currents are sufficient enough what you see in the slide out here sufficient enough to you know drive some crude devices or you know could you develop some bioelectrical device to harvest necessary energy from a cocoon or not this is one thing what we are going to answer. Second thing what we are going to answer what are the charge careers. So, I will be answering this charge career thing in the end, but first while we discussing about what are the different devices you can develop out of it. So, here there is some devices device development we are talking about. So, you take the cocoon you could see in the picture very clearly the inside you see there is an aluminium foil which is acting as electrode and outside you see the wrapping of the copper. So, the aluminium and copper electrode which are attached across the cocoon surface. So, now what you see here now when you have this aluminium copper and you are. So, let us concentrate on panel A B C D. So, you have three cocoons out here which are attached by aluminium and copper and they are attached in a C D circuit and you are exposing this to water vapor you will see it could it could generate sufficient power to power an LED light emitting diet. Whereas, you can do the same thing, but we have just shown it here with four different anthraeamylita cocoon. If you connect them in series exactly the shown the way it is you can really glow an LED out of it. So, you can harvest some harvest energy by exposing a cell cocoon to water vapor and water vapor which is at a temperature around 80 to 90 degree centigrade. So, that is the ambient temperature. So, underneath what you see that there is a beaker coming in the panel A from that beaker basically beaker is getting it is boiling water which is you know the water that the water is boiling and the water vapor is coming out and in the presence of water vapor what you see is that the cocoons is started to glow. So, now the question arises that could we really make a very you know this is a very crude device which is exposed to water vapor and likewise, but could we make a much more finer device, but before we get into this let us look at these two panels E and F what the E and F is telling you. One more thing I need to add you can read the paper the reference paper it is free of cost online and you will come across a series of videos where you will be able to appreciate the whole process how these devices are being used to you know generate electricity. You can actually harvest electricity from these devices and please go through those videos because that you will be able to appreciate the whole process much better as compared to you know seeing and still pictured out here. Now what about this E and F what E and F is telling you E and F is there is no water vapor on anything it is a moist cocoon which is charged for a small period of time using a charger you have these battery charges or something you charge it and then disconnect it then you connect a load on it you see an LED which is glowing. So, now you can switch it on switch it off. So, it means the cocoon membrane what we are talking about these proteins which are the assembly which is making the cocoon membrane is acting like a capacitor or a simple charge storage device. This one you have to really see the video then you will be able to appreciate that you can switch it off switch it off switch it on switch it off and you will be able to you know store sufficient amount of charge in them which could be utilized for plethora of applications. So, this is a functional device from the crude cocoon directly using the cocoon by you know the connect connecting the electrode like this and what you see out here you see these two tubes which are coming through. So, you can observe this by you know exposing it to electro to water vapor both outside as well as inside what does that mean. So, let me just rub the board and tell you exactly how this is being done I will just keep that relative humidity out there. So, if you have these cocoons connected in series and what you do you have a tube coming like this that is what you observe you know one c 1 c 2 c 3 likewise and you are giving water vapor like this. So, there are two ways you can do it either you expose the water vapor like this from outside what you are seeing that images something like this to see the slide. So, in the panel A what you are observing is the water vapor is being exposed outside and you can even expose water vapor inside like this and when you are exposing it to the inside then also you see the same effect, but this effect is more pronounced because your water vapor is concentrated inside. So, it is kind of you know confined at a space. So, you see this effect you know much more elegantly out there that it generates sufficient power. Now, coming to a systematic device development. So, here you see that the four cocoons where you know added by you know connecting with these connectors and likewise, but here what is being done it was systematically you know stacked using two different kind of electrodes. So, this is what you see now where there is a systematic device and a systematic device also if you see the videos you will see you can see the same kind of you know current and voltage. You will see these are the current traces what you see as in the presence of water vapor over a period of you know 200 minutes which is almost 3 hours you see significant amount of current and you see the and you see the subsequent voltage in the bombics as well as in anthrium. So, what I essentially wanted to put across is that this membrane behaves in a very very interesting way very similar to what has been documented by Jacobus Ishe and that also gives a lot of confidence to tell that what he observed some you know 40 30 or now almost or 30 years back is pretty much the same what we are observing today with much more you know. So, it means the silk proteins cross the genera probably behave like this they have I mean now we