Hi Praveen,

We've had a discussion before in this website regarding polyaniline and its solubility/dispersibility issue. You may find it interesting, too:

https://www.researchgate.net/post/How_can_I_determine_the_molecular_weight_of_polyaniline?ev=home_person_add_comment_question_target

There are eminent scientists suggesting PANI is NOT soluble in any solvents (even in emeraldine base form). They believe polyaniline is only dispersible in good solvents such as NMP. [Please refer to Dr. Bernhard Wessling's page]

By the way, what is the MW of polyaniline you are using? Do you have any obligation on using specific solvents? For instance, can you use NMP instead? if so, you can make PANI in NMP mixtures up to 5 wt.% by adding a small amount of LiCl. The lower the MW, the better the results,

Dear Ehsan Danesh,

Thank you for your replay. can you explain the role of LiCl in the PANI dissolution. I have noticed that the LiCl can dope PANI. Normally doped PANI is insoluble in any solvent.

To be honest, the role is not clear and it depends on whether you accept the fact that PANI is truly soluble or not!!! If you accept that PANI is SOLUBLE, then according to Angelopoulos et al. :

"... salts such as LiCl which complex the polymer via a “pseudo-doping” process, also disrupt the internal pani hydrogen-bonding and deaggregate the polymer..."

[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8044840]

Dear Praveen

Try DMSO(Di methyl sulphoxide) it is quite good solvent it dissolves well

Ehsan Danesh said: The lower the MW, the better the results,

And there's the rub... If you have very low MW, say 2 repeat units per molecule, you get excellent dispersion, possibly even dissolution. But the conductivity is so low that it is better expressed as RESISTIVITY. So, high MW = higher conductivty = nearly INTRACTABLE. Low MW = lower condcutivity = better dispersibility. You have to find the trade-off that fits your application.

Praveen, is there some particular reason you need to use dimethyl acetamide and DMF?

it is correct that Polyaniline is truely INSOLUBLE. Please check my publication "conductive polymers - solution or dispersion". This is not a question of belief or no-belief, but a question of thermodynamiccs and facts. My publication summarizes all the facts available about "solution or dispersion", and there is no evidence at all that any solution is possible.

Moreover, I am describing which experiments one wozld have to make with which results if one want to prove a solution is possible.

What you see in case somebody tells you "here is a solution" is nothing else than a good dispersopn with nanoparticles down to 5 - 10 nm.

LiCl role in preparing such dispersion is to increase the ionic strength of the medium and thereby improving dispersibility.

it is not quite difficult to dissolve conductive polymers in any solvent, it is impossible, and I think I have shown this in a very detailed and deep paper. Please go to this link in RG:

https://www.researchgate.net/publication/229428580_Conductive_Polymer__Solvent_systems_solutions_or_dispersions(Can_conductive_polymers_form_true_solutions)httpwww.organic-nanometal.dewww2ResearchSynthmetcontent.html

If you disagree, please deliver facts, not assumptions.

Chapter Conductive Polymer / Solvent systems: solutions or dispersio...

If it is impossible to dissolve polyaniline than this position strikes through a lot of publications using measurements of PANI molecular mass and molecular mass distribution in PANI solutions. These values are convincingly bound with different PANI properties. As to me these numerous facts strongly testify to existence of true PANI molecular solutions.

Alexander, partially correct what you wrote: "If it is impossible to dissolve polyaniline than this position strikes through a lot of publications using measurements of PANI molecular mass and molecular mass distribution in PANI solutions." All these molecular mass measurements are simply wrong.

But with your final statement, you are not correct: There are no facts whatsoever testifying the existence of truel PAni molecular solutions. Please read the paper which I cited above, this paper describes in detail (with all experimental evidence and with theoretical supporting by thermodynamics) that (and why) no truel PAni solutions can exist.

The publication even has a chapter describing what one would need to find in experiments if such solutions were to exist. No one has ever since successfully done such experiments.

You can also use this link:

https://www.researchgate.net/publication/229428580_Conductive_Polymer__Solvent_systems_solutions_or_dispersions(Can_conductive_polymers_form_true_solutions)httpwww.organic-nanometal.dewww2ResearchSynthmetcontent.html

Chapter Conductive Polymer / Solvent systems: solutions or dispersio...

