Dielectric relaxation phenomena and dynamics in polyoxymethylene/polyurethane/alumina hybrid nanocomposites (original) (raw)
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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.
European Polymer Journal, 2017
Polyoxymethylene/Polyurethane/Layered Silicates (POM/PU/LS) ternary hybrid nanocomposites were prepared by two methods: (a) direct melt compounding (DM) and (b) melt compounding using a latex-mediated masterbatch (MB) technique. The morphology of the produced specimens and the quality of the dispersion of LS (synthetic sodium fluorohectorite) were examined via Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Broadband dielectric spectroscopy (BDS) was employed in order to study the dielectric response of the two systems in a wide frequency and temperature range. Rich dielectric spectra are recorded, since dielectric relaxation mechanisms originate from POM matrix, PU latex as well as from interfacial phenomena between LS and the polymer matrix. Six different mechanisms were observed in the spectra of the examined
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.
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.
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.
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.
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.
Relaxation properties of some segmented polyurethane-CaCO3 composites. A Dielectric study
Journal of Polymer Science Part B: Polymer Physics, 1987
Dielectric relaxation in three segmented polyurethane-CaC03 composites was investigated between-7OOC and + 15OOC in the 300 Hz to 100 kHz frequency range. Two of the polymers contained a polyacetal-polyether soft segment, whereas the soft component of the third polymer was polypropylene oxide. The hard segments consisted of 4,4'-diphenyl methane diisocyanate in two cases and toluene-2,4-diisocyanate in the third case. In parallel studies two calorimetric relaxations, designated a and a', were observed for each sample and were determined to be glass transitions of the soft and hard segments, respectively. In general, the transition temperatures decrease with increasing filler content. High frequency, low temperature permittivities increase while low frequency, high temperature AC conductivities generally decrease with increasing filler content. The shift in the transition temperatures can be explained using the adsorption theory of filler-polymer interactions and the densities of the samples. The interfacial polarization mechanism becomes important only above the a' transition temperature and below 1 kHz. EXPERIMENTAL Three different classes of segmented polyurethanes with 0, 25, 40, and 60 vol% filler contents were synthesized and studied. The hard segment of the polymers designated A and B (Figure 1) contained 4,4'-diphenyl methane diisocyanate (MDI; Mobay Chemicals). The chain
Dielectric Spectroscopy of Polystyrene/Poly(ethylene oxide) Composites
Macromolecules, 1996
Dielectric spectra of composites of poly(ethylene oxide), PEO, in polystyrene, PS, have been obtained, as a function of frequency and temperature. The dispersion of a high-dielectric constant, lowglass transition temperature, semicrystalline polymer (PEO) in an amorphous, lower dielectric constant, high-Tg continuum (PS) has enabled the dielectric observation of four molecular relaxation processes in PEO. They are the R relaxation associated with the crystalline melt of PEO; two WLF type relaxations, and ′, which we speculate to be respectively associated with the onset of segmental motion and freevolume expansion of unrestricted amorphous PEO chains and with amorphous PEO chain segments tethered in crystallites; and a sub-Tg, γ relaxation associated with localized motions in the crystalline chain segments. The relaxations associated with the R and ′ processes have not been previously observed dielectrically. In pure, neat PEO, the R and ′ relaxations are obscured by dc losses. The dispersion of PEO as micron-sized and submicron phases in PS enables its full relaxation spectrum to be observed.
Development of polyurethane–titania nanocomposites as dielectric and piezoelectric material
RSC Advances, 2013
Flexible polyurethane (PU)-titania nanocomposites of different compositions are prepared by a meltmixing technique. Two different sequences of mixing method are adapted to prepare two different sets of composites. All these composites show composition-dependent dielectric properties, and composites with tunable dielectric properties can be obtained through judicial adjustment of composition. The morphology of these composites has been investigated by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and scanning probe microscopy (SPM). Dielectric properties at low frequency regions are found to depend on morphology. These composites show excellent piezoelectric behaviour, where the dielectric constant and conductivity of these flexible composites change appreciably with changes in applied stress. The dielectric breakdown strength of these composite is also measured. To understand the thermal stability of these composites, thermogravimetric analysis has been applied and it was found that a composite containing 12.49 vol% titania shows higher thermal stability, beyond which, stability decreases due to the photocatalytic effect of titania.