Jan 13, 2006

My work

Some of you asked me to write about my research. Let me begin with a famous quote from Einstein..
You do not really understand something unless you can explain it to your grandmother.
So, I need to do a lot more of explanation or I better dont write anything at all.

I worked for my Ph.D. on a hot area called 'conducting polymers' (CP). We know that polymers (platics, as we generally know) are bad conductors of electricity; but the CPs belong to 'speciality polymers'. This field is younger than me (the inventors won the Nobel Prize in 2000); one important invention in 1990 was that some of the CPs can be used to generate light when a voltage is applied (just like LEDs). That was one major breakthrough in terms of a huge potential for applications. What are they rivals to? Pretty much anything to do with lighting and colors..

Display technology is one area where they have already been brought in the market. Flat-panelled displays based on liquid crystals (LCDs as we call) can be potentially be replaced by these light-emitting polymers. Advantages? Plenty - light weight, flexibility and processability - to name a few. Imagine how it would be to have a roll of plastics which, when you plug in, will light an entire room.. or laptops with flexible display monitors. Also, unlike LCDs where you have to watch the screen straight (due to 'polarized' light), the displays from polymers would emit light in all directions.. so thats a huge plus too.

One important criterion was to be able to access all the colors required for making a complete display. Visible light has VIBGYOR of colors of which B, G and R are called 'primary colors' bcos you can get all the colors (from black to white) by suitably mixing the three of them. Initial work all over the world in this 'color control' showed that you can access them by using different polymers, each of which has a unique 'band gap', which can be explained as

Color --> A certain energy --> Energy gap --> Chemical structure.

Leaves are green bcos they have certain chemicals with the suitable energy gap (such chemicals are called 'chromophores') whereas carrot is red bcos it has a different chromophore which absorb the sunlight differently. All the things I have said so far form the introduction to my work.My work was to get all these different chromophores in different ratios in the same polymer chains so that it would be possible to fine-tune the color of light emitted. One rule of thumb is that as you increase the length of the chromophore, it tends to absorb/emit light towards the right side of the 'VIBGYOR' spectrum.

So, I prepared a series of polymers with different populations of the 'differently long' chromophores. How different? Statistics helped me in that. My chemistry was such that, according to purely random statistical probability, when I populate my polymer with more and more chromophores, their length also tend to increase. And all the polymers could be made to dissolve in a lot of solvents and cast into films. I used to be proud that time that 'We were the first in the world to prepare soluble conducting polymers with different populations of chromophores'. Those polymes emitted blue, green, yellow, orange and red colors, as we expected.

As a chemist, I improved my own method of making the polymers and studied various properties of all of them. We published it in a reputed journal and a lot of research groups in the world were interested in studying our polymers by different physical techniques. That helped in some collaborations by which my polymers flew from one continent to other and gave some interesting results and publications to me.

PS: I wrote this post in the 'first person' mode bcos you people know only me; but my research supervisor was the brain behind all of my work, so, convert I, my etc. to we, our, etc.


Balaji said...

the subject matter went over my head. but your love for it sure comes thro. Good luck!

Nitin said...

yeah, sounds interesting Raju. Good Luck!

Anu said...

Congrats... n thks u taught me something today, I just wish i a teacher like you ard in my 10th when i was trying my level best to balance equations:)


tt_giant said...

Thats good detailing man. Seems like it has a lot of applicability. But how soon would it touch the market?.

mitr_bayarea said...

Raju: Superbly written-very succinct and it brought out your passion for Chemistry and Polymers.

Kudos for your papers and publications. Your sincerity in acknowledging your research prof. was heart warming.

Best of Luck!!!

Nallavan said...

dat was interesting raju. but i fainted halfway thro ;)
all the best

Paurna said...

will have to go through that again.but by the look of it this stream seems fascinating

ram said...