I give you one additional convincing fact:

You can make optically active PAni using optically active (chiral) counterions, like D-campher-sulfonic acid (follow publications of the Wallace group from Australia). Then you can remove the counterions by neutralisation.

Already then, the optical activity should be lost because the optically active counterions are gone, right? but it is still optically active, in fact, as before, much stronger than what the counterions exhibit as optical activity. This already leads to the assumption that the PAni chains will have formed a helix, in this case all (or most) of them in one sense (right or left handed helix).

Now you "dissolve" this neutral PAni - you would assume then the molecules would be "dissolved" and the helices loose their turning sense, right?

But that is not what is happening: the optical activity remains unchanged.

Why? because you did not dissolve, but only disperse the fine particles which does not affect the coformation of the chains.

By the way: the helical structure of the chains is also consistent with my structure model for PAni:

https://www.researchgate.net/publication/49593603_New_Insight_into_Organic_Metal_Polyaniline_Morphology_and_Structure?ev=srch_pub

Article New Insight into Organic Metal Polyaniline Morphology and Structure

I would like to add one more aspect: it is not the case that I am coming out with these conclusions only recently now, no, in contrast: I have given numerous presentations on numerous conferences since mid of the 80s, and this topic was subject of a lot of controversial discussion on many ICSMs and other conferences / seminars; I also have critisized all these authors of MW determination papers when using GPC, and I gave all the evidence why it is not applicable.

But nobody listened or cared about it.

Bernhard, do you also do not believe to the osmometric measurements of PANI molecular mass?

http://www.sciencedirect.com/science/article/pii/S0379677907000197

I think These data are really the approval of PANI truly solution

Alexander,

it is not a question of belief whether or not PAni can truely be dissolved and form a true solution. As long as the facts which I have collected (and published) showing PAni can not form true solutions (but nice dispersions to the eye "looking" like solution), I conclude that PAni is truely insoluble.

Also my thermodynamic considerations have to be proven wrong.

Alternatively, one could do the experiments which I have proposed for proving true solutions and show that true solutions exist.

Also colloidal dispersions show osmotic pressure which can be measured.

The only applicable method to determine molecular weight of PAni is MALDI-ToF, and you will be surprised how low the MW is!

I read the chapter and in my opinion the thermodinamic could be right but different factors are not taken into account, first of all it is supposed that PANI is a solid with a crystalline structure. From XRD analyses of many synthetised PANI it is possible to conclude that to obtain a crystallization from PANI is not the rule but the exception. If only these thermodinamic consideration were used it should be concluded that any polymer is insoluble, in solution polimers are present not as a single rigid rod but many times as a compact coil, I immagine that a high MW single chain present itself as a sferical nanoparticle that could arrive to 5nm diameter and more. Polymers can be soluble and with melting point higher than degradation temperature, the more significative example are cellulose and starch both with high number of hydrogen bonding, both crystalline and both soluble using the right solvent and the right procedure. Another example is PEEK that because of high stability melt at 350 °C without decomposing and still is completely soluble in H2SO4 even if he has high MW.

Sergio, thanks for your comments, please allow me to answer:

First, I did not study the question whether or not PAni is soluble by thermodynamics only - I made it experimentally. In all the solvents which I have used and which had been capable of preparing something which visually looks like a solution, we found particles (Laser Doppler Method). And, very important: when lowering the concentration, the particle size DECREASED while in polymer *solutions* the particle size increases (the coils can expland more).

When increasing concentration, at a very low concentration you get a gel. When taking this gel and freeze-dry it, we find the same particles as before (only now aligned in "pearl-chains").

Second, the nature of the crystallinity for Polyaniline is different from what is usually described in literature. Please look into this article:

https://www.researchgate.net/publication/49593603_New_Insight_into_Organic_Metal_Polyaniline_Morphology_and_Structure?ev=srch_pub

Third, single chains of Polyaniline with its counterions would be charge-wise "unbalanced" from one side. Please sit down and draw a polyaniline chain, then put the counterions somewhere - how do you compensate the positive charge on the chain from the "left" side if you put the counterion on the "right" side, and how would that negative charge be buffered from its "right" side?

