Showing papers on "Polymer nanocomposite published in 2018"

Thermal conductivity of polymers and polymer nanocomposites

Abstract: Polymers are widely used in industry and in our daily life because of their diverse functionality, light weight, low cost and excellent chemical stability. However, on some applications such as heat exchangers and electronic packaging, the low thermal conductivity of polymers is one of the major technological barriers. Enhancing the thermal conductivity of polymers is important for these applications and has become a very active research topic over the past two decades. In this review article, we aim to: 1). systematically summarize the molecular level understanding on the thermal transport mechanisms in polymers in terms of polymer morphology, chain structure and inter-chain coupling; 2). highlight the rationales in the recent efforts in enhancing the thermal conductivity of nanostructured polymers and polymer nanocomposites. Finally, we outline the main advances, challenges and outlooks for highly thermal-conductive polymer and polymer nanocomposites.

Methods for Synthesis of Nanoparticles and Fabrication of Nanocomposites

Abstract: This chapter deals with the synthesis of nanoparticles, and the synthesis and fabrication of nanocomposites—metal, ceramic, and polymeric. Various methods used to synthesize nanoparticles, such as coprecipitation, hydrothermal synthesis, inert gas condensation, ion sputtering scattering, microemulsion, microwave, pulse laser ablation, sol-gel, sonochemical, spark discharge, template synthesis, and biological synthesis, will be described. The synthesis of metal nanocomposites includes spray pyrolysis, liquid infiltration, the rapid solidification process, high-energy ball milling, chemical vapor deposition, physical vapor deposition, and chemical processes—sol-gel and colloidal. The synthesis of ceramic nanocomposites includes the powder process, polymer precursor process, and the sol-gel process. Finally, the fabrication of polymer nanocomposites includes intercalation, in situ intercalative polymerization, melt intercalation, template synthesis, mixing, in situ polymerization, and the sol-gel process. A summary with perspective concludes the chapter.

Effects of Size and Aggregation/Agglomeration of Nanoparticles on the Interfacial/Interphase Properties and Tensile Strength of Polymer Nanocomposites

Abstract: In this study, several simple equations are suggested to investigate the effects of size and density on the number, surface area, stiffening efficiency, and specific surface area of nanoparticles in polymer nanocomposites. In addition, the roles of nanoparticle size and interphase thickness in the interfacial/interphase properties and tensile strength of nanocomposites are explained by various equations. The aggregates/agglomerates of nanoparticles are also assumed as large particles in nanocomposites, and their influences on the nanoparticle characteristics, interface/interphase properties, and tensile strength are discussed. The small size advantageously affects the number, surface area, stiffening efficiency, and specific surface area of nanoparticles. Only 2 g of isolated and well-dispersed nanoparticles with radius of 10 nm (R = 10 nm) and density of 2 g/cm3 produce the significant interfacial area of 250 m2 with polymer matrix. Moreover, only a thick interphase cannot produce high interfacial/interphase parameters and significant mechanical properties in nanocomposites because the filler size and aggregates/agglomerates also control these terms. It is found that a thick interphase (t = 25 nm) surrounding the big nanoparticles (R = 50 nm) only improves the B interphase parameter to about 4, while B = 13 is obtained by the smallest nanoparticles and the thickest interphase.

A Scalable, High-Throughput, and Environmentally Benign Approach to Polymer Dielectrics Exhibiting Significantly Improved Capacitive Performance at High Temperatures

Abstract: High-temperature capability is critical for polymer dielectrics in the next-generation capacitors demanded in harsh-environment electronics and electrical-power applications. It is well recognized that the energy-storage capabilities of dielectrics are degraded drastically with increasing temperature due to the exponential increase of conduction loss. Here, a general and scalable method to enable significant improvement of the high-temperature capacitive performance of the current polymer dielectrics is reported. The high-temperature capacitive properties in terms of discharged energy density and the charge-discharge efficiency of the polymer films coated with SiO2 via plasma-enhanced chemical vapor deposition significantly outperform the neat polymers and rival or surpass the state-of-the-art high-temperature polymer nanocomposites that are prepared by tedious and low-throughput methods. Moreover, the surface modification of the dielectric films is carried out in conjunction with fast-throughput roll-to-roll processing under ambient conditions. The entire fabrication process neither involves any toxic chemicals nor generates any hazardous by-products. The integration of excellent performance, versatility, high productivity, low cost, and environmental friendliness in the present method offers an unprecedented opportunity for the development of scalable high-temperature polymer dielectrics.