Good Consolidation of ur work in the way everyone could understand

NaiKutti said...

great work raju in writing it down on lay-man terms and not missing the details... the work sure is fascinating and good luck for making a break through...

i have a quick question:

with different populations (and/or lengths) of chromophores we get different colors... but to get a range of colors how is it done... to get red or violet we can accordingly get the right configuration of the chromophore but to get the entire range or atleast RGB how would that be done because when we talk to using CP it needs to display all colors at will without having the need to interfere by adding/removing additional chormophores right?...

i understand that u r working on this effort as the line mentions: ["My work was to get all these different chromophores in different ratios in the same polymer chains so that it would be possible to fine-tune the color of light emitted. One rule of thumb is that as you increase the length of the chromophore, it tends to absorb/emit light towards the right side of the 'VIBGYOR' spectrum."]... would mixing different lengths of chromophores in diff. ratios lead to that? how isotropic would that mixture be interms of emitting all the colors?

i might have missed the point completely and sorry if that was a stupid question but "curiosity doesn't kill the naikutti" unlike "curiosity kills the cat" :-)

Anurama said...

Wow.. romba azhaga explain panni irukeenga Raju. I never had interest in Chemistry - Organic Chemistry always used to drive me crazy. Anda subject-la interest varamaadiri ezhudi irukeengale.. hats off!

:: The Protector :: said...

i havn't loved chemistry, but seems your work brings some breakthrough... all d very best!

Happy Pongal....


Raju said...

Balaji, sorry.. I tried my best to put it as simple and concise as I could.. thanks for ur wishes..
Nitin, yeah, it is a very interesting area.. thanks to u too..
Anu, thanks, though I have to say that these are old (over 5 year old results) I put through here..

I havent proven myself as a teacher at all.. am still 'studying'.. :-) thanks for ur kind words..
Deepak, yeah, it has. The LED part and the stuff that I am working now.. Remember the link I gave a few months ago about the Nobel website about my area? It has lots of potentials..

Some products (displays for mobile fones, shaving machine and a few minor ones) have already come to market.. companies like Phillips, Kodak, Epson and Du Pont are pushing very hard towards all directions..

Raju said...

Mitr, thank you. Yeah, I just love chemistry and polymers.
Sarathy, LOL.. oops.. thanks... :-)
Paurna, yeah, it is a fascinating subject to work.. One of the hottest areas in polymers, materials science and future technology.
Ram, thanks. Hope you liked it...

Raju said...

Karthik, wow.. I didnt expect this discussion to take place here..

on your first para of question: As you can see from the foto of various polymers, we get red to blue light. (These are 'normal' fotos, which means they show only the reflected light; fotos taken under the UV lamps would show different colors - e.g., the right-most vial would glow blue). Though by the chemical methods we did indeed succeed in getting the polymers, the performances of the LEDs made from the ones on the right were not promising. The reason being, having lower population of chromophores, the rest of the population is 'non-conducting' and thus reduces the efficiency of the devices.

R, G and B are the primary colors and the range of colors you talk about would be possible by 'pixeling' technology. Since these polymers are soluble, one can dissolve them and fill in the ink cartridges of a normal deskjet printer in the appropriately colored ones. Similar to how we get all colors from the 3 colors of a normal inkjet printer, one can get differently colored polymers on any substrate.

About your second para of question, that leads to some very complex photo-physics in these polymers, which is very exciting. What happens when you have a single polymer chain having different chromophores is, there is a directional flow of energy from the shorter chromophores to longer ones. Each chromophore has a unique absorption/emission but the energy transfer leads to light emission largely from 'the longest chromophore available' in a single chain of polymer.

Let me make one point clear: First, I make a polymer in which all the chains have only one kind of absorption/emission to start with (which is in the ultra-violet), but have slight differences in the chemical structure. I chemically convert such a polymer into one which emits some color shown in the foto. I dont mix the chromophores to get the polymer.

About the colors, if you look at the 'spectrum' for each polymer, from right to left, it narrows... i.e., it is broad and has emission from several chromophores for the polymers on the right (green). You can call it 'less isotropic'.. whereas the ones towards the left end show a distinct emission spectrum.. so it is more isotropic.

Let me know if I answered your qns./doubts rightly. I might have missed some, considering that I am awake from 2:30 AM, watching this stupid cricket match. time to catch some sleep now.. It was a good question, BTW.. I am glad you understood the concept of these materials and came up with such questions which formed bulk of discussions in my thesis..

I appreciate ur curiosity.. LOL on ur naikutti vs cat reference.. good one..

Nitin said...

raju, i think India galli dhan against Pakistan. very poor bowling

Raju said...