Fourth, now exerimentally again: when using optically active counterions to prepare PAni, you get a strongly optically active PAni (by the way, MUCh stronger optically active than the counterion is). Now you remove the optically active counterion and get the (blue) neutral PAni, Emeraldine base. Now you prepare a "solution", let's say in NMP or DMF. What would you expect if it were a true solution? ........ Right, the optical activity must go away - but it doesn't! Hence PAni's optical activity was created by inducing only (or preferably) one direction of the helical chain, and the blue EB "solution" was not a solution in which the single (neutral!) polymer chains could freely move, but also had been solid particles in dispersion, and the chain arrangement did not change.

This leads you back to the article I mentioned above where you find the structure model for PAni, and why I made the model is I made it:

https://www.researchgate.net/publication/49593603_New_Insight_into_Organic_Metal_Polyaniline_Morphology_and_Structure?ev=srch_pub

If one does not "believe" PAni is insoluble, alternatively, one could do the experiments which I have proposed for proving true solutions and show that true solutions exist.

To your last argument: I am not familiar enough with PEEK, but when looking into the web, PEEK can withstand H2SO4 up to 200°C, then would be attacked:

http://www.netmotion.com/htm_files/wh_properties.htm

The dissolution of PEEK in concentrated sulfuric acids will not be a true physical dissolution, but first a chemical modification (sulfonation), then the sulfonated PEEK dissolves in H2SO4:

http://ajse.kfupm.edu.sa/articles/282b_05p.pdf

Can you recover clean (unsulfonated) PEEK from a conc H2SO4 solution? I would assume No.

I hope I could show - although here in brief, the details can be found in the book chapter

https://www.researchgate.net/publication/253651172_Conductive_Polymers_as_Organic_Nanometals?ev=srch_pub

The thermodynamical considerations are "only" for trying to explain what we had experimentally observed.

Article New Insight into Organic Metal Polyaniline Morphology and Structure

Chapter Conductive Polymers as Organic Nanometals

And what about the product specifications in Sigma Aldrich (http://www.sigmaaldrich.com/catalog/product/aldrich/476706?lang=en®ion=IL) regarding the solubility of emeraldine base polyaniline (Mw 10,000)? They say it is soluble in m-cresol, DMAC, DMF, DMSO, NMP.

Elena, Aldrich is not the "pope of Polyaniline" :-), and they do not make their own research. That company which supplies them with Emeraldine base probably claims what you were citing, not Aldrich themselves. But still my experimental facts and many others from literature show that PAni can only (but very nicely) be dispersed.

In my above longer statement I was describing research results which clearly prove that also Emeraldine base is not truely soluble:

"Fourth, now exerimentally again: when using optically active counterions to prepare PAni, you get a strongly optically active PAni (by the way, MUCh stronger optically active than the counterion is). Now you remove the optically active counterion and get the (blue) neutral PAni, Emeraldine base. Now you prepare a "solution", let's say in NMP or DMF. What would you expect if it were a true solution? ........ Right, the optical activity must go away - but it doesn't! Hence PAni's optical activity was created by inducing only (or preferably) one direction of the helical chain, and the blue EB "solution" was not a solution in which the single (neutral!) polymer chains could freely move, but also had been solid particles in dispersion, and the chain arrangement did not change."

Let's consider, that PANI doesn't dissolve, then does it means that the only way to cover metal nanoparticles with the layer of PANI is the direct synthesis of the polymer on the surface of the metal particles?

no, it means you can deposit PAni on metal particles by immersing those particles in a PAni dispersion. The nature (morphology, properties ...) of such a coating is better controllable and more pure than if using direct synthesis, but principally similar.

(by the way: you say "let's consider ..."; fine, nice - but you can convince yourself by reading my papers and in case you don't "believe" - again, I repeat: this is not a question of belief! it's science! it's about facts which can experimentally be proven / disproven! -, so in case you still con't believe you can do the experiments which I suggested at the end of this paper:

https://www.researchgate.net/publication/229428580_Conductive_Polymer__Solvent_systems_solutions_or_dispersions(Can_conductive_polymers_form_true_solutions)httpwww.organic-nanometal.dewww2ResearchSynthmetcontent.html

and you can also repeat the experiments I did (and described in the above paper) and collect the results yourself.

Chapter Conductive Polymer / Solvent systems: solutions or dispersio...