High-Throughput Phase-Field Design of High-Energy-Density Polymer Nanocomposites.

Abstract: Understanding the dielectric breakdown behavior of polymer nanocomposites is crucial to the design of high-energy-density dielectric materials with reliable performances. It is however challenging to predict the breakdown behavior due to the complicated factors involved in this highly nonequilibrium process. In this work, a comprehensive phase-field model is developed to investigate the breakdown behavior of polymer nanocomposites under electrostatic stimuli. It is found that the breakdown strength and path significantly depend on the microstructure of the nanocomposite. The predicted breakdown strengths for polymer nanocomposites with specific microstructures agree with existing experimental measurements. Using this phase-field model, a high throughput calculation is performed to seek the optimal microstructure. Based on the high-throughput calculation, a sandwich microstructure for PVDF-BaTiO3 nanocomposite is designed, where the upper and lower layers are filled with parallel nanosheets and the middle layer is filled with vertical nanofibers. It has an enhanced energy density of 2.44 times that of the pure PVDF polymer. The present work provides a computational approach for understanding the electrostatic breakdown, and it is expected to stimulate future experimental efforts on synthesizing polymer nanocomposites with novel microstructures to achieve high performances.

Stretchable Electrospun PVDF-HFP/Co-ZnO Nanofibers as Piezoelectric Nanogenerators.

Abstract: Herein, we investigate the morphology, structure and piezoelectric performances of neat polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) and PVDF-HFP/Co-ZnO nanofibers, fabricated by electrospinning. An increase in the amount of crystalline β-phase of PVDF-HFP has been observed with the increase in Co-doped ZnO nanofiller concentration in the PVDF-HFP matrix. The dielectric constants of the neat PVDF-HFP and PVDF-HFP/2 wt.% Co-ZnO nanofibers are derived as 8 and 38 respectively. The flexible nanogenerator manipulated from the polymer nanocomposite (PVDF-HFP/Co-ZnO) exhibits an output voltage as high as 2.8 V compared with the neat PVDF-HFP sample (~120 mV). These results indicate that the investigated nanocomposite is appropriate for fabricating various flexible and wearable self-powered electrical devices and systems.

Polymer Nanocomposites with Ultrahigh Energy Density and High Discharge Efficiency by Modulating their Nanostructures in Three Dimensions.

Abstract: Manipulating microstructures of composites in three dimensions has been a long standing challenge. An approach is proposed and demonstrated to fabricate artificial nanocomposites by controlling the 3D distribution and orientation of oxide nanoparticles in a polymer matrix. In addition to possessing much enhanced mechanical properties, these nanocomposites can sustain extremely high voltages up to ≈10 kV, exhibiting high dielectric breakdown strength and low leakage current. These nanocomposites show great promise in resolving the paradox between dielectric constant and breakdown strength, leading to ultrahigh electrical energy density (over 2000% higher than that of the bench-mark polymer dielectrics) and discharge efficiency. This approach opens up a new avenue for the design and modulation of nanocomposites. It is adaptable to the roll-to-roll fabrication process and could be employed as a general technique for the mass production of composites with intricate nanostructures, which is otherwise not possible using conventional polymer processing techniques.

Surface modification of hexagonal boron nitride nanomaterials: a review

Abstract: Hexagonal boron nitride (h-BN) nanomaterials, such as boron nitride nanotubes, boron nitride nanofibers, and boron nitride nanosheets, are among the most promising inorganic nanomaterials in recent years. Their unique properties, including high mechanical stiffness, wide band gap, excellent thermal conductivity, and thermal stability, suggest many potential applications in various engineering fields. In particular, h-BN nanomaterials have been widely used as functional fillers to fabricate high-performance polymer nanocomposites. Like other nanomaterials, prior to their utilization in nanocomposites, surface modification of h-BNs is often necessary in order to prevent their strong tendency to aggregate, and to improve their dispersion and interfacial properties in polymer nanocomposites. However, the high chemical inertness and resistance to oxidation of h-BNs make it rather difficult to functionalize h-BNs. The methods frequently used to oxidize graphitic carbon nanomaterials are not quite successful on h-BNs. Therefore, many novel approaches have been studied to modify h-BN nanostructures. In this review, different surface modification strategies were discussed including various covalent and non-covalent surface modification strategies through wet or dry chemical routes. Meanwhile, the effects of these surface modification methods on the resulting material structures and properties were also reviewed. At last, a number of theoretical studies on the reactivity of h-BNs with different chemical agents have been conducted to explore new surface modification routes, which were also addressed in this review.

