Search

An integrated experimental approach, based on inelastic light-scattering techniques, has been here employed for a multilength scale characterization of networking properties of cyclodextrin nanosponges, a new class of cross-linked polymeric materials built up from natural oligosaccharides cyclodextrins. By using Raman and Brillouin scattering experiments, we performed a detailed inspection of the vibrational dynamics of these polymers over a wide frequency window ranging from gigahertz to terahertz, with the aim of providing physical descriptors correlated to the cross-linking degree and elastic properties of the material. The results seem to suggest that the stiffness of cross-linked polymers can be successfully tuned by acting on the type and the relative amount of the cross-linker during the synthesis of a polymer matrix, predicting and controlling their swelling and entrapment properties. The proposed experimental approach is a useful tool for investigating the structural and physicochemical properties of polymeric network systems.

A detailed experimental and theoretical vibrational analysis of arsenicin A, the first polyarsenical isolated from Nature, is reported. By exploiting the dissimilar and complementary selection rules of infrared (IR) absorption and Raman scattering transitions, and by carrying out density functional theory (DFT) calculations on several candidate structures, we are able to determine the structure of arsenicin A. We demonstrate that vibrational spectroscopy can be a very useful tool in structure elucidation in cases where mass spectrometry (MS) measurements lead to unreliable information, and nuclear magnetic resonance (NMR) investigations are hindered by the presence of silent nuclei, and/or elements of symmetry, in the molecule. Our approach allows to establish a reliable methodology, based on molecular vibrational parameters, for the structural elucidation of any unknown organic compounds of medium-small size on which, nowadays, accurate theoretical calculations can be carried out in reasonable times, without resorting to large-dimension computing resources.

In this work the room temperature electrical conductivity of Si(B) OC glasses made via polymer pyrolysis at 1200°C and 1400°C (maximum temperature) and having different amount of boron was measured. When B content is increased from zero (pure Si OC glass) up to B/Si=0.5 the electrical conductivity increases in 2 orders of magnitude from 4.09±0.64×10−5 up to 2.93±1.91×10−3 with a corresponding decrease in the activation energy from about 1.08 to 0.51 eV. This results shows for the first time that the electrical conductivity of Si-based polymer-derived ceramics can be controlled by the amount of the doping element. The structure of the Si(B) OC glasses has been studied with different techniques including FT- IR, XRD and Raman spectroscopy. The Raman study indicates that B partially substitutes C into the sp2 C planes of the free carbon phase forming trigonal BC3 units. Accordingly, the evolution of the electrical properties with the B content has been correlated with the corresponding structural evolution and a hypothesis is presented to rationalize the role of boron on the electrical conductivity of Si OBC glasses. [ABSTRACT FROM AUTHOR]

The vibrational dynamics of a new class of cross-linked polymers obtained from both native and modified cyclodextrin, referred to as cyclodextrin nanosponges, is here investigated. The main purpose is to spot the structure of these materials at molecular level unlikely to be characterized by diffraction methods due to the low or null degree of crystallinity. The analysis of the spectral features of the vibrational bands observed between 1650 and 1800 cm−1 in both Raman and infrared spectra, and assigned to the carbonyl stretching modes of the polymeric network, is performed by using band deconvolution procedures. At the same time, a detailed inspection of the low-wavenumber vibrational dynamics of these polymers is carried out, focusing on the modifications occurring on the so-called boson peak. The simultaneous analysis of different wavenumber ranges in Raman and infrared spectra of cyclodextrin nanosponges allows us to develop a reliable strategy for exploring both the cross-linking degree and the elastic properties of these innovative materials. The overall results give a complete characterization of the structural and dynamical properties of the system, in turn strictly connected to the entrapment/transport ability of these polymeric matrices. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this letter, we report the formation of bulk samples of silica-based glass containing Si nanocrystals (Si-ncs) by pyrolysis of a preceramic precursor. The starting precursor is a sol– gel-derived polysiloxane containing only Si–H groups which leads, after annealing in a controlled atmosphere in the range 1000–1200 ?C, to the precipitation of Si-ncs. Characterization of the nanostructure was performed by x-ray diffraction and Raman scattering analyses. Room-temperature luminescence experiments show the interesting optical properties of the Si-ncs/SiO[sub;2] material. [ABSTRACT FROM AUTHOR]