Showing papers on "Polymer nanocomposite published in 2016"

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

Abstract: Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites

Abstract: Despite its widespread use in nanocomposites, the effect of embedding graphene in highly viscoelastic polymer matrices is not well understood. We added graphene to a lightly cross-linked polysilicone, often encountered as Silly Putty, changing its electromechanical properties substantially. The resulting nanocomposites display unusual electromechanical behavior, such as postdeformation temporal relaxation of electrical resistance and nonmonotonic changes in resistivity with strain. These phenomena are associated with the mobility of the nanosheets in the low-viscosity polymer matrix. By considering both the connectivity and mobility of the nanosheets, we developed a quantitative model that completely describes the electromechanical properties. These nanocomposites are sensitive electromechanical sensors with gauge factors >500 that can measure pulse, blood pressure, and even the impact associated with the footsteps of a small spider.

Polymer nanocomposites-A comparison between carbon nanotubes, graphene, and clay as nanofillers

Abstract: Nanofilled polymeric matrices have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review the processing of carbon nanotube, graphene, and clay montmorillonite platelet as potential nanofillers to form nanocomposites. The various functionalization techniques of modifying the nanofillers to enable interaction with polymers are summarized. The importance of filler dispersion in the polymeric matrix is highlighted. Finally, the challenges and future outlook for nanofilled polymeric composites are presented.

Giant Energy Density and Improved Discharge Efficiency of Solution-Processed Polymer Nanocomposites for Dielectric Energy Storage.

Abstract: Large-aspect-ratio composite nanofibers with interior hierarchical interfaces are employed to break the adverse coupling of electric displacement and breakdown strength in flexible poly(vinylidene fluoride-hexafluoropropylene) nanocomposite films, a small loading of 3 vol% BaTiO3@TiO2 nanofibers gives rise to the highestenergy density (≈31.2 J cm(-3)) ever achieved in polymer nanocomposites dielectrics.

Thermal exfoliation of hexagonal boron nitride for effective enhancements on thermal stability, flame retardancy and smoke suppression of epoxy resin nanocomposites via sol–gel process

Abstract: The structure of hexagonal boron nitride (h-BN) is similar to that of graphite before functionalization and exfoliation. For applications in polymer nanocomposites, chemical exfoliation is a more economically attractive route to few-layer h-BN nanosheets. A thermal oxidation process of h-BN powder could achieve large scale exfoliation and hydroxylated functionalization, as described in prior literature. In this report, hydroxylated h-BN (BNO) was prepared by heating h-BN under air, and then covalently incorporated into epoxy resin modified with (3-isocyanatopropyl)triethoxysilane to prepare epoxy resin (EP) nanocomposites by sol–gel process. The structure and morphology of BNO were well characterized. BNO was dispersed in the EP matrix with the form of mainly exfoliated and intercalated structures, and formed strong interfacial interaction with the matrix. Thermogravimetric analysis results revealed that BNO significantly improved thermal stability and thermal oxidative resistance of EP nanocomposites at high temperature. The char yield and the temperature at 50 wt% mass loss were increased and the maximum mass loss rate was remarkably reduced. Moreover, the addition of 3 wt% BNO led to extremely high Tg of EP nanocomposite, 42.7 °C higher than that of pure EP, due to improved crosslinking density and confinement effect of BNO sheets on the mobility of polymer networks. Cone calorimeter test results indicated that fire safety properties of EP nanocomposites were also enhanced by the addition of BNO, such as 53.1% reduction in peak heat release rate and 32.6% decrease in total heat release, and decreased release of smoke and toxic gases. The mechanism for enhanced fire retardancy is that thermally stable condensed barrier consisting of h-BN sheets and silicon dioxide for heat and mass transfer protects the matrix from further combustion.

Sandwich-structured polymer nanocomposites with high energy density and great charge–discharge efficiency at elevated temperatures

