Fluoropolymer membranes properties

Fluoropolymers can be readily processed into membranes which have found applications in ultrafiltration, microfiltration, wastewater treatment, protein adsorption and separation, proton conduction, stimuli-responsive and controlled deliveries, and biotechnology [6-10]. However, the practical applications of fluoropolymer membranes are limited to some extent by their hydrophobic and inert surface properties. 

Thus, the ability to manipulate and control the surface properties of fluoropolymer membranes is of crucial importance to extend and enhance their functionalities. 

The practical applications of fluoropolymer membranes especially in the areas of purification and separation related to potable water production, wastewater treatment and bioprocessing, have been limited to some extent by their hydrophobic and inert surface properties. Among the different modification techniques, graft copolymerization of hydrophilic monomers, or inimers for further surface reactions, from fiuoropolymers has been useful and effective in improving the physicochemical properties of the parent fluoropolymer with minimum alteration of their desirable bulk properties. Apart from fiilly fluorinated polymers, most of the partially fluorinated polymers can dissolve in polar organic solvents, such as Ai,Ai-dimethylformamide (DMF), A,A-dimethylacetamide (DMAc), NMP, and dimethyl sulfoxide (DMSO), but are insoluble in water, alcohols, and hydrocarbons. 

Surface modification of the polymeric membranes via molecular design is one of the most versatile means to improve the surface properties without affecting bulk properties. Surface modification of fluoropolymer membranes, especially for fully fluorinated polymer membranes, such as PTFE membranes, has been of particular interest, due to their physical and chemical inertness. Surface modification of fluoropolymer membranes can be classified into two categories surface coating and surface grafting. 

Due to their physical and chemical inertness, fluoropolymers are resistant to UV irradiation in the wavelength range of 100-400 nm. It is difficult to directly activate the fluoropolymer membrane surface via UV initiation due to its inert property. A photo-initiator, such as benzophenon, is usually needed to initiate the photo graft polymerization process from the fluoropolymer membrane surfaces [130]. Benzophenon was decomposed into radicals. The free radicals are transferred to the fluoropolymer membrane and hydrogen abstraction leads to the generation of initiating radicals. Benzophenon can be coated onto the membrane surface by dipping the membrane in benzophenon solution in an adsorption process [130,131]. This method could... 

In contrast to past environmental problems associated with fluorocarbon refrigerants, the exceptional properties of fluorine in polymers have great environmental value. Some fluoropolymers are enabling green technologies such as hydrogen fuel cells for automobiles and oxygen-selective membranes for cleaner diesel combustion. 

As was noted above, functional fluoropolymers produced by copolymerization of fluoroolefins with functional PFAVE have several unique properties, with the main disadvantage of these materials being the extremely high cost of functional monomers and the resulting high cost of the functional polymers produced from them. The fact that they are so expensive limits their wider industrial application in other fields such as catalysis and membrane separation, except for chlorine-alkali electrolysis and fuel cells, where the only suitable materials are fully fluorinated polymers because of the extreme conditions associated with those processes. 

Modem membranes usually consist of at least two layers one from sulfonic type copolymer and another from carboxylic type copolymer. The membranes are usually reinforced by fluoropolymer fabric to provide better mechanical properties and long lifetimes. The most important properties are considered in detail in the reviews mentioned above10,11 and in a basic text by Seko et al.6... 

Like many other fluoropolymers, Nafion is quite resistant to chemical attack, but the presence of its strong perfluorosulfonic acid groups imparts many of its desirable properties as a proton exchange membrane. Fine dispersions (sometimes incorrectly called solutions) can be generated with alcohol/water treatments. Such dispersions are often critical for the generation of the catalyst electrode structure and the MEAs. Films prepared by simply drying these dispersions are often called recast Nafion, and it is often not realized that its morphology and physical behavior are much different from those of the extruded, more crystalline form. 

Hyflon AD amorphous fluoropolymer is used in optical devices, pellicles in semiconductor manufacture, as a dielectric and as a separation membrane. Small amounts of TDD have been used as a modifier in ethylene-chlorotrifluoroethylene polymers to increase stress crack resistance. Minute amounts of TDD are used also as a modifier in polytetrafluoroethylene to improve elastic modulus, reduce creep and permeability and increase transparency. It has been suggested that the much higher reactivity of TDD and other fluorinated dioxoles relative to other modifiers gives a more uniform distribution of the modifier in the polymer chain that results in a greater increase in the desired properties at lower concentration of modifier in the polymer. 

Membranes which may be used in the removal of alkali metal ions by electrodialysis are those which are impermeable to anions, but which allow the flow therethrough of cations. Such cation-selective membranes should, of course, possess chemical durability, high resistance to oxidation and low electrical resistance in addition to their ion-exchange properties. Homogeneous-type polymeric membranes are preferred, for example, network polymers such as phenol, phenosulfonic acid, formaldehyde condensation polymers and linear polymers such as sulfonated fluoropolymers and copolymers of styrene, vinyl pyridine and divinylbenzene. Such membranes are well known in the art and their selection for use in the method of the invention is well within the skill of the art. 

Since an IPMC functions as a pathway for hydrated cations, its properties will be expected to affect the performance of an IPMC actuator. The membrane materials used in IPMCs have so far been limited to a few commercially available perfluorinated ionic polymers, such as Nafion, and the thickness of the IPMC has also been restricted to the available thickness of the commercial membrane [67]. However, IPMC actuators employing new ionic membranes have now been reported [68]. The membranes are prepared from fluoropolymers grafted with polystyrene sulfonic acid (PSSA). IPMCs assembled with these membranes have been shown to exhibit at least several times larger displacements than the Nafion-based IPMC with similar thickness. 

This chapter presents the preparation and properties of fluorosilicones and some specialty fluoropolymers. The development of various kinds of novel fluorosilicones for membrane-based applications, as well as their fabrication and modification methods, is also described. 

To enhance membrane mechanical and hydro-thermal stability, Jiang et al. prepared a blend of side-chain sulfonated PFCB block copolymer and a PVDF fluoropolymer [129]. The chemical structure of the side-chain sulfonated PFCB ionomer is shown in Scheme 6.32. They evaluated the membrane s fiandamental properties, such as proton conductivity, gas permeability, water uptake, and... 

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