198 research outputs found
Particles with selective wetting affect spinodal decomposition microstructures
We have used mesoscale simulations to study the effect of immobile particles
on microstructure formation during spinodal decomposition in ternary mixtures
such as polymer blends. Specifically, we have explored a regime of
interparticle spacings (which are a few times the characteristic spinodal
length scale) in which we might expect interesting new effects arising from
interactions among wetting, spinodal decomposition and coarsening. In this
paper, we report three new effects for systems in which the particle phase has
a strong preference for being wetted by one of the components (say, A). In the
presence of particles, microstructures are not bicontinuous in a symmetric
mixture. An asymmetric mixture, on the other hand, first forms a
non-bicontinuous microstructure which then evolves into a bicontinuous one at
intermediate times. Moreover, while wetting of the particle phase by the
preferred component (A) creates alternating A-rich and B-rich layers around the
particles, curvature-driven coarsening leads to shrinking and disappearance of
the first A-rich layer, leaving a layer of the non-preferred component in
contact with the particle. At late simulation times, domains of the matrix
components coarsen following the Lifshitz-Slyozov-Wagner law, .Comment: Accepted for publication in PCCP on 24th May 201
Exchange bias phenomenology and models of core/shell nanoparticles
Some of the main experimental observations related to the occurrence of
exchange bias in magnetic systems are reviewed, focusing the attention on the
peculiar phenomenology associated to nanoparticles with core/shell structure as
compared to thin film bilayers. The main open questions posed by the
experimental observations are presented and contrasted to existing theories and
models for exchange bias formulated up to date. We also present results of
simulations based on a simple model of a core/shell nanoparticle in which the
values of microscopic parameters such as anisotropy and exchange constants can
be tuned in the core, shell and at the interfacial regions, offering new
insight on the microscopic origin of the experimental phenomenology. A detailed
study of the of the magnetic order of the interfacial spins shows compelling
evidence that most of the experimentally observed effects can be qualitatively
accounted within the context of this model and allows also to quantify the
magnitude of the loop shifts with striking agreement with the macroscopic
observed values.Comment: 17 pages, 10 figures. Review article, submitted to J. Nanosci.
Nanotechnol. (special Issue on Nanomagnetism), invited contribution.
Suggestions and comments are welcome. A copy with higher resolution of Fig. 7
may be obtained at this web site: http://hermes.ffn.ub.es/oscar/Articles.htm
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Does the Processing Method Resulting in Different States of an Interconnected Network of Multiwalled Carbon Nanotubes in Polymeric Blend Nanocomposites Affect EMI Shielding Properties?
Electromagnetic interference (EMI), an unwanted phenomenon, often affects the reliability of precise electronic circuitry. To prevent this, an effective shielding is prerequisite to protect the electronic devices. In this study, an attempt was made to understand how processing of polymeric blend nanocomposites involving multiwalled carbon nanotubes (MWCNTs) affects the evolving interconnected network structure of MWCNTs and eventually their EMI shielding properties. Thereby, the overall blend morphology and especially the connectivity of the polycarbonate (PC) component, in which the MWCNTs tend to migrate, as well as the perfectness of their migration, and the state of nanotube dispersion are considered. For this purpose, blends of varying composition of PC and poly(methyl methacrylate) were chosen as a model system as they show a phase diagram with lower critical solution temperature type of characteristic. Such blends were processed in two different ways: solution mixing (from the homogeneous state) and melt mixing (in the biphasic state). In both the processes, MWCNTs (3 wt %) were mixed into the blends, and the evolved structures (after phase separation induced by annealing in solution-mixed blends) and the quenched structures (as the blends exit the extruder) were systematically studied using transmission electron microscopy (TEM). Both the set of blends were subjected to the same thermal history, however, under different conditions such as under quiescent conditions (in the case of solution mixing) and under shear (in the case of melt mixing). The electrical volume conductivity and the evolved morphologies of these blend nanocomposites were evaluated and correlated with the measured EMI shielding behavior. The results indicated that irrespective of the type of processing, the MWCNTs localized in the PC component; driven by thermodynamic factors and depending on the blend composition, sea-island, cocontinuous, and phase-inverted structures evolved. Interestingly, the better interconnected network structures of MWCNTs observed using TEM in the solution-mixed samples together with larger nanotube lengths resulted in higher EMI shielding properties (-27 dB at 18 GHz) even if slightly higher electrical volume conductivities were observed in melt-mixed samples. Moreover, the shielding was absorption-driven, facilitated by the dense network of MWCNTs in the PC component of the blends, at any given concentration of nanotubes. Taken together, this study highlights the effects of different blend nanocomposite preparation methods (solution and melt) and the developed morphology and nanotube network structure in MWCNT filled blend nanocomposites on the EMI shielding behavior
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Does the Type of Polymer and Carbon Nanotube Structure Control the Electromagnetic Shielding in Melt-Mixed Polymer Nanocomposites?