Abstract: The demand for a new generation of high-temperature dielectric materials toward capacitive energy storage has been driven by the rise of high-power applications such as electric vehicles, aircraft, and pulsed power systems where the power electronics are exposed to elevated temperatures. Polymer dielectrics are characterized by being lightweight, and their scalability, mechanical flexibility, high dielectric strength, and great reliability, but they are limited to relatively low operating temperatures. The existing polymer nanocomposite-based dielectrics with a limited energy density at high temperatures also present a major barrier to achieving significant reductions in size and weight of energy devices. Here we report the sandwich structures as an efficient route to high-temperature dielectric polymer nanocomposites that simultaneously possess high dielectric constant and low dielectric loss. In contrast to the conventional single-layer configuration, the rationally designed sandwich-structured polymer nanocomposites are capable of integrating the complementary properties of spatially organized multicomponents in a synergistic fashion to raise dielectric constant, and subsequently greatly improve discharged energy densities while retaining low loss and high charge-discharge efficiency at elevated temperatures. At 150 °C and 200 MV m(-1), an operating condition toward electric vehicle applications, the sandwich-structured polymer nanocomposites outperform the state-of-the-art polymer-based dielectrics in terms of energy density, power density, charge-discharge efficiency, and cyclability. The excellent dielectric and capacitive properties of the polymer nanocomposites may pave a way for widespread applications in modern electronics and power modules where harsh operating conditions are present.

Study of nanoparticles aggregation/agglomeration in polymer particulate nanocomposites by mechanical properties

Abstract: A simple approach is described to study the aggregation/agglomeration details in polymer nanocomposites reinforced with spherical nanoparticles. The suggested methodology for mechanical properties can offer the aggregation/agglomeration level as a function of different parameters. In addition, the effective volume fraction of agglomerated nanoparticles in nanocomposite samples ( ϕ agg ) is determined by the present technique. The calculated results for various samples express that the aggregation/agglomeration of nanoparticles is occurred in all reported nanocomposites. Also, both aggregate/agglomerate and nanofiller diameters play important roles in aggregation/agglomeration level of samples. The aggregation/agglomeration extent increases by addition of nanofiller content and reduction of nanofiller size. Moreover, the aggregation/agglomeration decreases the effectiveness of nanoparticles in polymer matrix, which lastly results in the poor properties of samples.

Mechanical, Thermal, and Electrical Properties of Graphene-Epoxy Nanocomposites—A Review

Abstract: Monolithic epoxy, because of its brittleness, cannot prevent crack propagation and is vulnerable to fracture. However, it is well established that when reinforced—especially by nano-fillers, such as metallic oxides, clays, carbon nanotubes, and other carbonaceous materials—its ability to withstand crack propagation is propitiously improved. Among various nano-fillers, graphene has recently been employed as reinforcement in epoxy to enhance the fracture related properties of the produced epoxy–graphene nanocomposites. In this review, mechanical, thermal, and electrical properties of graphene reinforced epoxy nanocomposites will be correlated with the topographical features, morphology, weight fraction, dispersion state, and surface functionalization of graphene. The factors in which contrasting results were reported in the literature are highlighted, such as the influence of graphene on the mechanical properties of epoxy nanocomposites. Furthermore, the challenges to achieving the desired performance of polymer nanocomposites are also suggested throughout the article.

Next-generation polymer nanocomposite-based electrochemical sensors and biosensors: A review

Abstract: Due to their unique and fascinating properties, polymer nanocomposites (PNCs) have been extensively studied in recent years. PNCs can be synthesized in several different nanoscale forms with minimal effort, thus allowing the fabrication of various novel chemical and biological sensors. This review covers recent applications based on PNCs for the fabrication of electrochemical sensors, biosensors, including DNA biosensors, immunosensors, and aptamer sensors. To improve the sensor performance, nanocomposites have been reported in various combinations such as conductive polymers with graphene (Grp), carbon nanotubes (CNTs), and metal nanoparticles, which endow high electrical conductivity, effective surface area, and fast electron transfer rate.

Reasons and remedies for the agglomeration of multilayered graphene and carbon nanotubes in polymers

Abstract: One of the main issues in the production of polymer nanocomposites is the dispersion state of filler as multilayered graphene (MLG) and carbon nanotubes (CNTs) tend to agglomerate due to van der Waals forces. The agglomeration can be avoided by using organic solvents, selecting suitable dispersion and production methods, and functionalizing the fillers. Another proposed method is the use of hybrid fillers as synergistic effects can cause an improvement in the dispersion state of the fillers. In this review article, various aspects of each process that can help avoid filler agglomeration and improve dispersion state are discussed in detail. This review article would be helpful for both current and prospective researchers in the field of MLG- and CNT-based polymer nanocomposites to achieve maximum enhancement in mechanical, thermal, and electrical properties of produced polymer nanocomposites.

