Dr. Bernhard Wessling
Zipperling Kessler / Ormecon Chemie
D-22904 Ahrensburg

Conductive Polymer / Solvent Systems: Solutions or Dispersions?

A Contribution to a Fundamental Approach in this Debate

Abstract:

The title question is being fundamentally discussed by the author. It is the goal of this paper to provide enough data and considerations for deciding, if solutions of conductive polymers ICP (organic metals, OM) can exist, or if such systems, which are called "solutions" may in fact be dispersions. The answer to the question should provide a basis for better understanding of conductive polymer/solvent systems and hence for prediction of results of new experiments.

Basic thermodynamic aspects of solutions and dispersions in general are presented, and applied to either analogous systems (polymers, salts, metals) or specific conductive polymer systems, mainly polyaniline. In the theoretical part, many quantitative or semi-quantitative arguments are developed concerning solubility parameter, surface tension, free energy of dissolution, solution enthalpy, lattice energy, wetting, surface energy reduction and others.

In the experimental part, numerous publications by the author and by other groups reporting about various different experimental studies are summarized and interpreted.

It is shown, that all ICP / OM - solvent systems, which look like solutions, are in fact dispersions. Metallic conductivity and insolubility go together.

Table of Contents

• The goal of this paper

1. Introduction:
   • 1.1 What are "dispersions" (colloidal systems)?[4]
   • 1.2 Origin of surface properties
   • 1.3 Examples of practically important colloids
2. Thermodynamical considerations
   • 2.1 Solutions
     • 2.1.1 Basic solution thermodynamics
     • 2.1.2 Semi-quantitative approach
     • 2.1.3 Estimation for Polyaniline
   • 2.2 Solution properties of salts and metals
   • 2.3 Lattice energy of polyaniline
   • 2.4 Dispersions
   • 2.5 The role of the solvent as solvating or dispersing medium
3. Surface tension of polyaniline
4. Discussing the "solution hypothesis" again
   • 4.1 What indicates that the systems could be true solutions?
     • 4.1.1 Dynamic light scattering of PAni-CSA
     • 4.1.2 Liquid crystalline "solutions"
   • 4.2 What experiments would we need to prove the existence of solutions?
5. What experimental evidence do we have for the "dispersion hypothesis"?
   • 5.1 Own experimental studies
     • 5.1.1 Particle size (morphological)
     • 5.1.2 Particle size (electronically)
     • 5.1.3 Viscosity and gelation
   • 5. 2. Other experimental results
     • 5.2.1 ICP morphology / particle size / coherence length
     • 5.2.2 Concave viscosity curves
     • 5.2.3 "Solubilization" of PAni in water by interpolymer complexation
     • 5.2.4 Wormlike micelles
     • 5.2.5 Soap-like structures
     • 5.2.6 Aggregation of polyoctyl-thiophene
     • 5.2.7 Viscoelasticity
     • 5.2.8 Gel permeation chromatography: changes upon salt or co-solvent
     • 5.2.9 Magnetic susceptibility of polyaniline in "solution"
6. Conclusions

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