Fluorocarbon chain length

The relative response of the electron-capture detector to some haloalkylacyl derivatives is sumi rized in Table 8.17 [451]. In general terms, the monochloroacetyl and chlorodifluoroacetyl derivatives provide a greater response than the trifluoroacetyl derivatives. Increasing the fluorocarbon chain length of the fluorocarbonacyl derivatives increases t ir electron-capture detector response without inconveniently increasing their retention times. The heptafluorobutyryl and pentafluoropropionyl derivatives are considered to be the best compromise between detector sensitivity and volatility for most applications. 

Chen KY, Kuo JF. Surface characterization and platelet adhesion studies of aliphatic polyurethanes grafted by fluorocarbon oligomers effect of fluorocarbon chain length and carboxylic acid group. J Mater Sci Mater Med 2002 13(1) 37—45. 

Vicinal fluorine-fluorine couplings have been measured by Ellis et al for a series of perfluorocarboxylate acids and analysed from the point of view of fluorocarbon chain length. 

The minimum surface tension achievable is also much lower for fluorinated surfactants than for nonfluorinated surfactants. The minima of the surface tensions of surfactants with a hydrocarbon hydrophobe are in the range 25-35 mN/m [51-53], whereas those of fluorinated surfactants are as low as 15-20 nM/m or even lower [54]. The surface tension of aqueous solutions above cmc varies only slightly with surfactant concentration. Surface tension above cmc decreases with increasing fluorocarbon chain length and depends on the counterion (Table 4.1). 

In analogy to surfactants with a hydrocarbon chain, the critical micelle concentrations for fluorinated surfactants in an aqueous solution depend on the fluorocarbon chain length and the counterion (Table 6.9) [58,59,75,77,96,139, 146-154] and decrease with increasing hydrophobe chain length. 

Fluorocarbons with a hydrophilic functional group are very active surfactants [23]. Less than 1% of ionic or nonionic surfactants with perfluoroalkyl groups can reduce the surface tension of water from 72 to 15-20 dyne/cm, compared with 25-35dyne/cm for typical hydrocarbon surfactants [24] Perfluoroether surfactants are about as active as their perfluoroalkyl counterparts of similar chain length [25, 26], but fluorosurfactants with more polar alkyl end groups are considerably less active than their perfluoroalkyl analogues (Table 7)... 

It is also interesting to note that the bipyridine complex 131 with a slightly smaller end-branched fluorocarbon chain forms only SmA and SmC phases. In the SmA phase the layer distance (d = 4.8 nm) is significantly shorter than the length... 

In the coagulation of PTFE latices by cationic hydrocarbon surfactants> however, a dilTerent behavior is observed in that only very small differences are observed in the magnitude of the ccc with variation of chain length (Richardson, 1979). This effect is illustrated by the data in Table V. Again, it appears to demonstrate the lack of affinity of hydrocarbon chains for fluorocarbon surfaces. 

A different thermal behavior is observed for those examples in which the hydrocarbon chain length exceeds the length of the fluorocarbon part. Here, no phase transitions other than that to the isotropic liquid occur at elevated temperatures. Indeed, in case of 6, F(CF2)i2(CH2)ir)H, the thermally induced molecular motion of the long hydrocarbon chain is comparable to that of short chained examples at room temperature, shown by Raman spectra, for... 

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