Anu, thanks.. your comment on organic chemistry goes well with this post of mine.. :-)
Vishnu, thanks for ur wishes. As I mentioned, this was a old piece of work.. No breakthrough in technology yet.. but we are happy to have done our bit..
Nitin, yeah.. it was very poor indeed.. no one bowled with control. So many legside deliveries , feeding to the Pak batsmen.. Unless some miracle happens tomorrow, we can simply forget this test. (Now, I am looking keenly on the weather forecast of Lahore.. With tomorrow and sunday expected to be mostly cloudy and showers predicted on Monday and Tuesday, I would rather be happy to see off this game as a draw. :-(

Vijay Ramamurthi said...

Pretty interesting.....
one clarification..probably a dumb one..
one mixture, assuming it has a fixed band gap?? can emit color only in one wavelength rite? the reason i asked coz, i was just curious if it was possible to dynamically change the bandgap which will cause it produce different colors, by its virtue of it being a polymer???

and one more thing just to clarify my concepts and these are direct band gap structures rite?

i dont know much..i have taken one course on semiconductor device theory which was dealing compound semiconductors, incidentally they are direct band gap semis' which are used for making leds and lasers.

sorry if they are dumb questions..

pongal nalvaazhthukkal..

Jayan said...

Hey gp. First pit-stop !!! Will come back for a detailed reading :)

Raju said...

Vijay, no question is a dumb question.. especially when a person in the technology tries to understand something in a totally different subject like chemistry..

One major difference between the solid state semiconductors (that you would have studied) and the conducting polymers is that, unlike in the farmer, where a bandgap is very well defined, in the latter, it is a slightly diffused value. In polymers having more than one type of chromophore, a 'true bandgap' doesnt in principle exist. It would depend on the relative population and the difference in the energies of the chromophores.

And, 'color' is pure only when you have an extremely narrow optical wave, which usually is the case only in lasers. Let me give you an example: A polymer having two chromophores emitting blue and red together would look, say, purple to the human eye but a spectrometer would pick the difference. So, if you have any mixture, you have to worry about the colors and the interactions between the chromophores (energy transfer as I mentioned earlier).

i was just curious if it was possible to dynamically change the bandgap which will cause it produce different colors, by its virtue of it being a polymer??? very interesting question.. Even a single polymer having a defined distribution of chromophores can be made to emit light differently by varying certain parameters such as the solvent used for processing, tempreature, and applied voltage. I wouldnt say it is possible to 'dynamically change the bandgap' but by applying certain things, one can.

I am glad you guys asked me such questions. In fact, some work is still in progress by some of my ex-colleagues in IISc, Bangalore in addressing the issues you have raised.

Pongal Nalvaazhthukkal to you too!!
Jayan, OK.. I will look for more comments/questions when you come back.. :-)

Me too said...

Einstein quote-tellam pottuteenga! Purinjudhunnu solradha, puriyalennu solradha??!!

BTW, when you say "polymers (platics, as we generally know)", is it different from the plastics we generally use? I am so confused with the advantages and disadvantages of plastics. The dependancy on plastics by humans have grown so much that its non-biodegradable nature simply scares me.

NaiKutti said...

raju, thanks for taking time to explain... i thought the chromophores are mixed physically (and not chemically) thats why some questions might have been off-topic... as a follow-up (after reading ur answers to vijay's questions), lemme see if i got this right: u wrote "Even a single polymer having a defined distribution of chromophores can be made to emit light differently by varying certain parameters such as the solvent used for processing, tempreature, and applied voltage. I wouldnt say it is possible to 'dynamically change the bandgap' but by applying certain things, one can." -- so when we want to use in LCD or something similar (i.e., devices where we would require diff colors) would this be done mainly by temperature or voltage? how much variation in temp. would be required to span the RBG range or the VIBGYOR range... again, curious

and cricket match -- very disappointing, u better sleep well today w/o watching the match :-)

div said...

interesting post..

Raju said...

Aparna, edhuvendralum unmai sollalam.. But, I can guess the answer.. Sorry, enakku kidaicha time-la ivlodhaan explain panna mudinjudhu..

Polymers is more of a scientific term whereas plastics is a daily usage one. Poly means many; many-mer is many molecules attached together.. so the polymers are also called macro-molecules. 'Plastics' got its name by virtue of the property, i.e. being plastic (which is oppostite to 'elastic').

