Macromolecules uncharged

The overall objective of this chapter is to review the fundamental issues involved in the transport of macromolecules in hydrophilic media made of synthetic or naturally occurring uncharged polymers with nanometer-scale pore structure when an electric field is applied. The physical and chemical properties and structural features of hydrophilic polymeric materials will be considered first. Although the emphasis will be on classical polymeric gels, discussion of polymeric solutions and nonclassical gels made of, for example, un-cross-linked macromolecular units such as linear polymers and micelles will also be considered in light of recent interest in these materials for a number of applications... 

Electric interactions are screened by electrolytes. Hence, by adding electrolytes, the adsorption behavior is made to resemble that of uncharged macromolecules (see Fig. 4.17). 

The occurrence of the l.c. state of low molar mass substances is, as described, always related to a defined chemical constitution. The idea is obvious to tie up the mesogenic molecules to a macromolecule by a suitable chemical reaction. Assuming the mesogenic structure of the single molecules is uncharged by polymerization and can be found in the monomer unit of the polymer, it can be expected that the macro-molecules also exhibit the l.c. state. 

In summary, the effect of porosity on electrical conductivity and ion diffusivity in agarose gels is studied. Both electrical conductivity and ion diffusivity increase with porosity. The model obtained from the electrical conductivity data, i.e., Equation (7), can predict the diffusivity of macromolecules in 2% agarose gel for solutes with hydrodynamic radius less than the pore size of the gel. This study suggests that electrical conductivity method used in this study can be applied to investigating diffusion behavior of macromolecules in uncharged porous media. 

For our purposes, adsorption from solution is of more direct relevance than gas adsorption. Most, if not all, topics in the five volumes of FICS Involve one or more elements of it. In the present chapter, the basic elements will be introduced, restricting ourselves to low molecular weight, uncharged adsorbates and solid surfaces. Adsorption of charged species leads to the formation of electrical double layers, which will be treated in chapter 3. Adsorption at fluld/fluid Interfaces follows in Volume III. Adsorption of macromolecules will be Introduced in chapter 5. Between monomers, short oligomers, longer oligomers and polymers there is no sharp transition in the present chapter we shall go as far as non-ionic surfactants, but omit most of the association and micelle formation features, which will be addressed in a later Volume. There will be some emphasis on aqueous systems. 

The value of p is a characteristic of a given macromolecule, and has been shown to depend on its molecular weight and molecular shape (through the frictional coefficient/), and on its net charge q. This simple equation correctly predicts that mobility increases with q, decreases with increasing/, and is equal to zero for uncharged particles. 

Scheutjens-Fleer (SF) Theory. A conceptual model for the effects of NOM on colloidal stability can be developed by using existing theoretical and experimental investigations of polymer and polyelectrolyte adsorption on solid surfaces and of the effects of macromolecules on colloidal stability. The modeling approach begins with the work of Scheutjens and Fleer for uncharged macromolecules, termed here the SF theory (3-5). This approach has been extended to the adsorption of linear flexible strong polyelectrolytes by van der Schee and Lyldema (6), adapted to weak polyelectrolytes (7-9), and applied to particle-particle interactions (8, 10). 

Figure 2. Schematic lattice representation of a macromolecular adsorbed layer showing adsorbed and nonadsorbed uncharged macromolecules. (Reproduced with permission from reference 11. Copyright 1985.)...

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