An Overview of Electrically Conductive Polymer Nanocomposites toward Electromagnetic Interference Shielding

Abstract: A comprehensive overview of the up-to-date research activities targeting electromagnetic interference (EMI) shielding is provided, focusing on the multifunctional polymer nanocomposites (PNCs) reinforced with a variety of conductive fillers. The unique dielectric, magnetic and other physicochemical properties derived from certain morphology-, composition-, and loading-controlled nanostructures for EMI shielding behaviors are elaborated. The conductive fillers including three different categories: carbon, metals, and conductive polymers in the EMI shielding PNCs are discussed together with their synergistic effects on enhancing the EMI shielding property. The enhanced electromagnetic interference shielding effectiveness and mechanisms are discussed with detailed examples and are envisioned to provide rational design of next generation lightweight EMI shielding materials.

Plasmonic polymer nanocomposites

Abstract: The optical properties of metal nanoparticles, particularly their localized surface plasmon effects, are well established. These plasmonic nanoparticles can respond to their surroundings or even influence the optical processes (for example, absorption, fluorescence and Raman scattering) of molecules located at their surface. As a result, plasmonic nanoparticles have been developed for multiple purposes, ranging from the detection of chemicals and biological molecules to light-harvesting enhancement in solar cells. By dispersing the nanoparticles in polymers and creating a hybrid material, the robustness, responsiveness and flexibility of the system are enhanced while preserving the intrinsic properties of the nanoparticles. In this Review, we discuss the fabrication and applications of plasmonic polymer nanocomposites, focusing on applications in optical data storage, sensing and imaging and photothermal gels for in vivo therapy. Within the nanocomposites, the nanoporosity of the matrix, the overall mechanical stability and the dispersion of the nanoparticles are important parameters for achieving the best performance. In the future, translation of these materials into commercial products rests on the ability to scale up the production of plasmonic polymer nanocomposites with tailored optical features.

Three-dimensional graphene-based polymer nanocomposites: preparation, properties and applications

Abstract: Motivated by the unique structure and outstanding properties of graphene, three-dimensional (3D) graphene-based polymer nanocomposites (3D-GPNCs) are considered as new generation materials for various multi-functional applications. This review presents an overview of the preparation, properties and applications of 3D-GPNCs. Three main approaches for fabricating 3D-GPNCs, namely 3D graphene based template, polymer particle/foam template, and organic molecule cross-linked graphene, are introduced. A thorough investigation and comparison of the mechanical, electrical and thermal properties of 3D-GPNCs are performed and discussed to understand their structure–property relationship. Various potential applications of 3D-GPNCs, including energy storage and conversion, electromagnetic interference shielding, oil/water separation, and sensors, are reviewed. Finally, the current challenges and outlook of these emerging 3D-GPNC materials are also discussed.

High-energy-density with polymer nanocomposites containing of SrTiO3 nanofibers for capacitor application

Abstract: Inorganic/polymer nanocomposite films have attracted pronounced attention for electric energy storage applications since their high power energy density and fast charge-discharge ability. In this work, the flexible nanocomposite films composed by the paraelectric SrTiO3 nanofibers (ST NFs) and poly(vinylidene fluoride) (PVDF) were prepared by a solution cast method. The ST NFs, synthesized by an electrospinning method, were coated with a dense and robust dopamine layer which could effectively improve the filler-matrix distributional homogeneity and compatibility. The composite film with an optimized filler content illustrates a high discharge energy density of 9.12 J/cm3 at 360 MV/m, which is about 625% over the biaxially oriented polypropylenes (BOPP) (1.2 J/cm3 at 640 MV/m). Moreover, the composite film shows a superior power density of 2.31 MW/cm3 and ultra-fast discharge speed of 178 ns. Therefore, the present approach might be extended to the fabrication of similar polymeric nanocomposites for high-performance capacitor energy storage devices.

Surface modification and drug delivery applications of MoS 2 nanosheets with polymers through the combination of mussel inspired chemistry and SET-LRP

Abstract: Mussel inspired chemistry is a promising surface modification tool, which has attracted great research attention for different applications owing to its universality and interest properties. In this work, a rather simple and efficient method for the surface modification of MoS2 nanosheets with copolymers was achieved through the combination of mussel inspired chemistry and single-electron transfer living radical polymerization (SET-LRP) using 2-methacryloyloxyethyl phosphorylcholine (MPC) and itaconic acid (IA) as the monomers. The obtained MoS2-PDA-poly(MPC-IA) nanocomposites were ascertained by a series of characterization techniques, such as nuclear magnetic resonance spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. Moreover, the MoS2-PDA-poly(MPC-IA) nanocomposites showed enhanced dispersbility and great biocompatibility. The results implied that the MoS2-PDA-poly(MPC-IA) nanocomposites showed great potential in the field of biomedical science. In this work, the drug loading capability and controlled drug release behavior towards CDDP have been investigated. The drug loading in MoS2-PDA-poly(MPC-IA) composites is as high as 55.26%. All of these above results suggested that the combination of mussel inspired chemistry and SET-LRP is a facile and efficient strategy for fabrication of MoS2 based polymer nanocomposites with great potential application in biomedical fields.