The conducting polymers, as I said, are 'speciality polymers', which means they are not prepared in the large scales that commodity polymers (like polythene or polystyrene) are made. To give u an idea, my entire PhD could be completed with less than half a gram (in total) of all the polymers that I made. Since they are expensive to make and also their use limited as a thin film, the conducting polymers for devices would be prepared in a few kilograms. thats all.. Of course, these are also non-biodegradable.

To make a 20 inch LCD screen, I guess about half a gram of polymer would be sufficient.. the screen would thus be very light, which is a driving force for the research in this area.

Raju said...

Karthik, the pleasure is mine..

This qn. of yours is also very good, lemme tell you. Only subtle changes in color are possible by varying the parameters such as temperature, choice of solvent and voltage. e.g., a polymer that 'normally' emits in yellow can be 'pushed' to emit in the yellow-orange or orange. It is a very hot topic of research, which, being undertaken by my erstwhile group at IISc, Bangalore, has not been published in full detail yet.

Full range is impossible to reach from one single polymer.

About the cricket match, the disruptions have become very disappointing.. I wonder what would have happened if we had got another 50 more overs in the match.. Sehwag was unbelievable..

I havent subscribed to live telecase of the match, since it is quite expensive this time (everyone wants to cash on the cricket fever..). So, I only follow the cricinfo scores at times in the night.. thats all..
Divya, thanks..

NaiKutti said...

thanks again for explaining... so if full range is not possible from a single polymer how can these be used for LCDs?... man, i understand am bugging u more :-)... feel free NOT to answer

Raju said...

Karthik, LCDs have liquid crystals.. in the flat-panel displays (which have gone synonymous with LCDs), one can print high-resolution dots, with all three kinds of polymers extremely close to each other and each individually 'addressed' (i mean, connected). When red required, (e.g., some girl's pottu), then only the pixels having the red polymer would get connection and they glow. When pink is required (e.g., a ribbon), then suitable pixels (more of red and less of blue over a large area) would get connection and pink is resulted. It is like color-mixing in printers, as I mentioned earlier.

There is a subtle difference though.. printers use three primary colors, but which are 'substractive' colors, since they have to show color on a white paper. So, if you open a color laser/deskjet printer, you would see pink, yellow and magenta cartridges. By mixing them in different proportions, one can get any color.

Similarly, in displays, pixellation technology helps in getting any color. The key is resolution, to avoid blurring and color mismatch. More the dots, better.

Hope I could explain you the funda of a polymer-based display. Any doubt, plz. dont hesitate to shoot.. :-)

Lalitha ravichandran said...

exciting work.. Polymer work needs lots of hard work, do well

Best wishes

Raju said...

Lalitha, Thank you so much.. Nice to know of people understanding and appreciating the work.. :)

Anonymous said...

There was a lecture by Prof.Alan Heeger in my University. It sounded interesting and now it feels good to hear someone so interested in this field. Just a quick question: How developed are the theoretical/mathematical models in this field?

Raju said...

Anon, Oh.. that is nice.. Alan Heeger's lectures are quite popular.. Glad u have interest in this area.

Theoretical/mathematical models are, I guess, quite well developed. The leader in this subject is Prof. Jean-Luc Bredas of Georgia Tech.. He has written a few review articles on the theoretical stuff.. Prof. Ramasesha from IISc, Bangalore is the pioneer in India.. Do Scifinder searches on them and you will get tons of literature. Good luck!!

Ramya harish said...

Wow... feel so good to listen to chemistry.. I understood ur post..later brainstorming parts.. am just tending to understand.. i was trying to visualise u with a black board n chalk.. i cannot do without a pen n paper.. when it comes to understanding sumthing.. i need figures,..diagrams..:(

Raju said...

Ramya, good to know that someone understood this post..

Blackboard n chalk? LOL.. I dont like that, since chalk gives off too much dust... It has been 9 months since I full course with only blackboard n chalk.. Nowadays, I use mostly powerpoint slides, with occasional help from blackboard for deriving some equations.

Figures and diagrams? I have plenty of those, all in my thesis. Of course, I cant put them in blog, rite? May be when blogging becomes more techno, I will put up a presentation that I gave in IISc 8 years ago..

Ramya harish said...

yeah.. why dont u put up some diagrams/ equations.. or send me some ppt's(rohirums@gmail.com)..

Anonymous said...