can say with certain degree of confidence that at least 3 of the silky species are showing the same behavior. So, these are the current and voltage of the traces of the devices now we talk about the model what is the proposed model currently accepted model. So, you see here there is a temperature gradient shown at the top from 10 to 60 degree centigrade and likewise and above. Now cocoon membrane has been shown as the outer membrane and the inner membrane you see this. So, you see in the center the outer membrane and if you see the outer membrane has been shown as broken lines it is shown in broken lines because the water absorption from the outside is higher and the inner part is very insulated to water it is almost like a waterproofing membrane. So, if you really could this is the cocoon membrane for example, this is the membrane cross section was observing. So, there will lot of bigger pores here through the water will enter and you know, but this pores density changes like this by the time inside is very very this is almost like a waterproofing membrane this outside. So, this is the kind of gradient you see these are showing the water molecules. So, in other word this membrane is an asymmetric membrane and because of its asymmetry connect an electrode like this you see a very interesting potential drop across it and in this asymmetric membrane there are embedded metal ions which are present there anions and cations sorry which are present there and in the presence of water these ions gets activated. So, if you see in this picture in the slide you will see there is there is this ions and the water molecules in blue and then you have the ions which are all scattered across it and when it is getting sufficient water those ionic species based on the electro negative it is started to flow across the membrane, but what is interesting to know now I will take you back to this slide what we what I was telling you that what is the explanation to this situation when you are demineralizing the cocoon is still you are seeing same current I told you that please concentrate on the green orange and the violet line why they are same they are pretty much same this is something a very mysterious situation. So, it means there is something else probably. So, even if you remove this remove these red ones still you see sufficient amount of current how you explain this situation this situation could be explained in a totally different perspective that is something called proton hopping what essentially happens is even if you get rid of all these different ions this particular temperature zone there is huge amount of at around 80 degree centigrade is a huge amount of movement of the water molecules which are taking place on this surface at a temperature of 80 to 100 degree centigrade enormous movement of water molecules and these water molecules are moving and this is already hydrated there is a lot of proton species which are formed protonic species which are formed there those protonic species possibly could using the word possibly could explain this unusual pattern that even if you have a demineralized cocoon with you or a membrane with you there is no mineral still you see a high density of current present there. So, it means this whole weight electricity what we were discussing is governed by two component one of them is ion which is the charge carrier and ions and once again let us go back to the slide and ions and cations and the second one is protonic possibly these are the two things which are you know governing the flow of current across this membrane this is the most possible explanation, but that takes us it means whether the other kind of membrane could do the similar things and as a matter of fact if you go through the paper what I have recommended you people you will see some of the porous membranes like you know paper if they are sufficiently doped with ionic species they could also conduct current this was a backup or kind of you know supporting information what you will see in the paper. So, coming back to the slide if you look at the slide so if you see a dry paper is acting as a insulator a moist paper also does not show a lot of current, but in the case of water vapor you see a rise in current and if you dope it with NaCl you see even a higher current across it. So, these studies and this model and if you go through this slide where I was talking to you about the green line orange line and the violet line of current tells you that this is a very interesting zone where both ions and possibly the protonic species are responsible for the flow of current across these kind of biological membranes. So, partly where we started in the previous lecture while talking about cliches studies what are the charge carriers we partly answer this question in this lecture possibly the charge carriers are either ions or the protons protonics protonic species is shall could we call it a biological semiconductor well I would not be able to answer that question it is a material when it is dry these kind of biomaterials when they are dry they are insulator, but in the presence of water and varying temperature they are behavior drastically changes and they almost become a conductor and they generate sufficient. So, and if you manipulate the physical parameters these of they generate sufficient amount of current which could power a low power electronic devices and the proposed model is shown here and these are some of the results and this is the proposed model out here and you could do the similar things with porous materials. So, I will close in here and I will request you people please go through these papers they are very interesting papers from Jacob Ishe now and there are lot of room for you know development and understanding for even a better understanding that how different kind of biomaterials could be utilized could be an answer for our quest for clean and green energy. Thank you.


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