Doping with HCl will increase the conductivity of polyaniline. This value is close to 1 siemen. If you remove the dopant completely pani act as insulated and it conductivity value is nearly 10-8 siemen.  Similarly other dopant like PTS, SDS and camphor sulfonic acid show high conductivity.. Mostly 1.0 M HCl was used for the preparation of conducting polyaniline. There is not much influence while increasing HCl concentration.

1M HCl is mostly used. You need to keep just for 12-16 h. 42% doping is normal. Going further is difficult as the doping has to be done against large concentration of dopant present along the polymer chain

thanks all

What exactly do you want to do?\Make a conductive thin film of conductive PANI on glass? Did you do a literature search? I suggest you look at our patent WO2002037536 Solutions of Conducting Polyaniline. Note that we state in the text that these are DISPERSIONS, not true solutions. As you should know, conductive PANI is completely insoluble. We prepared up to 5% by weight of PANI in the mix, and created films with conductivity of about 10 S/cm. Our "carrier" was formic acid, which is readily stripped in a vacuum oven, or with rather low heat in a regular oven (with steps taken to capture the evolved formic acid). Note that because the dopant is included in the mixture, you don't need to go through a doping process after the film is formed. So all of the difficulties involved with getting well-doped films are overcome. Also, we found HCl is NOT the best dopant. Rather, methane sulfonic acid (MSA) is the best that we found. Also, using MSA in place of HCl in the synthesis gives better properties.

I don't remember for certain now, but I think we made highly flexible conductive films by including a flexible polymer in a solvent, and adding this to the mix. We made these conductive films on polyester sheets that produced a nice bend radius without cracking.

You might also want to check EP 1008148 B1 Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom. This teaches how to prepare "solutions" of emeraldaine base at 15-30%. Films can then be subsequently made conductive by immersion in dopant, as you are trying to do.

I think you will also find interesting US 4983322 A Solution processible forms of electrically conductive polyaniline. About the best they get for conductive films is 1 S/cm.

HCl is the worst you can use for doping because it creates side reactions (covalently bound Cl, can not be removed by de-doping action using basic media). Plus, it is not very thermally stable.

The HCl (or any other acid) concentration is not critical,. just apply the acid in excess of PAni - but then wash! and wash! and wash! (using water) the result ideally and optimally should be a dopant (Cl-) / aniline monomer unit relation of 1:2 (elemental analysis: Cl:N should be 1:2, but it would be better to avoid HCl)

Hello Prof. Wessling,

The idea to synthesis pani in HCl medium under ice cold condition to achieve large molecular weight as well as high conductivity. If you synthesis under room temperature the reaction is very slow and there is a possibility to form precipitates of lower molecular weight less conducting polyaniline. I have done enormous amount work on pani. Sometime the dedoped pani can be used to make a processable pani and a soluble one. In some case secondary doping also people have done.  C.C. Han publish a US patent on synthesis of pani with wide ranges of dopant. 

@Kannaiyan, You can see in our patent mentioned above that we did the synthesis at about -10 C. We compared using HCl and methane sulfonic acid (and other acids) in the synthesis and found the MSA resulted in the highest conductivity in the final product. (And also when the emeraldIne base form was was doped with various acids, MSA gave the highest conductivity, possibly due to a "memory effect" when using the same acid for both synthesis and doping.) For highest quality and conductivity, HCl do pant is not recommended.  If you just need some "OK" conductive PANI, then HCl dopant could be OK.

By the way, NMP (I assume that is N-methylpyrrolidone) is not a very good choice of solvent (dispersant) if you want a good film that has reliable adhesion. I can tell you from experience that it is impossible to remove all of the NMP from the film. I suggest butyrolactone. It will disperse the PANI nearly as well as NMP,  but because it has a higher vapor pressure and lower boiling point than NMP, it is much easier to remove. 

Pandian, Regit, as you may see from literature on my RG site, I have published tons of work on PAni. I was finally the first and only one (with my company Ormecon) who really itroduced PAni into the market, in mass production. You can find about the research and introduction history on my web site and here in RG as well.

Some quick statements:

1) HCl is the worst dopant you could choose, I commented several times why. Take pTs, that's the best.

2) MSA allows for apparently highest conductivity only because with MSA doping, PAni absorbs lots of water. If you dry strongly, conductivity drops. With MSA, PAni is ot thermally stable.

3) low temperature is good.

4) please read my various publications (you may take the handbook review chapters first) where I commented about "soluble" and "molecular weight". I am tired commenting - why do you always repeat old stuff which has never been shown to be correct? PAni is not soluble (insoluble in ANY solvent!) so you can not measure the molecular weight by GPC comparing with soluble PS standard!

Anyway you are worrying about HCl. Any dopant we can use but the purpose is different.

again thanks all for their nice attention,

I carefully read your replies and I am going to use them in my project

I am not at all worried about HCl, I only say it is the worst dopant one can use. And please study my publications which show in detail that and why PAni can not be soluble.

Well I will say, HCL is a pretty good choice than conc. H2SO4, a monobasic acid and an organic base, it could be perfect for having good conductivity, maybe you should try with equal concentration(0.1 N) and 100ml to get the good results.

Ms. Tavasoli, first, NMP is not a good choice for the dispersion medium. it has ahigh boiling point and very low vapor pressure, making it extremely difficult to remove. I would be very surprised if your "dry" film does not contain traces of NMP. I suggest That you replace it with butyrolactone. 

Second , if you insist on using HCl as the dopant, concentration is not of much importance . you need to simply add enough HCl to achieve maximum doping; the literature is filled with this information . Both the academic and patent literatures have all the details that you need . 

for the dopants, I can only repeat and say: HCl is the worst you can choose as dopant; it makes side reactions (PAni becomes partially chlorinated) and is unstable; I prefer para-toluene sulfonic acid.

for the dispersion medium, butyrolactone is not a good choice as the lactone group will at least partially be saponified; NMP can relatively easily be removed after film deposition -

- dry the film first by putting the film substrate onto some heater surface,

- then improve drying by using an infrared lamp

- then you can easily wash the film with CHCl2 or else (don't use acetone - kato-aldol cndensation!)