Decorating TiO2 Nanowires with BaTiO3 Nanoparticles: A New Approach Leading to Substantially Enhanced Energy Storage Capability of High-k Polymer Nanocomposites

Abstract: The urgent demand of high energy density and high power density devices has triggered significant interest in high dielectric constant (high-k) flexible nanocomposites comprising dielectric polymer and high-k inorganic nanofiller. However, the large electrical mismatch between polymer and nanofiller usually leads to earlier electric failure of the nanocomposites, resulting in an undesirable decrease of electrical energy storage capability. A few studies show that the introduction of moderate-k shell onto a high-k nanofiller surface can decrease the dielectric constant mismatch, and thus, the corresponding nanocomposites can withstand high electric field. Unfortunately, the low apparent dielectric enhancement of the nanocomposites and high electrical conductivity mismatch between matrix and nanofiller still result in low energy density and low efficiency. In this study, it is demonstrated that encapsulating moderate-k nanofiller with high-k but low electrical conductivity shell is effective to significantl...

Cellulose nanomaterials as green nanoreinforcements for polymer nanocomposites

Abstract: Unexpected and attractive properties can be observed when decreasing the size of a material down to the nanoscale. Cellulose is no exception to the rule. In addition, the highly reactive surface of cellulose resulting from the high density of hydroxyl groups is exacerbated at this scale. Different forms of cellulose nanomaterials, resulting from a top-down deconstruction strategy (cellulose nanocrystals, cellulose nanofibrils) or bottom-up strategy (bacterial cellulose), are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, the basis for low-density foams, additives in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic and medical products. This paper focuses on the use of cellulose nanomaterials as a filler for the preparation of polymer nanocomposites. Impressive mechanical properties can be obtained for these materials. They obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. The emphasis is on the melt processing of such nanocomposite materials, which has not yet been properly resolved and remains a challenge.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Enhanced Thermal Conductivity of Graphene Nanoplatelet-Polymer Nanocomposites Fabricated via Supercritical Fluid-Assisted in Situ Exfoliation.

Abstract: As electronic devices become increasingly miniaturized, their thermal management becomes critical. Efficient heat dissipation guarantees their optimal performance and service life. Graphene nanoplatelets (GnPs) have excellent thermal properties that show promise for use in fabricating commercial polymer nanocomposites with high thermal conductivity. Herein, an industrially viable technique for manufacturing a new class of lightweight GnP-polymer nanocomposites with high thermal conductivity is presented. Using this method, GnP-high-density polyethylene (HDPE) nanocomposites with a microcellular structure are fabricated by melt mixing, which is followed by supercritical fluid (SCF) treatment and injection molding foaming, which adds an extra layer of design flexibility. Thus, the microstructure is tailored within the nanocomposites and this improves their thermal conductivity. Therefore, the SCF-treated HDPE 17.6 vol % GnP microcellular nanocomposites have a solid-phase thermal conductivity of 4.13 ± 0.12 W m-1 K-1. This value far exceeds that of their regular injection-molded counterparts (2.09 ± 0.03 W m-1 K-1) and those reported in the literature. This dramatic improvement results from in situ GnPs' exfoliation and dispersion, and from an elevated level of random orientation and interconnectivity. Thus, this technique provides a novel approach to the development of microscopically tailored structures for the production of lighter and more thermally conductive heat sinks for next generations of miniaturized electronic devices.