Polymer brush synthesis on surface modified carbon nanotubes via in situ emulsion polymerization

Abstract: In situ emulsion polymerization was employed for synthesizing carbon nanotube (CNT) composites in a colloidal system with poly(styrene) or PS to form nanostructured brush. CNTs were initially functionalized with oleic acid, followed by silanization with (3-aminopropyl) triethoxysilane to impart cross-linking properties. Styrene monomers were efficiently grafted to surface modified CNT via emulsion polymerization with variable CNT concentrations. FTIR analyses of the functionalized CNT and PS/CNT composites confirmed the bond formation and effectiveness of the developed experimental method. X-ray photoelectron spectroscopy confirmed the presence of the desired bonds and the composition of the composites. Structural properties of the composites characterized by TEM confirmed excellent deagglomeration and dispersion of CNTs in PS/CNT composite. Thermal characteristics from TGA and DSC data showed enhanced properties for the nanocomposites as a function of the CNT content. BET measurements indicated significant improvements in surface area and pore volume with enhancements in gas sorption for the polymer nanocomposites.

Facile Exfoliation and Noncovalent Superacid Functionalization of Boron Nitride Nanosheets and Their Use for Highly Thermally Conductive and Electrically Insulating Polymer Nanocomposites.

Abstract: There is an increasing demand for highly thermally conductive and electrically insulating polymer materials for next-generation electronic devices, power systems, and communication equipment. Boron nitride nanosheets (BNNSs) are insulating materials with extremely high thermal conductivity. However, BNNSs suffer from the lack of facile and low-cost methods for producing large volumes of BNNSs, and extremely low through-plane thermal conductivities of BNNS/polymer composites as compared to the in-plane thermal conductivities. Herein, highly soluble, noncovalently functionalized boron nitride nanosheets (NF-BNNSs) with chlorosulfonic acid (CSA) were prepared by extremely facile and low-cost direct exfoliation of hexagonal boron nitrides (h-BNs), and acted as excellent nanofillers for dramatically improving both in- and through-plane thermal conductivities of insulating polymers. CSA is a cheap and versatile superacid with a large production volume. CSA showed strong physical adsorption on h-BN surfaces, giv...

Excellent energy density of polymer nanocomposites containing BaTiO3@Al2O3 nanofibers induced by moderate interfacial area

Abstract: Inorganic/polymer nanocomposites, using one-dimensional (1D) core–shell structure BaTiO3@Al2O3 nanofibers (BT@Al2O3 nfs) as fillers and poly(vinylidene fluoride) (PVDF) as the polymer matrix, have been prepared. The core–shell structure BT@Al2O3 nfs have been synthesized via coaxial electrospinning. The breakdown strength (Eb) and discharged energy density of the nanocomposites can be significantly improved by creating an insulating Al2O3 shell layer with moderate dielectric constant on the surfaces of BT nanofibers to form a moderate interfacial area. The Al2O3 shell layer could effectively confine the mobility of charge carriers, which reduces energy loss by reducing the Maxwell–Wagner–Sillars (MWS) interfacial polarization and space charge polarization between the fillers and the polymer matrix. As a result, the nanocomposite films filled with 5 vol% BT@Al2O3 nfs exhibit a excellent discharge energy density of 12.18 J cm−3 at 400 MV m−1, which is ≈254% over bare PVDF (4.8 J cm−3 at 350 MV m−1) and ≈1015% greater than the biaxially oriented polypropylenes (BOPP) (≈1.2 J cm−3 at 640 MV m−1). The work here indicates that this promising state-of-the-art method of preparing high energy density nanocomposites can be used in the next generation of dielectric capacitors.

Controlling Interfacial Dynamics: Covalent Bonding versus Physical Adsorption in Polymer Nanocomposites

Abstract: It is generally believed that the strength of the polymer–nanoparticle interaction controls the modification of near-interface segmental mobility in polymer nanocomposites (PNCs). However, little is known about the effect of covalent bonding on the segmental dynamics and glass transition of matrix-free polymer-grafted nanoparticles (PGNs), especially when compared to PNCs. In this article, we directly compare the static and dynamic properties of poly(2-vinylpyridine)/silica-based nanocomposites with polymer chains either physically adsorbed (PNCs) or covalently bonded (PGNs) to identical silica nanoparticles (RNP = 12.5 nm) for three different molecular weight (MW) systems. Interestingly, when the MW of the matrix is as low as 6 kg/mol (RNP/Rg = 5.4) or as high as 140 kg/mol (RNP/Rg= 1.13), both small-angle X-ray scattering and broadband dielectric spectroscopy show similar static and dynamic properties for PNCs and PGNs. However, for the intermediate MW of 18 kg/mol (RNP/Rg = 3.16), the difference betwee...

