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Novel nanocomposites were prepared by blending linear or cyclic poly(ε-caprolactones) with two types of chemically modified carbon nanotubes (CNTs). The low-polydispersity cyclic PCL samples (C-PCLs) were synthesized by click chemistry with a number-average molecular weight (M n) of 22 kg/mol. Linear analogues (L-PCLs) with the same M n value were also prepared. Two types of CNTs were employed (with 1% w/w content): single wall CNTs functionalized with octadecylamine (SWNT-ODA) and multiwall carbon nanotubes grafted with linear PCL chains (i.e., MWNT-g-PCL prepared by ring-opening polymerization on previously functionalized MWNTs with a composition of 10% MWNT and 90% L-PCL). The nanocomposites were characterized by transmission electron microscopy (TEM), polarized light optical microscopy (PLOM), and differential scanning calorimetry (DSC). A nucleating effect was detected in both PCLs when SWNT-ODAs were employed. However, in the case of MWNT-g-PCL, the nanofiller nucleated L-PCL but caused an unexpected antinucleation effect on C-PCL. Another interesting behavior displayed by this novel C-PCL/MWNT-g-PCL nanocomposite (composed of 90% C-PCL, 9% L-PCL, and 1% MWNTs) was not only a reduction in nucleation density and in T c temperatures during cooling from the melt, as expected for an antinucleating agent, but also a decrease in spherulitic growth rate and in overall isothermal crystallization kinetics as compared to C-PCL. The results were explained by realizing that new topological effects were created upon mixing the grafted L-PCL chains within MWNT-g-PCL with C-PCL molecules. When these linear chains come into contact with cyclic PCL chains, a threading effect is produced that dramatically affects chain dynamics by forming a transient entanglement network. As a consequence, cyclic molecules relax and diffuse more slowly than anticipated, decreasing both nucleation and growth kinetics. Results on linear and cyclic PCL blends are also presented here, and they support our explanation of the unexpected antinucleation effect reported for C-PCL/MWNT-g-PCL nanocomposites.

The structure of the meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS 4 ) J-aggregates could be determined by X-ray and electron diffraction methods. A sheet-like architecture reveals the relationship between structure and chirality, optics and shapes of the J-aggregate of the meso 4-sulfonatophenyl-and phenyl-10 substituted porphyrins. The structure of the J-aggregates of H 4 TPPS 4 belongs to the chiral space group P2 1 and includes four porphyrin molecules in its unit cell. The intermolecular stabilization of the zwitterionic units by hydrogen bonding and electrostatic interactions between the positively charged central NH groups and the periphery anionic sulfonato groups results in a structure of porphyrins sheets along the [

Encapsulation of DNA into hydroxyapatite (HAp) has been investigated using a rational approach that involves computer simulation and experimental techniques. The temporal evolution of the radial distribution functions derived from atomistic molecular dynamics simulations of Ca

Structural analyses have been undertaken with the monoclinic and orthorhombic crystalline structures of polyester 4 6. X-ray diffraction patterns performed at 50°C and electron diffraction patterns from single crystals, solution-grown films, and epitaxial crystallizations have been considered. Skew CH 2-CH2-OC(O) bonds and a P121/n1 space group were postulated for the monoclinic structure (R-form). Molecular packing was optimized from electron diffraction data and a final R factor of 0.19 was obtained. The orthorhombic structure ( -form) is characterized by an extended conformation and a molecular packing similar to polyethylene. Thus, an R factor of 0.11 is calculated for a setting angle of 40°, taking into account the electron diffraction data. A regular folding habit is found in the lamellar surfaces of crystals belonging to the -form, whereas an irregular folding habit is characteristic of the R-form.