HiPco single-walled carbon nanotubes (SWNTs) have been sidewall-functionalized with phthalocyanine addends following two different approaches: a straightforward Prato reaction with N-octylglycine and a formyl-containing phthalocyanine, and a stepwise approach that involves a former Prato cycloaddition to the double bonds of SWNTs using p-formyl benzoic acid followed by esterification of the derivatized nanotubes with an appropriate phthalocyanine molecule. The two materials obtained by these routes comprise different carbon/Pc-addenda ratios, as evidenced by Raman, TGA, and photophysical studies. The occurrence of electron transfer from photoexcited phthalocyanines to the nanotube framework in these ZnPc-SWNT ensembles is observed in transient absorption experiments, which confirm the absorption of the one-electron oxidized ZnPc cation and the concomitant bleaching of the van Hove singularities typical from SWNTs. Charge-separation (i.e., 2.0 x 1010 s(-1)) and charge-recombination (i.e., 1.5 x 106 s(-1)) dynamics reveal a notable stabilization of the radical ion pair product in dimethylformamide.

The relationship between microstructure and mechanical properties has been investigated in Argiope trifasciata dragline silk fibers (major ampullate silk, MAS) by X-ray diffraction, Raman spectroscopy and tensile testing. We have analyzed three fractions of the material, i.e. amorphous, highly oriented nanocrystals and weakly oriented material, for different values of the macroscopic alignment parameter a, calculated as the relative difference between the length of the fiber and its length when supercontracted. Two distinct regimes have been identified: for low values of the alignment parameter a, microstructural changes are dominated by the reorientation of the nanocrystals; however, at high values (a > 0.5) of the alignment parameter, an increase in the fraction of the crystalline phase is revealed. The two regimes are also reflected in the mechanical behaviour, which can be explained by microstructural changes. This finding of the two distinct regimes in the microstructural evolution, which separates the reorientation and the increase in the crystalline phase, will be valuable to develop and validate molecular models of natural and artificial silk fibers, as well as to deepen our present knowledge of the origin of the outstanding properties of MAS fibers. In addition, we have analyzed the characteristics of the crystal lattice, and discussed the relationship between the percentage of short sidechain residues and the unit cell dimensions in different silks.

The mechanical behavior and microstructure of bioinspired fibers spun from solutions of recombinant spidroin-like proteins were extensively characterized, and compared with those of natural spider silk fibers. It is confirmed that high performance bioinspired fibers indistinguishable from natural spider silk up to large strains can be produced through genetic engineering and conventional spinning technologies. It is also found that fibers spun from spidroin-like proteins that contain different motifs of sequence exhibit variations in their microstructure in terms of crystallinity and chain alignment, but these differences are not reflected in distinct tensile properties. This similarity in terms of their mechanical behavior indicates that bioinspired fibers are largely independent of their exact sequence of recombinant proteins and, in particular, of their proline content. Finally, it is shown that the largest differences between natural and bioinspired fibers are found at very large deformations, marking the ultimate challenge in the synthesis of silk-like fibers.

High-performance regenerated silkworm Bombyx mori silk fibers with new properties that mimic those of spider silk can be produced through a wet spinning process modified with an immersion postspinning drawing (IPSD) step. IPSD fibers show the ability to recover from irreversible deformation, and their tensile behavior can be tailored repeatedly, features solely exhibited until now by natural spider silk. It is further shown that the new properties emerge from a microstructure that is closer to that of spider than to natural silkworm silk. This work demonstrates that processing plays a role at least comparable to that of the amino acid sequence in the final properties of the material. The spinning process does not only modify the mechanical parameters of the fiber but also can even prompt the emergence of new properties, opening a wide range of new applications for regenerated silk fibers. It also represents a significant change of the paradigm in the field of biomimetics, given that it relaxes the condition of copying the natural protein sequences as close as possible to recover the outstanding properties of the natural materials.

The mechanical behavior and microstructure of minor ampullate gland silk (miS) of two orb-web spinning species, Argiope trifasciata and Nephila inaurata, were extensively characterized, enabling detailed comparison with other silks. The similarities and differences exhibited by miS when compared with the intensively studied major ampullate gland silk (MAS) and silkworm (Bombyx mori) silk offer a genuine opportunity for testing some of the hypotheses proposed to correlate microstructure and tensile properties in silk. In this work, we show that miSs of different species show similar properties, even when fibers spun by spiders that diverged over 100 million years are compared. The tensile properties of miS are comparable to those of MAS when tested in air, significantly in terms of work to fracture, but differ considerably when tested in water. In particular, miS does not show a supercontraction effect and an associated ground state. In this regard, the behavior of miS in water is similar to that of B. mori silk, and it is shown that the initial elastic modulus of both fibers can be explained using a common model. Intriguingly, the microstructural parameters measured in miS are comparable to those of MAS and considerably different from those found in B. mori. This fact suggests that some critical microstructural information is still missing in our description of silks, and our results suggest that the hydrophilicity of the lateral groups or the large scale organization of the sequences might be routes worth exploring.

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Raman measurements in high quality InN nanocolumns display a coupled LO phonon-plasmon mode together with uncoupled phonons. The coupled mode is attributed to the spontaneous accumulation of electrons on the lateral surfaces of the nanocolumns. For increasing growth temperature, the electron density decreases as the growth rate increases. The present results indicate that electron accumulation layers do not only form on polar surfaces of InN but also occur on nonpolar ones. According to recent calculations, we attribute the electron surface accumulation to the temperature dependent In-rich surface reconstruction on the nanocolumn sidewalls.

The structural damage induced by ion irradiation on dielectric materials and associated device degradation has been, so far, explained on the basis of collisional processes mostly ignoring the electronic excitation. Recent work, focused on lithium niobate, offers conclusive evidence that at high ion energy and moderate mass (A ≥ 15) electronic excitation may induce a giant enhancement over the damage rate due to nuclear collisions. As a consequence the material becomes amorphized at irradiation fluences far below those required for nuclear collisions alone. These results are expected to have a deep impact on many technologies including storage of radioactive waste, radiation‐resistant materials for fusion reactors, lifetime of components and devices in space missions, nano‐patterning in electronics and photonics, and possibly heavy‐ion therapy in medicine. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)