Nafion Totally Explained (original) (raw)

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General
Systematic name See Article
Common names Nafion
Molecular formula C7HF13O5S . C2F4
Molar mass See Article
CAS number [31175-20-9]
Related compounds
Related compounds Aciplex Flemion Dowew Fumasep
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Nafion® is a sulfonated tetrafluorethylene copolymer discovered in the late 1960s by Walther Grot of DuPont de Nemours. It is the first of a class of synthetic polymers with ionic properties which are called ionomers. Nafion's unique ionic properties are a result of incorporating perfluorovinyl ether groups terminated with sulfonate groups onto a tetrafluoroethylene (Teflon) backbone. Nafion has received a considerable amount of attention as a proton conductor for proton exchange membrane (PEM) fuel cells because of its excellent thermal and mechanical stability.
The chemical basis of Nafion's superior conductive properties remain a focus of research. Protons on the SO3H (sulfonic acid) groups "hop" from one acid site to another. Pores allow movement of cations but the membranes don't conduct anions or electrons. Nafion can be manufactured with various cationic conductivities.

Nomenclature and molecular weight

Nafion can be produced as both a powder resin and a copolymer and has therefore acquired several IUPAC names. Nafion-H, for example, includes the following systematic names:

Structure/morphology

The morphology of Nafion membranes is a matter of continuing study to allow for greater control on its properties. Other properties must be related to the Nafion structure such as water management, hydration stability at high temperatures, electro-osmotic drag, as well as the mechanical, thermal, and oxidative stability . The first model for Nafion, called the Cluster-Channel or Cluster-Network Model, consisted of an equal distribution of sulfonate ion clusters (also described as 'inverted micelles'
The difficulty in determining the exact structure of Nafion stems from inconsistent solubility and crystalline structure among its various derivatives. Advanced morphological models have included a core-shell model where the ion-rich core is surrounded by an ion poor shell, a rod model where the sulfonic groups arrange into crystal-like rods, and a sandwich model where the polymer forms two layers whose sulfonic groups attract across an aqueous layer where transport occurs. Nafion is also often cited for theoretical potential (for example, thus far untested) in a number of fields. With consideration of Nafion's wide functionality, only the most significant will be discussed below.

Chlor-alkali production cell membrane

Chlorine and sodium/potassium hydroxide are among the most produced commodity chemicals in the United States. Modern production methods produce Cl2 and NaOH/KOH from the electrolysis of brine using a Nafion membrane between half-cells. Before the use of Nafion, industries used mercury containing sodium amalgam to separate sodium metal from cells or asbestos diaphragms to allow for transfer of sodium ions between half cells; both technologies were developed in the latter half of the 19th century. The disadvantages of these systems is worker safety and environmental concerns associated with mercury and asbestos, although economical factors also played a part. Nafion was the direct result of the chlor-alkali industry addressing these concerns; Nafion could tolerate the high temperatures, high electrical currents, and corrosive environment of the electrolytic cells. � :
Acylation
The amount of Nafion-H needed catalyze the acylation of benzene with aroyl chloride is 10-30% less than the Friedel-Crafts catalyst:
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Catalysis of Protection groups
Nafion-H increases reaction rates of protection via dihydropyran or o-trialkylsilation of alcohols, phenol, and carboxylic acids.
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Isomerization
Nafion can catalyze a 1,2-hydride shift.
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Recently scientists have been able to immobilize enzymes within the Nafion by enlarging pores with lipophilic salts. Nafion is able to maintain a structure and pH to provide a stable environment for the enzymes. Application has included catalytic oxidation of adenine dinucleotides.

Sensors

Nafion has found use in the production of sensors, which application in ion-selective, metallicized, optical, and biosensors. What makes Nafion especially interesting is its demonstration in biocompatibility. Nafion has been shown to be stable in cell cultures as well as the human body, and there's considerable research towards the production of higher sensitivity glucose sensors.
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