allowed to proceed for 3 h. The product was moved to a separation funnel and an excess of ethanol was added to remove the surfactants and other reagents.Characterization: FESEM images and EDX data were taken with a JEOL JSM-6700 F microscope with an EDX facility. The TEM images were observed with a JEOL EM-2000 EX II microscope. For the TEM analysis, the samples were deposited on a carbon mesh foil supported on a copper grid. The emission spectrum from the silica nanotubes was obtained with a Shimadzu RF-5301 PC spectrofluorophotometer at room temperature. The excitation wavelength for the emission spectrum was 350 nm, which was the maximum absorption wavelength of silica nanotubes dispersed in ethanol.

Molecular-dynamics (MD) simulations have been performed for two amorphous polymers with extremely different mechanical properties, atactic polystyrene (PS) and bisphenol A polycarbonate (PC), in the isotropic state and under load. The glass transition temperatures, Young moduli, yield stresses and strain-hardening moduli are calculated and compared to the experimental data. Both chemistry-specific and mode-coupling aspects of the segmental mobility in the isotropic case and under the uniaxial deformation have been identified. The mobility of the PS segments in the deformation direction is increased drastically beyond the yield point. A weaker increase is observed for PC.

Conformational properties of neutral and charged dendrimers in dilute solutions of different quality have been investigated by a mean-field analytical approach and by Brownian dynamics (BD) computer simulation for systems up to generation six. Radial monomer distribution and mass distribution functions, radii of gyration, and structure factors have been studied as functions of solvent quality, effective charge of the terminal groups, and Debye screening radius. For high-generation dendrimers BD simulations show that the dendrimers hardly fluctuate. Swelling of both neutral and charged dendrimers is reasonably described by a generalized Flory mean-field theory in which the two-body virial term is replaced by the sum of the excluded-volume and two-body attraction terms. A non-Gaussian term taking into account the finite extensibility of spacers and a Coulomb term in the form of the Debye-Hu ¨ckel approximation have been included as well. The θ-point for a single dendrimer molecule is defined as the characteristic energy of the excluded-volume interactions when the linear expansion factor R is equal to unity. In contrast to linear polymers, the θ-point defined in such way is different from that calculated as the characteristic energy when scaling relation for a good-solvent conditions stops to be valid. Dendritic terminal groups are distributed through the whole volume of the molecule, but the maximum of this distribution is shifted toward the periphery with increase of Debye screening radius and effective charge of a terminal group. It is shown that fractal dimension of a neutral dendrimer depends on both its generation number and spacer length.