A suitable polymer matrix and well dispersed conducting fillers forming an electrically conducting network are the prime requisites for modern age electromagnetic shield designing. An effective polymer-based shield material is designed that can attenuate 99.9% of incident electromagnetic (EM) radiation at a minimum thickness of <0.5 mm. This is accomplished by the choice of a suitable partially crystalline polymer matrix while comparing non-polar polypropylene (PP) with polar polyvinylidene fluoride (PVDF) and a best suited filler nanomaterial by comparing different types of carbon nanotubes such as; branched, single-walled and multi-walled carbon nanotubes, which were added in only 2 wt %. Different types of interactions (polar-polar and CH-π and donor-acceptor) make b-MWCNT more dispersible in the PVDF matrix, which together with high crystallinity resulted in the best electrical conductivity and electromagnetic shielding ability of this composite. This investigation additionally conceals the issues related to the thickness of the shield material just by stacking individual thin nanocomposite layers containing different carbon nanotube (CNT) types with 0.3 mm thickness in a simple manner and finally achieves 99.999% shielding efficiency at just 0.9 mm thickness when using a suitable order of the different PVDF based nanocomposites
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Tuneable Dielectric Properties Derived from Nitrogen-Doped Carbon Nanotubes in PVDF-Based Nanocomposites
Nitrogen-doped multiwall carbon nanotubes (N-MWNTs) with different structures were synthesized by employing chemical vapor deposition and changing the argon/ethane/nitrogen gas precursor ratio and synthesis time, and broadband dielectric properties of their poly(vinylidene fluoride) (PVDF)-based nanocomposites were investigated. The structure, morphology, and electrical conductivity of synthesized N-MWNTs were assessed via Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy, and powder conductivity techniques. The melt compounded PVDF nanocomposites manifested significantly high real part of the permittivity (ϵ′) along with low dissipation factor (tan δϵ) in 0.1 kHz to 1 MHz frequency range, suggesting use as efficient charge-storage materials. Longer synthesis time resulted in enhanced carbon purity as well as higher thermal stability, determined via TGA analysis. The inherent electrical conductivity of N-MWNTs scaled with the carbon purity. The charge-storage ability of the developed PVDF nanocomposites was commensurate with the amount of the nitrogen heteroatom (i.e., self-polarization), carbon purity, and inherent electrical conductivity of N-MWNTs and increased with better dispersion of N-MWNTs in PVDF
Smart Textiles Coated with Eco-Friendly UV-Blocking Nanoparticles Derived from Natural Resources
Herein, eco-friendly iron titanate nanoparticles, FeTiO3 (FT), derived from natural resources (like ilmenite sand) were coated onto cotton fabrics (CF) to develop smart textile with enhanced UV-shielding property. The FT nanoparticles were dispersed in a polyurethane (PU) matrix, and the resulting nanocomposite was coated on CF. In addition, few sandwich architectures were designed by rationally stacking CF coated with PU and FT nanoparticles. The resulting sandwich structures blocked UV rays mainly by absorption. FT nanoparticles were comprehensively characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis, vibrating sample magnetometer, and thermogravimetric analysis. FT was suitably surface-functionalized to enhance the quality of dispersion in PU, thereby facilitating effective coating on CF. The latter was systematically evaluated by microscopic and spectroscopic techniques. In addition, flammability of the coated CF was evaluated and the char was assessed to gain insight into the fire-retardant properties. Interestingly, CF coated with FT exhibited a strong UV-shielding ability in sharp contrast to CF coated with PU. Further, the sandwich architecture consisting of CF with FT and PU resulted in an increase in the ultraviolet-protecting factor value to >50 compared to only PU-coated CF. Our results indicate that the sandwich structure holds excellent promise in the quest of designing smart textiles with enhanced UV shielding
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