Broadband dielectric spectroscopy is used to inves- tigate molecular dynamics and charge transport in three hyper- branched polyester amides with hydroxyl, phenyl, and stearate terminal groups. At higher temperatures, the dielectric spectra are interpreted in terms of hopping conduction in a spatially randomly varying energy landscape, whereas two secondary dipolar relaxations attributed to librations of the terminal and amide groups dominate the low temperature regime. Despite a shift of more than 3 decades in the dc conductivity upon varia- tion of the end groups, the Barton-Nakajima-Namikawa rela- tion is shown to hold. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1651-1657, 2010

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/polb.21966

Secondary relaxations and electrical conductivity in hyperbranched polyester amides

Structure and molecular dynamics of hyperbranched polymeric systems with urethane and urea linkages

Two methods were employed to prepare hyperbranched polyamine ester (HPAE)/kaolinite (Ka) nanocomposites resulting in different morphologies. In the case of the in situ polymerization, diethanolamine is inserted as monomer between the Ka layers and polymerized with methyl acrylate to prepare HPAE/Ka–DEA nanocomposites. For the ex situ method, Ka is modified with dodecylamine and solution-blended with HPAE. The former method leads to an intercalated morphology where the latter approach results in an exfoliated structure, as proofed by SAXS and TEM. A complementary combination of methods like differential scanning calorimetry (DSC), broadband dielectric relaxation (BDS), and specific heat spectroscopy (SHS) was used to investigate both kinds of nanocomposites in detail. Above Tg, the dielectric spectra are dominated by the conductivity contribution while the segmental dynamics is retrieved by SHS. A comparison of the temperature dependencies reveals a decoupling of segmental dynamics and conductivity, which ...

/pdf/structure-property-relationships-of-hyperbranched-polymer-1nt3no7zly.pdf

Structure–Property Relationships of Hyperbranched Polymer/Kaolinite Nanocomposites

The effect of thermal cycling treatment on mechanical properties and thermal stability of a Zr41Ti14Cu125Ni10Be225 bulk metallic glass is investigated The metallic glassy samples are sealed into quartz tubes under high vacuum condition, and liquid nitrogen together with electric furnace are used to control a periodical temperature variation between 196°C and 150°C The structure and properties of the tested samples for different thermal cycles have been examined by X-ray diffraction analysis, mechanical properties measurement and thermal analysis It has been found that the structure and properties of the samples do not show a significant change even after 200 cycles, which suggests Zr41Ti14Cu125Ni10Be225 alloy as having potential in aerospace environment bulk metallic glass, thermal cycling, mechanical properties, thermal stability

Effect of thermal cycling on the mechanical properties of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 alloy

Understanding the glass transition requires getting the picture of the dynamical processes that intervene in it. Glass-forming liquids show a characteristic decoupling of relaxation processes when they are cooled down towards the glassy state. The faster (βJG) process is still under scrutiny, and its full explanation necessitates information at the microscopic scale. To this aim, nuclear γ-resonance time-domain interferometry (TDI) has been utilized to investigate 5-methyl-2-hexanol, a hydrogen-bonded liquid with a pronounced βJG process as measured by dielectric spectroscopy. TDI probes in fact the center-of-mass, molecular dynamics at scattering-vectors corresponding to both inter- and intra-molecular distances. Our measurements demonstrate that, in the undercooled liquid phase, the βJG relaxation can be visualized as a spatially-restricted rearrangement of molecules within the cage of their closest neighbours accompanied by larger excursions which reach out at least the inter-molecular scale and are related to cage-breaking events. In-cage rattling and cage-breaking processes therefore coexist in the βJG relaxation.

/pdf/a-microscopic-look-at-the-johari-goldstein-relaxation-in-a-h6zp9ygbs8.pdf

A microscopic look at the Johari-Goldstein relaxation in a hydrogen-bonded glass-former

Broadband dielectric spectroscopy is employed to investigate the non-Debye relaxation behavior in a dendrimeric alkyd resin. From temperature-dependent measurements at ambient pressure, we found a very broad distribution of relaxation times. This is attributed to the complex geometrical topology of the molecule. However, compression significantly reduces the non-Debye character of the dielectric response; thus, pressure induces dynamic homogeneity in the dendrimeric alkyd resin.

K. Mańczyk

Papers

Effect of pressure on dynamic heterogeneity in dendrimeric alkyd resin.