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
4.2 What experiments would we need to prove the existence of solutions?
Scientists who prefer the opinion that such systems are real solutions should consider to make several key experiments in order to prove their position. By comparing the results with reasonable predictions - and with the results of experiments directed to proving the "dispersion hypothesis" - would lead us more and more to a clear picture.
The following experiments could be useful:
1. melt point depression, to evaluate how many Mol of solvated monomer units are "dissolved" in relation to the expected number
2. measuring the swelling degree induced by the preferred solvents; such experiments would be in accordance with two aspects: first, people say that the increasing problems in dissolving ICPs and especially polyaniline when using very dry material is due to cross-linking - that is exactly, where swelling degree measurements are always made with; second, for determination of solubility parameter, the soluble polymers are cross-linked on purpose in order to measure the swelling alone (without dissolution) - so a potential cross-linking would have happened automatically as an advantage for such experiments;
prediction: that no swelling can be observed; PAni is not cross-linked, but very hard to disperse.
3. recrystallization:
I would be excited if somebody happens to
recrystallize e.g. polyaniline, because single crystals would be an extremely
helpful object for studying and improving PAni and other ICPs[34]; polymers are generally tending to
increase their crystallinity in solution, latest with careful cooling and
subsequent precipitation; I have made this proposal many times in public
without any positive feedback yet; if we were really dealing with true
solutions, I am convinced that there would be a doctorate fellow somewhere in
the world who is capable to overcome potential experimental problems, and will
recrystallize polyaniline as people did in earlier days with proteins and DNA,
real hard to crystallize - but only if they are true solutions!
I am afraid that the preparation of single crystals has to be made by other techniques as recrystallization from solution will not occur;
4. dielectric absorption[35]: it should be possible to determine the difference in such relaxation experiments comparing a system which is a "solution" according to the assumptions of the experimentalist, with another systems where he agrees that this were a "dispersion"; in the frequency range above 1 MHz characteristic dielectric absorption peaks should be detectable due to dipole relaxations; these could be assigned to motions in the polymer backbone only feasible when dissolved; even a stiff molecule will have some additional degrees of freedom in comparison to the chains in a (colloidal) bulk particle; also rod-like molecules are exhibiting a different dielectric response in solution compared to their behavior in bulk;
prediction: there will be no difference being found in our ICP-solvent systems, whether one calls them "solution" or "dispersion";
5. comparison of the primary particle size in bulk and in "solution" (see section below).
