Dielectric relaxation mechanisms in polyoxymethylene/polyurethane/layered silicates hybrid nanocomposites (original) (raw)
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Polymer …, 2011
Ternary hybrid composites composed of polyoxymethylene (POM), polyurethane (PU) and boehmite alumina nanoparticles were produced by melt blending with and without latex pre-compounding. PU latex pre-compounding was employed for the fine dispersion of both the PU and alumina particles within the POM matrix. In this study the electrical properties of the POM/PU/boehmite alumina nanocomposites were examined by means of broadband dielectric spectroscopy over a wide temperature (−100 to 150 • C) and frequency (10 −1 to 10 6 Hz) range. Data were analysed by means of the electric modulus formalism. The recorded relaxations include contributions from both polymers and the inorganic reinforcing phase. In the ternary hybrid systems five distinct relaxation processes were detected. Relaxations were assigned and interpreted by considering the morphology of the corresponding composite. In particular, they were attributed to the γ -mode of POM and/or of PU, the α-mode of PU, the α-mode of POM and to the interfacial polarization process. Finally, the dynamics of all the recorded processes are examined and discussed.
Probing the dielectric response of polyurethane/alumina nanocomposites
Journal of Polymer Science Part B-polymer Physics, 2010
The dielectric properties of polyurethane (PUR) latexboehmite alumina nanocomposites were investigated by means of broadband dielectric spectroscopy in the temperature range À100 C to 70 C. The concentration of the filler (alumina) was kept constant at 10 phr for all specimens, whereas the mean particle diameter (namely 220, 90, and 25 nm) of the incorporated nanoparticles varied accordingly. For reasons of comparison, pure PUR was also examined. Four distinct relaxation modes were recorded in the spectra of all systems. They were attributed to interfacial polarization, glass transition (a-relaxation), local motions of polar side groups, and chain segments (b-relaxation and c-relaxation). All four relaxation processes exhibit a symmetric distribution of relaxation times, which in the case of interfacial polarization, becomes narrower. The intensity of interfacial polarization increases with the reduction of the mean particle diameter indicating enhanced interfacial area.
Comparison dielectric and thermal properties of polyurethane/organoclay nanocomposites
Thermochimica Acta, 2013
Polyurethane composites were obtained with different organoclay contents. The organoclay Na +montmorillonite was dispersed in the PU matrix by mixing method from solution. Na +-montmorillonite was modified with dodecyl ammonium sulphate and 1-methyl-3-octyl imidazolium tetrafluoroborate. The nanocomposites obtained by using different modifier were compared in terms of dielectric and thermal properties. The dispersion state of the organoclay particles and its effect on the thermogravimetric and dielectric properties of the composites was investigated. The characterization of PU/organooclay composites was carried out by means of scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis and X-ray diffraction. The dielectric properties of the PU/organoclay nanocomposites were studied in detail. The obtained PU/organoclay intercalated nanocomposites exhibited better thermal stability and improved lower dielectric constants than the pure PU.
Broadband Dielectric Relaxation Spectroscopy in Polymer Nanocomposites
Macromolecular Symposia, 2008
Dielectric spectroscopy in the frequency domain and thermally stimulated depolarization currents techniques, covering together a broad frequency range (10 À4 -10 9 Hz), were employed to investigate molecular dynamics in relation to structure and morphology in polymeric nanocomposites. Several systems were investigated, three of them with the same epoxy resin matrix and different inclusions (modified smectite clay, conducting carbon nanoparticles and diamond nanoparticles) and two with silica nanofiller (styrene-butadiene rubber/silica and polyimide/ silica nanocomposites). Special attention was paid to the investigation of segmental dynamics associated with the glass transition of the polymer matrix, in combination also with differential scanning calorimetry measurements. Effects of nanoparticles on local (secondary) relaxations and on the overall dielectric behavior were, however, also investigated. Several interesting results were obtained and discussed for each of the particular systems. Two opposite effects seem to be common to the nanocomposites studied and dominate their behavior: (1) immobilization/reduction of mobility of a fraction of the chains at the interface to the inorganic nanoparticles, due to chemical or physical bonds with the particles, and (2) loosened molecular packing of the chains, due to tethering and geometrical confinement, resulting in an increase of free volume and of molecular mobility.