A three-dimensional multilayer graphene web for polymer nanocomposites with exceptional transport properties and fracture resistance

Abstract: Small amounts of two-dimensional (2D) graphene sheets are usually added into a polymer matrix to fabricate nanocomposites with improved mechanical and functional properties. Further enhancements of these properties beyond those of ordinary nanocomposites require much higher loadings of well-dispersed fillers, preferably in the form of an interconnected network with the preferential orientation along the direction of interest. However, the assembly of 2D fillers to form such a three-dimensional (3D) network remains a formidable task. Herein, a totally new approach is developed to fabricate a high-density 3D multilayer graphene web with interconnected, in-plane oriented graphene struts based on the versatile chemical vapor deposition technique. The continuous high-quality graphene network within the epoxy composites leads to exceptional electrical and thermal conductivities of 50 S cm−1 and 8.8 Wm−1 K−1, respectively. The high filler loading of 8.3 wt% also gives rise to a remarkable fracture toughness of 2.18 MPa m1/2, well over 100% enhancement over the neat epoxy. The simultaneous achievements of both remarkable transport properties and fracture toughness at these levels by an identical nanocomposite are unprecedented and have never been reported previously. The combination of unrivalled electrical and thermal conductivities with extraordinary fracture resistance offers the composites unique opportunities for multi-functional applications.

Enhanced β-phase in PVDF polymer nanocomposite and its application for nanogenerator

Abstract: Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β-phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF-ZnO nanocomposite films by using X-ray diffractometer, Fourier transform infrared spectroscopy, and polarization-electric field loop measurements supports the enhancement of β-phase in the flexible nanocomposite polymer films. The piezoelectric constant (d33) of the PVDF-ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open-circuit voltage ~1.81 V and short-circuit current of 0.57 μA are obtained for 15 wt% ZnO-loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm2 with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small-scale electronic devices. This enhanced piezoresponse of the PVDF-ZnO nanocomposite film-based nanogenerators attributed to the enhancement of electroactive β-phase and enhanced d33 value in PVDF with the addition of ZnO nanorods.

Effects of octadecylamine functionalization of carbon nanotubes on dispersion, polarity, and mechanical properties of CNT/HDPE nanocomposites

Abstract: Homogeneous dispersion of carbon nanotubes (CNTs) in polymers has significantly improved their processing and application as nanomaterials. Generally, CNTs tend to agglomerate due to their high aspect ratios and strong van der Waals interaction. Surface functionalization appears to be a solution to this problem. This study presents a controlled dispersion of carbon nanotubes in polyethylene through surface modification using a mixture of concentrated acid and octadecylamine (ODA). CNTs were characterized by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, and transmission electron microscopy. The results confirmed that carboxyl and alkane groups were successfully introduced on CNT surfaces. The acid- and amine-functionalized carbon nanotubes were dispersed in four solvents with different polarities (water, ethanol, acetone, and xylene) to correlate the degree of dispersion of CNT with their polarity. The results showed that CNT dispersion stability strongly depends on solvent and carbon nanotube polarities after the functionalization step. The nanohardness and tensile tests showed that the addition of CNTs, especially the functionalized with ODA, leaded the polymer harder, increasing its Young’s modulus and tensile strength. However, its toughness and deformation capacity were reduced. The potential applications of CNT-based polymer nanocomposites broaden considerably due to the surface engineering of carbon nanotubes.

Preparation of a thermally conductive biodegradable cellulose nanofiber/hydroxylated boron nitride nanosheet film: the critical role of edge-hydroxylation

Abstract: Chemical modification of boron nitride nanosheets (BNNSs) is a simple but effective method to improve their dispersion and compatibility within polymer nanocomposites. The key point is how to import compatible functional groups but simultaneously retain the intact crystal lattice. In this study, two different hydroxylation methods, namely nitric acid oxidation and aqueous ball milling, were adopted for surface modification of BNNSs. And a comparative study was carried out in terms of hydroxyl (OH) content, position of modification and the thermal conductivity (TC) after mixing them with a biodegradable cellulose nanofiber (CNF). TEM mapping, XRD and HRTEM indicated that nitric acid oxidation mainly resulted in an in-plane hydroxylation of BNNSs (POH-BNNSs) whose crystal lattice was seriously damaged, while aqueous ball milling led to most likely an edge hydroxylation of BNNSs (EOH-BNNSs) whose crystal lattice could be well preserved. As a result, strikingly, the TC of POH-BNNS filled nanocomposites only showed a little growth (10.2%) at a low OH content or even decreased at a higher OH loading, while an impressive thermal enhancement of almost 100% was achieved for CNF/EOH-BNNS nanocomposites. Such a substantial improvement signifies the critical role of edge-hydroxylation, which can simultaneously reduce interfacial thermal resistance and retain the intact basal crystal lattice to facilitate acoustic phonon transfer. This research provides deep insight into modification of two-dimensional nanomaterials from the point of view of the defect position, and an edge-selective modification strategy is expected to be of great advantage for the fabrication of highly thermally conductive nanocomposites.