Charged Gels and Membranes

The series on 'Charged and Reactive Polymers' was set forth in two volumes concern ing the fundamentals and applications of polyelectrolytes. A follow-up on 'Charged Gels and Membranes' would therefore seem appropriate, necessitating, however, some explanation for non-specialists. Theories of the most dilute gels originate in that of concentrated polyelectrolytes: the methods and problems are similar in structural, spectroscopic or thermodynamic properties. The borderline can be situated in dialysis conducted with a 'bag' imper meable to polyelectrolytes but not to small ions, solutes and water. One may recall Donnan's use of such a system to experiment and discover his famous law of unequal distribution of ions of different charge inside and out. Remark ably so, it is the difference in scale which characterizes the difference between poly electrolyte solutions and gels and membranes: the colloidal solution of macro molecules is heterogeneous only on the microscopic level, whereas the gel-solution system is a macroscopically heterogeneous one. A gel is formed when weak or strong cohesive forces counterbalance the dispersing ones (usually by crosslinking) without inhibiting the penetration of solvent and of small solutes into the polymeric network. The solvophile macromolecules cannot invade the total volume of liquid. As a result of phase-segregation excess solution and gel coexist and interact. The macroscopic swelling depends on gel cross-linking as well as on ionic concentration and type and ion-selectivities are observed.

Klappentext

The series on 'Charged and Reactive Polymers' was set forth in two volumes concern­ ing the fundamentals and applications of polyelectrolytes. A follow-up on 'Charged Gels and Membranes' would therefore seem appropriate, necessitating, however, some explanation for non-specialists. Theories of the most dilute gels originate in that of concentrated polyelectrolytes: the methods and problems are similar in structural, spectroscopic or thermodynamic properties. The borderline can be situated in dialysis conducted with a 'bag' imper­ meable to polyelectrolytes but not to small ions, solutes and water. One may recall Donnan's use of such a system to experiment and discover his famous law of unequal distribution of ions of different charge inside and out. Remark­ ably so, it is the difference in scale which characterizes the difference between poly­ electrolyte solutions and gels and membranes: the colloidal solution of macro­ molecules is heterogeneous only on the microscopic level, whereas the gel-solution system is a macroscopically heterogeneous one. A gel is formed when weak or strong cohesive forces counterbalance the dispersing ones (usually by crosslinking) without inhibiting the penetration of solvent and of small solutes into the polymeric network. The solvophile macromolecules cannot invade the total volume of liquid. As a result of phase-segregation excess solution and gel coexist and interact. The macroscopic swelling depends on gel cross-linking as well as on ionic concentration and type and ion-selectivities are observed.

Inhalt
I. Opening Lectures.- The Early Developments of the Electrochemistry of Polymer Membranes.- The Development of the Modern Membrane Concepts and the Relations to Biological Phenomena.- II. Equilibria.- The Nature of the Selective Binding of Ions by Polyelectrolyte Gels: Volume and Entropy Change Criteria.- Swelling of Polyelectrolyte Gels and Thermodynamic Parameters of Solvation.- III. Irreversible Thermodynamics.- Some Uses for Membrane Transport Coefficients.- Interaction in Ion Exchangers. Ionic Interactions in a Polyelectrolyte Gel System with Counter-Ions of Different Valence Types and Varying Dielectric Constants.- Interpretation of Membrane Phenomena, using Irreversible Thermodynamics. Comparison of Observed Transport Properties with Those Predicted from a Salt Model Calculation.- Measurement of Fluxes and Forces at the Surface of Cation Exchange Membranes under Conditions of Controlled Polarization. I: Methodology.- Measurement of Fluxes and Forces at the Surface of Cation-Exchange Membranes under Conditions of Controlled Polarization. II: Application of Measurement Use of Phenomenological Coefficients.- Transconformation Surface Reaction and Hydrodynamic Stability.- IV. Ultra- and Hyper-Filtration Membranes.- Fixed-Charge Ultrafiltration Membranes.- Osmosis and Ion Transport in Charged Porous Membranes: A Macroscopic, Mechanistic Model.- Membrane Potentials of Asymmetric Cellulose Acetate Membranes.- Polarization at Membrane-Solution Interfaces in Reverse Osmosis (Hyperfiltration).