Recent advances in CNT/graphene based thermoelectric polymer nanocomposite: A proficient move towards waste energy harvesting

Abstract: Carbon nano tube (CNT)/graphene filled organic composites have great potential for making cheaper thermoelectric materials towards their gear up for applications in energy harvesting due to their low cost, low density, facile routes of preparations, versatile processability and low thermal conductivity. These properties make them superior compared to previously reported hybrid alloys. Now a day׳s CNT and graphene are most frequently used nanofillers due to their unique shape and characteristics such as superconductivity, light weight, high stiffness and axial strength. Moreover, to achieve superior dispersion and properties of composites, various functionalizations on the graphene and CNT have been accomplished by various research groups. Foremost objective of this paper is to highlight the recent research advances on CNT and graphene filled thermoelectric (TE) materials for the replacement of inorganic semiconductors. Fundamentally, for polymer composite based thermoplastic (TP) materials, a thermally nonconductive but electrically connected nano-structured network should be established.

High energy density of polymer nanocomposites at a low electric field induced by modulation of their topological-structure

Abstract: Polymer nanocomposite dielectrics are of critical importance for a number of electrical and electronic applications. It is highly desirable to achieve high energy density at a low electric field. In this contribution, PVDF-based (or PVDF–TrFE–CFE based) nanocomposite films filled with BaTiO3@TiO2 nanofibers are cast from solutions. Topological-structure modulated polymer nanocomposites are assembled layer-by-layer with the as-cast films via a hot-pressing process. Modulation of the topological-structure induces substantial redistribution of the local electric field among the constituent layers, giving rise to enhanced electric polarization at a low electric field and increased breakdown strength. These synergistic effects lead to an ultrahigh energy density of ∼12.5 J cm−3 and a high discharge efficiency of ∼70% at 350 kV mm−1. High energy density at a low electric field is thus achieved by modulating the topological structure of polymer dielectric nanocomposites, which is of critical significance to make dielectric nanocomposites viable energy storage devices.

Unraveling the Mechanism of Nanoscale Mechanical Reinforcement in Glassy Polymer Nanocomposites.

Abstract: The mechanical reinforcement of polymer nanocomposites (PNCs) above the glass transition temperature, Tg, has been extensively studied. However, not much is known about the origin of this effect below Tg. In this Letter, we unravel the mechanism of PNC reinforcement within the glassy state by directly probing nanoscale mechanical properties with atomic force microscopy and macroscopic properties with Brillouin light scattering. Our results unambiguously show that the “glassy” Young’s modulus in the interfacial polymer layer of PNCs is two-times higher than in the bulk polymer, which results in significant reinforcement below Tg. We ascribe this phenomenon to a high stretching of the chains within the interfacial layer. Since the interfacial chain packing is essentially temperature independent, these findings provide a new insight into the mechanical reinforcement of PNCs also above Tg.

Unexpected Molecular Weight Effect in Polymer Nanocomposites.

Abstract: The properties of the interfacial layer between the polymer matrix and nanoparticles largely determine the macroscopic properties of polymer nanocomposites (PNCs). Although the static thickness of the interfacial layer was found to increase with the molecular weight (MW), the influence of MW on segmental relaxation and the glass transition in this layer remains to be explored. In this Letter, we show an unexpected MW dependence of the interfacial properties in PNC with attractive polymer-nanoparticle interactions: the thickness of the interfacial layer with hindered segmental relaxation decreases as MW increases, in sharp contrast to theoretical predictions. Further analyses reveal a reduction in mass density of the interfacial layer with increasing MW, which can elucidate these unexpected dynamic effects. Our observations call for a significant revision of the current understandings of PNCs and suggest interesting ways to tailor their properties.

Enhanced electric displacement induces large energy density in polymer nanocomposites containing core–shell structured BaTiO3@TiO2 nanofibers

Abstract: High energy density polymer nanocomposites are quite promising for film capacitors and many other electronic devices. In this study, the promising strategy is to increase the electric displacement in high breakdown strength nanocomposites with low loading nanofillers. The core–shell structured barium titanate@titanium dioxide nanofiber (BTO@TO-nf) reported herein is designed based on interfacial engineering and prepared using coaxial electrospinning. In the PVDF nanocomposites containing the core–shell nanofibers, the dielectric permittivity as well as the electric displacement increase significantly, due to the additional polarization induced by the charge shifting in the interfacial zone between BTO on the inside and TO on the outside, which contributes significantly to the electric displacement. In addition, the breakdown strength of the nanocomposite is maintained through the charge shifting being limited to the interfacial zone so it cannot form a percolation path in the matrix. A large discharged energy density of ca. 10.94 J cm−3 is achieved at a field of 360 kV mm−1 for the nanocomposite film with 3% volume fraction of BTO@TO-nf, which is higher than those of the referenced PVDF nanocomposites under the same electric field. The present study demonstrates the advantages of the core–shell structured nanofibers in improving the dielectric properties and provides a new way to enhance the energy density of polymer nanocomposites.

