Thermodynamic considerations show, that the the melt enthalpy as well as the lattice energy of conductive polymers (organic metals), like polyaniline, cannot be invested by organic solvents, nor by water, which will prevent any possibility of making true solutions of conductive polymers.
The lack of direct experimental evidence for effectively solvated single chains is in accordance with these considerations.
There are many publications in the literature claiming the existence of “true solutions” of conductive polymers (organic metals) in various solvents, including relatively unpolar ones. The key papers have been discussed in detail in [48] with the result, that all phenomena described in these papers can be better understood within the colloidal picture rather than by assuming “true solutions”. This becomes most clear when looking at ESR spectra (Heeger et al [1]). They not only found virtually no difference in the ESR of their PAni in bulk vs. in “solution”, but also no temperature dependence, especially not in solution! This showed - in contrast to their own interpretation - that the nature, size and structure of the metallic unit has not changed when transforming the PAni from the solid state to the state in the solvent. If isolated fully solvated chains would be present in solution, not only a strong temperature dependence, but also a strongly differing ESR behavior would have to be observed. But as the particle size does not change when going from the solid to the dispersed state, the ESR spectra do not change as well.
More evidence for the colloidal character of conductive polymer / solvent systems has been added by interpreting some more publications [48].
Thermodynamical aspects are conclusive according to which the surface tension of conductive polymers (“Organic Metals”) is very high due to very strong intramolecular forces, so that their primary and secondary particles will have solvents (water or others) adsorbed on their surface for reduction of surface energy.
Dispersed systems of ICPs/OM in solvents can be made as soon as the solvent is capable of reducing the previous surface energy. For this purpose, many different techniques might be used, as can be found in the literature.
Metallic conductivity and insolubility of organic metals (conductive polymers, which are polymeric salts) go together and are linked together, because they are based on the same intramolecular electronic interactions, hence very strong intramolecular forces.
The “dispersion concept” does not only have important fundamental, but also practical implications. Whereby the “solution approach” did not yet prove its practical or commercial usability and feasibility, the “dispersion concept” has successfully started to become applied in technical scale since 1993. It should be of interest to the scientist, too, to realize, that by this approach it is possible to cover a virtually unlimited variety of specifications,
- conductivity from 100 S/cm down to 10-9 S/cm
- transparency up to 95%
- processing in thermoplastic polymer systems or in paints/coatings
- processing as pure material (from binder-free dispersions),
- dispersion in many different organic solvents (like DMSO, Xylene, isopropanole) and water,
all of this by using just one single type of raw PAni powder.
Also the non-linear properties and complex (morphological) structures
of the dispersions are not only scientifically extremely interesting and
challenging, but also crucial to understand and control all practical applications,
from antistatic coatings, over corrosion prevention even up to “plastic
lasers”.
