Super-hydrophobicity

Davies J, Maynes D, Webb BW, Woolford B (2006) Laminar flow in a microchannel with super hydrophobic walls exhibiting transverse ribs. Phys Fluids 18 087110... 

Water Solubility and Super-Hydrophobic Properties of CNTs... 

The lotus-like and honeycomb-like aligned CNT films with a combination of micro- and nanostructures were also reported (Sun et al., 2003 Choi et al., 2003). They all displayed super-hydrophobic properties as shown in Fig. 9.14. The well-aligned CNT-polymer films or coatings have potential on applications such as super-hydrophobic surfaces to textiles, coatings, gene delivery, micro-fluid channels, non-wetting liquid transfer, and so forth. 

Some recent examples including uses as super hydrophobic surfaces [142], medical composites of spun fibers, generating scaffolds for cell attachment [138], thermoplastic elastomers [139], as a supramolecular electrolyte in a dye-sensitized solar cell [190], as a method to align polymer chains [191], or as supramolecular polymer composites [192] have been discussed previously. Still there is ample space to be explored and there definitely will be many more patents and applications in this field. 

Gobas et al. [30] in 1989 investigated the bioconcentration potential of polychlorinated biphenyls (PCBs), polybrominated benzenes (PBBzs) and poly-brominated biphenyls (PBBs), and other super-hydrophobic chemicals, such as decachlorobiphenyl and Mirex. These authors also pointed out the importance of bioavailability for bio concentration of super-hydrophobic chemicals. Their study showed that the bioavailable fraction of the super-hydrophobic chemical decachlorobiphenyl can be as low as 3 % and of Mirex can be as low as 2.2 %. For decachlorobiphenyl, a BCF was found that was one to two orders of magnitude lower than the true BCF. 

BCF data reported for very lipophilic and super-hydrophobic chemicals in many cases have been underestimated from experiments with high content of particulate or dissolved organic matter. Bio concentration factors must be related to the bio available chemical concentration in the water, because only the truly dissolved fraction of the chemical is actually bioavailable [5,13,30] (see also Sect. 8.2). 

Furthermore, it was argued by Yen et al. [85],Gobas and Schrap [86],Schwartz [84 c] and Geyer et al. [87,88] that the main reason for the low BCF values of super-hydrophobic chemicals was because they were tested at relatively high concentrations in the water which were some orders of magnitude higher than their water solubility. This indicates that aU these super-hydrophobic chemicals in the... 

In Table 4, the equation to predict the bioaccumulation factor (BAFl) of relatively persistent chemicals in human (fat) is also presented [191, 192]. This equation is only valid for chemicals which are not or only minimal metabolized in human. It is also important to note that for super-hydrophobic chemicals, such as octachlorodibenzo-p-dioxin (OCDD) and Mirex, no steady-state BAF value is reached during the whole life. 

Bioconcentration of Super-Hydrophobic Chemicals and Other Persistent Organic Pollutants (POPs)... 

In the following sections, the physico-chemical properties and the bioconcentration of selected super-hydrophobic persistent organic pollutants (POPs) such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD),octachlorodibenzo-p-dio-xin (OCDD), Mirex, and Toxaphene in fish and other animals will be discussed. 

There is only little information available on bioconcentration using PBDEs in fish and other aquatic organisms. In 1982 the Chemicals Inspection and Testing Institute in Tokyo, Japan, investigated the bio concentration of pentabromobi-phenyl ether in carp [259,293]. The fish were exposed for 8 weeks to commercial pentabromobiphenyl ether at a concentration of 10 and 100 pg 1 The bioconcentration factors (on a wet wt. basis) were more than 10,000. However, it is clear that for such super-hydrophobic chemicals with log values of 6.64 - 6.97 no steady-state is reached after 8 weeks. The second reason that this BCF value was underestimated is that the test chemicals concentration in the water was ca. four to five orders of magnitude higher than the water solubility. The water solubility of pentabromobiphenyl ether (PBDE) is 9 X 10 mg 1 = 0.9 ng 1-1 at20°C [259]. 

TCDD,OCDD,Mirex, penta-, hexa-, hepta-, octa-, nona-, deca-chlorobiphenyl, p,p -DDT, p,p -DDE, p,p -DDD extremely high super-hydrophobic/ or super- lipophilic >6-9 > 1,000,000 >200,000 > 100,000 >50,000 > 10,000... 

To obtain reliable values of k2 or ti/2 it is necessary to measure the elimination of super-hydrophobic compounds from organisms for a long time (some months). 

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