Modeling of Polymer Structure and Conformations in Polymer Nanocomposites from Atomistic to Mesoscale: A Review

Abstract: Over the past two decades polymer nanocomposites have received tremendous interest from industry and academia due to their advanced properties comparative to polymer blends. Many computational studies have revealed that the macroscopic properties of polymer nanocomposites depend strongly on the microscopic polymer structure and conformations. In this article we review computer simulation studies of the fundamental problem of homopolymers structure and dimensions in nanocomposites containing bare or grafted spherical or rod nanoparticles. Experimentally, there is controversy over whether the addition of nanoparticles in a polymer matrix can perturb the polymer chains.

Surface-modified Ba(Zr0.3Ti0.7)O3 nanofibers by polyvinylpyrrolidone filler for poly(vinylidene fluoride) composites with enhanced dielectric constant and energy storage density.

Abstract: Ferroelectric-relaxor behavior of Ba(Zr03Ti07)O3 nanofibers (BZT NF) with a large aspect ratio were prepared via electrospinning and surface modified by PVP as dielectric fillers The nanocomposite flexible films based on surface modified BZT NF and polyvinylidene fluoride (PVDF) were fabricated via a solution casting The results show that the surface-modified BZT NF fillers are highly dispersed and well integrated in the PVDF nanocomposites The nanocomposites exhibit enhanced dielectric constant and reduced loss tangents at a low volume fraction of surface-modified BZT NF The polymer nanocomposites maintain a relatively high breakdown strength, which is favorable for enhancing energy storage density in the nanocomposites The nanocomposite containing of 25 vol % of PVP modified BZT NF exhibits energy density as high as 63 J/cm3 at 3800 kV/cm, which is more than doubled that of the pure PVDF of 28 J/cm3 at 4000 kV/cm Such significant enhancement could be attributed to the combined effects of the surface modification and large aspect ratio of the BZT NF This work may provide a route for using the surface modified ferroelectric-relaxor behavior of ceramic nanofibers to enhance the dielectric energy density in ceramic-polymer nanocomposites

Linking traps to dielectric breakdown through charge dynamics for polymer nanocomposites

Abstract: Polymer nanocomposites can change the density and/or energy of traps, suppress the accumulation of space charges, and enhance dielectric breakdown strength. It is of interest to reveal the influencing mechanism of trap properties on the dielectric breakdown of polymer nanocomposites. Results of thermally stimulated depolarization current and surface potential decay were reviewed, showing that incorporating a small amount of nanoparticles into a polymer can increase the density and/or energy of deep traps. Then, the relation between traps and dc breakdown field of several polymer nanocomposites were analyzed. It was found that the increase in the density and energy of deep traps contributes to the improved dielectric breakdown performance. The modifications of traps by nanoparticles and surface treatments affect the charge dynamics in the bulk of polymer nanocomposites. Then, the accumulation of space charges, the distortion of electric field, and the energy gain of free carriers are regulated to improve the performance of dielectric breakdown.

Macromolecule and Particle Dynamics in Confined Media

Abstract: Dynamic properties play an important role in designing functional polymer nanocomposites, impacting molecular transport and phase separation kinetics. When nanoparticle (NP) size is comparable to polymer chain size, segmental relaxations may be influenced by changes in chain conformations and packing at the polymer/NP interface. Following the reptation model, these changes can perturb the longest relaxation time, in particular, the center-of-mass (COM) dynamics of polymer chains in entangled melts. This Perspective focuses on unsolved issues in polymer COM diffusion and local dynamics and segmental motions in the presence of NPs. The article introduces the effect of NP size, shape, surface modification, and enthalpic interactions on polymer diffusion and further relates dynamic studies in PNCs to macromolecular transport in bio-related systems and nanopores. Studies of local dynamics also provide insights into how entanglement density, monomeric friction, and chain conformation are influenced by NPs and h...