Fluorinated surfactants, problems

To keep the precipitating polymers in the dispersed state throughout the polymerization, requires steric stabilizers. This problem is classically tackled via copolymerization with fluoroalkylmethacrylates or the addition of fluorinated surfactants, both being only weak steric stabilizers. DeSimone el al. also applied a fluorinated block copolymer,9 proving the superb stabilization efficiency of such systems via a rather small particle size. One goal of the present chapter is therefore an investigation of our fluorinated block copolymers as steric stabilizers in low-cohesion-energy solvents. 

In the switch from CFC to the more polar HFA propellants, one of the major problems has been inadequate solubility of the surfactants (used to stabilize the micronized drag particles) in the HFA. Solubility can be adjusted within the CFC propellant, e.g. CFC 12 is a far better solvent than CFC 11. However, for HFAs, blends do not exist and so solvency can only be addressed by using a cosolvent such as ethanol. It must be remembered that changing the solvency of the propellant will almost certainly affect the all-important vapor pressure and thus the MM AD, the particle velocity and the deposition site. Alternative stabilizers have been investigated and include PVP, fluorinated surfactants and Poloxamers. In addition to solubility effects, difficulties associated with the use of HFAs also include incompatibility with elastomer components in the metering valves. 

Beside modification of the PT catalyst by incorporation of C02-philic groups, other approaches to the problem of the poor solubility of polar compounds in SCCO2 were envisaged. Fluorinated surfactants (perfluoro-polyether ammonium carboxylates) were used as stabilizers of H2O/SCCO2 microemulsions.The nucleo-... 

The use of CFCs circumvents these problems however, CFCs have fallen under exceedingly strict regulation because of environmental concerns and, as a result, are no longer economically viable options as large-scale reaction media. Additionally, many of the fluorinated surfactants typically employed in aqueous... 

Will the fluorinated surfactant cause problems for the product or system ... 

Fluorinated surfactants reduce the surface tension and improve wetting properties of aqueous and oil-based inks [172]. The enhanced wetting is essential for printing on difficult-to-wet surfaces, such as plastics and metals. Fluorinated surfactants also aid pigment dispersion and control problems such as pigment flooding and flotation. 

Because fluorinated surfactants are not biodegradable, their removal from wastewater is an important practical problem. The results obtained by Schrdder [20a] indicate that ionic fluorinated surfactants are strongly adsorbed on sludges and sediments and their concentrations in wastewater are probably low. 

The search for stable perfluorochemical emulsions for biomedical applications has included microemulsions formed by fluorinated surfactants (see Section 4.8). Microemulsions form spontaneously, are thermodynamically stable, and have a small particle size. However, microemulsions have shared with coarser emulsions the toxicity problems associated with fluorinated surfactants. The early microemulsions made with fluorinated surfactants were toxic and viscous. 

Micelle formation of our block copolymers in fluorinated solvents indicates that these polymers might act as stabilizers or surfactants in a number of stabilization problems with high technological impact, e.g., the surface between standard polymers and media with very low cohesion energy such as short-chain hydrocarbons (isopentane, butane, propane), fluorinated solvents (hexafluoroben-zene, perfluoro(methylcyclohexane), perfluorohexane) and supercritical C02. As... 

PFCA salts (e.g., the sodium and ammonium salts) are an industrially important class of anionic PFCA surfactants. Electrochemical fluorination has been employed to manufacture APFO, an emulsifier used in the production of fluoropolymers and other PFCAs. Hydrolysis of the acid fluorides obtained by electrochemical fluorination results either in the free carboxylic acids or the respective salts. A major problem associated with the hydrolysis of PFCA fluorides is the presence of HF from the electrochemical fluorination and the hydrolysis of the PFCA fluorides with water." The technical process of isolating fluoride-free PFCA derivatives has, therefore, been optimized to reduce the fluoride content of the final product to trace amounts. An example of such a process is shown in Figure 18.6. °... 

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