No abstract

We report a simple method to synthesize binary polymer brushes from two incompatible polymers of different polarity. The synthetic route is based on a subsequent step-by-step grafting of carboxyl-terminated polystyrene and poly(2-vinylpyridine) to the surface of a Si wafer functionalized with 3-glycidoxypropyltrimethoxysilane. The end-functional polymers were spin-coated on the substrate, and grafting was carried out at a temperature higher than the glass transition temperature of the polymers. The composition of the binary brushes can be regulated based on grafting kinetics of the first polymer by the change of time or/and temperature of grafting. This method reveals a smooth and homogeneous polymer film on the macroscopic scale, while at the nanoscopic scale the system undergoes phase segregation effecting switching/ adaptive properties of the film. Upon exposure to different solvents, the film morphology reversibly switches from "ripple" to "dimple" structures as well as the surface energetic state switches from hydrophobic to hydrophilic. The same switching of hydrophilic/hydrophobic properties was obtained for the different ratios between two grafted polymers in the binary brush.

Considering the important production of carbon nanotubes (CNTs), it is likely that some of them will contaminate the environment during each step of their life cycle. Nevertheless, there is little known about their potential ecotoxicity. Consequently, the impact of CNTs on the environment must be taken into consideration. This work evaluates the potential impact of well characterized double-walled carbon nanotubes (DWNTs) in the amphibian larvae Xenopus laevis under normalized laboratory conditions according to the International Standard micronucleus assay ISO 21427-1:2006 for 12 days of half-static exposure to 0.1-1-10 and 50 mg L(-1) of DWNTs in water. Two different endpoints were carried out: (i) toxicity (mortality and growth of larvae) and (ii) genotoxicity (induction of micronucleated erythrocytes). Moreover, intestine of larvae were analyzed using Raman spectroscopy. The DWNTs synthetized by catalytic chemical vapor deposition (CCVD) were used as produce (experiment I) and the addition of Gum Arabic (GA) was investigated to improve the stability of the aqueous suspensions (experiment II). The results show growth inhibition in larvae exposed to 10 and 50 mg L(-1) of DWNTs with or without GA. No genotoxicity was evidenced in erythrocytes of larvae exposed to DWNTs, except to 1 mg L(-1) of DWNTs with GA suggesting its potential effect in association with DWNTs at the first nonacutely toxic concentration. The Raman analysis confirmed the presence of DWNTs into the lumen of intestine but not in intestinal tissues and cells, nor in the circulating blood of exposed larvae.

The formation of amorphous carbon or graphite from C 60 under neutron irradiation is a logical expectation. Therefore we have recorded the FT-Raman spectra of both the amorphous carbon and graphite as well (Fig. 4). The two sharper graphite D and G bands are observed at 1291 and 1588 cm À1 , respectively. Similar bands were observed for amorphous carbon at 1300 and 1592 cm À1 . The very strong band at 1300 cm À1 indicates the strong disordered structure in amorphous carbon. It is clearly seen that there are no traces of these Raman features in the spectra of irradiated C 60 in Fig. 3. Probably the extent of surface decomposition is very weak, not detectable by conventional FT-Raman spectroscopy but strong enough to destroy to efficiency of Raman scattering.FT-Raman spectroscopic studies of irradiated C 60 crystals indicated a quite early decomposition of the samples already at the lowest neutron dose applied, close to 10 15 n cm [2]. Our earlier positron lifetime spectroscopic and DSC studies [3] indicated that C 60 resists up to a neutron dose of approx 10 16 n cm À2 . This difference can be explained by the fact that Raman spectroscopy is very sensitive to the slight surface decomposition which did not affect the general properties of the bulk material. It was not possible to detect the formation of amorphous carbon or graphite by FT-Raman spectroscopy but weak features of polymerised C 60 were detected. It can be concluded that FT-Raman spectroscopy is a very sensitive tool for the detection of the minor surface decomposition of polycrystalline C 60 .