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
1. Introduction:
1.1 What are "dispersions" (colloidal systems)?[4]
Let us begin with differentiating them from "solutions": these are homogeneous mixtures of one (or more) chemical species molecularly dispersed in a solvent. That means, that every single molecule (in polymers: every monomer unit) is completely surrounded by the solvent (it is solvated). In contrast to this, in colloidal systems the process of mixing of the pure chemical species (mostly a solid) in a solvent did not lead to a subdivision of the bulk to the molecular level, but to such a fine degree, that very fine particles are (more or less) evenly distributed (dispersed) in the solvent below the micron range, and we are not able to tell by visual inspection, whether we are dealing with solutions or dispersions.
In contrast to solutions, dispersions are heterogeneous on a microscopic scale. We are dealing with (at least) 2-phase-systems, containing a dispersed phase (normally discontinuous) and the dispersion medium (the solvent, continuous). We will consider here only dispersions of solid particles in a liquid medium (more precisely called "sols"), and will not treat aerosols and emulsions in detail.
The colloidal scientists have agreed to call all systems "colloidal" where the dispersed phase is between 1 and 1000 Nanometer (nm). It is self-understood, that these limits cannot be sharp. Below 1 nm, we will find a range where colloidal properties begin to change into those of solutions, because the size of the solvent molecules and the dispersed particles/molecules are becoming more and more similar. Above 1 we will have the transition into the class of suspensions.