Polymer Nanocomposite Dielectrics – The Role of the
Dielectrics and …, 2005
The incorporation of silica nanoparticles into polyethylene increased the breakdown strength and voltage endurance significantly compared to the incorporation of micron scale fillers. In addition, dielectric spectroscopy showed a decrease in dielectric permittivity for the nanocomposite over the base polymer, and changes in the space charge distribution and dynamics have been documented. The most significant difference between micron scale and nanoscale fillers is the tremendous increase in interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, the bonding between the silica and polyethylene was characterized using Fourier Transformed Infra-red (FTIR) spectroscopy, Electron Paramagnetic Resonance (EPR), and X-ray Photoelectron Spectroscopy (XPS) The picture which is emerging suggests that the enhanced interfacial zone, in addition to particle-polymer bonding, plays a very important role in determining the dielectric behavior of nanocomposites.
Journal of Non-Crystalline Solids, 2002
Epoxy resin(ER)-smectite clay nanocomposites of exfoliated structure were prepared by dispersing the organically modified smectite clay in the ER and subsequent curing at 75 and 130°C. Molecular mobility in the nanocomposites was investigated in relation to micromorphology by broadband dielectric relaxation spectroscopy. The large-scale heterogeneity, characteristic of the ER matrix, is suppressed in the nanocomposites and replaced by small-scale heterogeneity related to the presence of the silicate layers. The overall molecular mobility is found to decrease, in general, in the nanocomposites as compared to the ER matrix. Ó
Dynamics and dielectric properties of polymer/nanoparticle nanocomposites by dielectric spectroscopy
Dynamics and dielec. properties of nanocomposites based on polymer matrixes and different types of nanoparticles, as studied by several authors, have been reviewed. Studies on nanocomposites based both on thermoplastic (conductive, non conductive and liq. crystals) and thermosetting matrixes are presented, with several types of nanoparticles (ceramic, metallic, metal oxide and others) as fillers. Their effect on dielec. properties and mol. dynamics has been analyzed, underlaying the strong effect of the interfaces on them. Theor. models such as those corresponding to the percolation theory proposed by several authors to quantify those effects are presented and compared, discussing the values and evolution of the fitting parameters.
Dielectric relaxation properties in polypropylene–polyurethane composites
Journal of Applied Polymer Science, 1990
AC dielectric relaxation properties of polypropylene/polyurethane composites have been studied. The segmented polyurethane (PUR) component contained a poly(propylene oxide) soft segment, and a diphenyl methane diisocyanate/butanediol hard segment. The molecular weight of the soft segment, the concentration of the latter in the polyurethane phase, and the PUR content of the blends were changed systematically. It was observed that the polypropylene is phase-separated with respect to both PUR segments and that the dielectric relaxation properties are determined largely by the PUR component. Two transitions attributable to the glass transitions of the soft and hard phases, respectively, were observed. The soft segment transition temperature decreases with increasing molecular weight of the latter. The transition temperatures are somewhat dependent on the PUR content in the blend, indicating some interaction between the phases. Model calculations show that these shifts and some intensity anomalies are not due simply to the existence of a heterogeneous structure. The ohmic interfacial relaxation process does not play an important role in the temperature and frequency range studied.
Dielectric relaxations of Acrylic-Polyurethane hybrid materials
Polymer, 2015
In this work we present a dielectric relaxation study of Acrilyc/Polyurethane polymers synthesized via miniemulsion photo-polymerization. Three different samples, both parts of the synthesized hybrid latex (SOL and GEL fractions) and a full acrylic sample as reference have been considered. Besides dielectric experiments using broadband Dielectric Spectroscopy (BDS) technique, complementary Differential Scanning Calorimetry measurements have been performed. The thermodynamic characterization outcomes evidence very similar characteristics of the glass transition phenomena among the investigated samples without any signature of melting/crystallization. However BDS experiments show three well resolved dielectric relaxation processes above Tg, two of them evidence marked differences among the samples. A detail study allows us to provide a molecular origin for these three dielectric relaxation processes in connection with the sample characteristics. In particular, our results show that the characterization of these hybrid Acrylic/PU by BDS can provide access to some of the structural features that would ultimately influence the adhesives properties.
Macromolecules, 2017
Probing the properties of the interfacial layer between the polymer matrix and nanoparticles in polymer nanocomposites (PNCs) remains a challenging task. Here, we apply three methodsa single Havriliak−Negami (HN) function fit, a two HN functions fit, and the heterogeneous model analysis (HMA)to analyze the dielectric spectra of model poly(vinyl acetate)/SiO 2 nanocomposites for the thickness and the average slowing down in dynamics of the interfacial layer. We find the HMA presents the most accurate analysis on both the thickness and dynamics of the interfacial layer, in comparison to the other two methods that have been actively applied in the field. In addition, the dielectric spectra at low temperatures reveal unexpectedly nonmonotonous changes in the secondary relaxation of the polymer with nanoparticle loadings. These results clearly demonstrate that dielectric spectroscopy is an easy and robust method to study a wide range of dynamic properties of the interfacial layer in PNCs.