No abstract

No abstract

No abstract

The fraction of the polymer located at the nanoparticle–polymer interface in polymer nanocomposites (PNCs) [interfacial rigid amorphous fraction (RAFfiller)] is under extensive investigation as it is generally considered responsible for the modified properties of PNCs as compared to the neat polymers. In semicrystalline PNCs, an additional interfacial polymer exists in the vicinity of crystals, that is, the RAFcrystal, with the properties of the latter (structure and dynamics) being also under investigation. While the presence of nanoparticles and/or crystals themselves can be directly correlated with the modified PNC properties (e.g., mechanical performance), the respective direct effects of the RAFs have been rarely demonstrated. In a recent work, we studied RAF in PNCs based on two different polymers, amorphous stryrene butadiene rubber, wherein RAF = RAFfiller, and semicrystalline low-density polyethylene wherein RAF ≈ RAFcrystal, filled with carbon nanotubes (CNTs), and we revealed quite systematic dependences of thermal diffusivity α on the amount of RAF at each matrix. Strikingly, the α­(RAF) trends were diverse for the two matrices, namely, RAFcrystal, which facilitates heat transport, and RAFfiller, which hinders heat transport. In the present work, we checked the latter α­(RAF) trends in different PNCs based however on the same polylactide matrix at the amorphous and semicrystalline states, filled with small amounts of thermally conductive CNTs and graphene oxide platelets. Results for α­(RAF) here were interestingly found similar with those in the previous study. These findings supply additional evidence for the different structural characteristics exhibited by the two types of RAF, a still open debate in the literature; namely, polymer chains exhibit higher level of ordering in RAFcrystal as compared to RAFfiller. Finally, we propose that RAFfiller can be used as a measure of the phonon’s scattering in PNCs, whereas RAFcrystal in conjunction with bulk crystallites forms additional thermal diffusion paths.

In this work, syndiotactic polypropylene/multiwalled carbon nanotubes (MWCNT) nanocomposites, in various concentrations, were produced using melt mixing. The influence of the addition of MWCNT on the morphology, crystalline form, and the thermal and electrical properties of the polymer matrix was studied. To that aim, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, and dielectric relaxation spectroscopy were employed. Significant alterations of both the crystallization behavior and the thermal properties of the matrix were found on addition of the carbon nanotubes: conversion of the disordered crystalline form I to the ordered one, increase of the crystallization temperature and the degree of crystallinity, and decrease of the glass transition temperature and the heat capacity jump. Finally, the electrical percolation threshold was found between 2.5-3.0 wt.% MWCNT. For comparison purposes, the results of the system studied here are also correlated with the findings from a previous work on the isotactic polypropylene/MWCNT system.

The morphology, microhardness, and electrical properties of composites consisting of conductive polypyrrole (PPy) dispersed into a nonconductive polypropylene matrix (PP) as pure component or in form of a sodium montmorillonite/PPy (MMT/PPy) composite have been studied. For comparison, also PP/MMT composites were studied. All types of composites were processed by compression molding or by melt mixing followed by compression molding into plates, which were used for characterization. Scanning electron microscopy and transmission electron microscopy was used to examine the morphology of the prepared materials. The investigation of electrical and dielectric properties was done by dielectric relaxation spectroscopy in a wide frequency range and was related to the composite composition and processing method. The analysis of the conductivity as a function of temperature indicated that the charge transfer mechanism could be described by the variable range hopping model in three dimensions. The microhardness of PP/MMT/PPy composites with different content of MMT or PPy was determined and the creep rate has been estimated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 407–423, 2009

The results are reported of an experiment designed to measure the force exerted by a current circuit on a part of itself and to compare this to the predictions of the Biot-Savart and Ampere magnetostatic force laws. The design of the experiment was such as to limit the current through the circuits to values below about 1 A, to optimise the removal of the heat generated in the conductors and to minimise the magnetohydrodynamic and other effects in the mercury at the contact points between the two sections of the circuits. Contrary to previously reported results, agreement between experiment and theory is found, within 1 to 2%, which is the limit set by experimental uncertainties.

C/AST/PEG nanocomposites with fumed AST (89 wt % Al 2 O 3 , 10 wt % SiO 2 , 1 wt % TiO 2 ), activated carbon, and poly(ethylene glycol), PEG, were prepared in a wide range of PEG and C/AST (1 : 9) contents. Thermal transitions (mainly in a PEG phase) were investigated by differential scanning calorimetry. The dynamic behavior was investigated by thermally stimulated depolarization current and dielectric relaxation spectroscopy. The PEG crystallinity degree decreases in the nanocomposites, in particular at C PEG 40 wt %. A significant fraction of amorphous polymer is immobilized at a filler surface making no contribution to the glass transition, whereas the rest exhibits a lower glass transition temperature, when compared with bulk polymer, because of loosened molecular packing of the chains. Several relaxations arising from the polymer matrix, the filler, and their combination were identified and analyzed. The segmental a-relaxation of the PEG matrix was found to become faster in the nanocomposites.