This paper has been submitted at Nov 4th, 1996, for publication in a
scientific journal and is now subject to the reviewing process.
You may ask for a hardcopy with the complete manuscript, which contains all figures and all
greek symbols.
Everybody
is invited to comment to this paper. I will consider every argument and
comment back.
This is the 3rd revised version.
Dr. Bernhard Wessling
Zipperling Kessler / Ormecon Chemie
D-22949 Ammersbek
Conductive Polymer / Solvent Systems: Solutions or Dispersions?
2.3. Lattice energy of polyaniline
I will now present a first proposal of an estimation of the lattice energy 
U
of polyaniline hydrochloride. This is helpful for understanding, if a
dissolution of PAni by solvating the ions is feasible.
Using the principles of the Born-Haber cycle we could assume that U can be
estimated with the known vaporization energy of aniline Hv, its protonation
affinity Hp, the vaporization and the dissociation energy of HCl, Hv and
Hdiss[11] and the formation energy Hf of
Polyaniline (by oxidative chemical polymerization[12]).
There is an uncertainty if we should define the lattice energy as the separation of all ions at an infinite distance (as it is defined for conventional salts): this would be equivalent to a complete depolymerisation.
The alternative definition could be to assume the dissociation of the negative counterions (and their separation and removal to an infinite distance) and the separation of the poly-positively charged chain from them, by maintaining the polymeric integrity.
Both alternatives may be looked at, and both are to be taken as abstract pictures, not as realistic models. But if we are talking about true solutions, then either the one or the other picture (and the corresponding lattice energy) will be close to the real situation. In case of a dissolution of the single charged chain together with the counterions (and no separation and solvation of the ions) we are considering a process where the energy has to be described as discussed in section 2.1.3.
Using the first alternative (fig 4, inner cycle) we find
= 47 + 72 + 1380 - 877 + 435
= 1057 kJ/mol
The second alternative (fig. 4, outer cycle) involves an estimation of the formation enthalpy of EB(gas). Based on group value contributions for organic compounds[59] DHp (Anix) is 82.83 kJ/mol. Assuming a comparable proton affinity as for the aniline monomer, the lattice energy of ES (HCl) based on the outer cycle would be even higher, around 1140 kJ/mol.
As the hydration energy of chloride is only 395 kJ/mol in water (!), which is known being a non-solvent for polyaniline, and aniline having a much smaller hydration energy, we can be sure, that polyaniline cannot be soluble in water.
So we can also conclude that the system of PAni-HCl in H2SO4which was claimed by Andreatta, Heeger and Smith [27] being "true solution", is definitely not a solution. H2SO4 cannot overcome the lattice energy of PAni, as even water is not able doing it.
As chloride has a much lower solvation energy in organic solvents of any kind, polyaniline cannot be soluble in organic solvents (cf. section 2.2).
