Interfacial modification of boron nitride nanoplatelets for epoxy composites with improved thermal properties

Enhancement of Fracture Toughness of Epoxy Nanocomposites by Combining Nanotubes and Nanosheets as Fillers

In this work the fracture toughness of epoxy resin has been improved through the addition of low loading of single part and hybrid nanofiller materials. Functionalised multi-walled carbon nanotubes (f-MWCNTs) was used as single filler, increased the critical strain energy release rate, G_IC, by 57% compared to the neat epoxy, at only 0.1 wt% filler content. Importantly, no degradation in the tensile or thermal properties of the nanocomposite was observed compared to the neat epoxy. When two-dimensional boron nitride nanosheets (BNNS) were added along with the one-dimensional f-MWCNTs, the fracture toughness increased further to 71.6% higher than that of the neat epoxy. Interestingly, when functionalised graphene nanoplatelets (f-GNPs) and boron nitride nanotubes (BNNTs) were used as hybrid filler, the fracture toughness of neat epoxy is improved by 91.9%. In neither of these hybrid filler systems the tensile properties were degraded, but the thermal properties of the nanocomposites containing boron nitride materials deteriorated slightly.

Computational Thermomechanical Properties of Silica⁻Epoxy Nanocomposites by Molecular Dynamic Simulation

Silica⁻epoxy nanocomposite models were established to investigate the influence of silane coupling agent on the structure and thermomechanical properties of the nanocomposites through molecular dynamics simulation. Results revealed that incorporating silica nanoparticles into a polymer matrix could improve thermomechanical properties of the composites and increase their glass transition temperature and thermal conductivity. Their thermomechanical properties were further enhanced through silane coupling agent modification on the surface of fillers. Compared with that of pure epoxy, the glass transition temperatures of the silica⁻epoxy composites with grafting ratios of 5% and 10% increased by 17 and 28 K, respectively. The thermal conductivities of the two models at room temperature respectively increased by 60.0% and 67.1%. At higher temperature 450 K, thermal conductivity of the nanocomposite model with a high grafting ratio of 10% demonstrated a considerable increase of approximately 50% over the pure epoxy resin (EP) model. The elastic and shear modulus of the nanocomposite models decreased at temperatures below their glass transition temperatures. These observations were further addressed in the interpretation from three aspects: segmental mobility capability, radial distribution function, and free volume fraction. Our computational results are largely consistent with existing experimental data, and our simulation model got fully validated.

Effect of Interfacial Polarization and Water Absorption on the Dielectric Properties of Epoxy-Nanocomposites

Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm-1. In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm-1; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm-1. In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study.

Geometric and electronic structures of monolayer hexagonal boron nitride with multi-vacancy

Hexagonal boron nitride (h-BN) is an electrical insulator with a large band gap of 5 eV and a good thermal conductor of which melting point reaches about 3000 °C. Due to these properties, much attention was given to the thermal stability rather than the electrical properties of h-BN experimentally and theoretically. In this study, we report calculations that the electronic structure of monolayer h-BN can be influenced by the presence of a vacancy defect which leads to a geometric deformation in the hexagonal lattice structure. The vacancy was varied from mono- to tri-vacancy in a supercell, and different defective structures under the same vacancy density were considered in the case of an odd number of vacancies. Consequently, all cases of vacancy defects resulted in a geometric distortion in monolayer h-BN, and new energy states were created between valence and conduction band with the Fermi level shift. Notably, B atoms around vacancies attracted one another while repulsion happened between N atoms around vacancies, irrespective of vacancy density. The calculation of formation energy revealed that multi-vacancy including more B-vacancies has much lower formation energy than vacancies with more N-vacancies. This work suggests that multi-vacancy created in monolayer h-BN will have more B-vacancies and that the presence of multi-vacancy can make monolayer h-BN electrically conductive by the new energy states and the Fermi level shift.

Polymer Composite with Improved Thermal Conductivity by Constructing a Hierarchically Ordered Three-Dimensional Interconnected Network of BN

In this work, we report a fabrication of epoxy resin/ordered three-dimensional boron nitride (3D-BN) network composites through combination of ice-templating self-assembly and infiltration methods. The polymer composites possess much higher thermal conductivity up to 4.42 W m^-1 K^-1 at relatively low loading 34 vol % than that of random distribution composites (1.81 W m^-1 K^-1 for epoxy/random 3D-BN composites, 1.16 W m^-1 K^-1 for epoxy/random BN composites) and exhibit a high glass transition temperature (178.9-229.2 °C) and dimensional stability (22.7 ppm/K). We attribute the increased thermal conductivity to the unique oriented 3D-BN thermally conducive network, in which the much higher thermal conductivity along the in-plane direction of BN microplatelets is most useful. This study paves the way for thermally conductive polymer composites used as thermal interface materials for next-generation electronic packaging and 3D integration circuits.

Boron nitride nanotubes and nanoplatelets as reinforcing agents of polymeric matrices for bone tissue engineering

This study investigates the mechanical properties and in vitro cytotoxicity of one- and two-dimensional boron nitride nanomaterials-reinforced biodegradable polymeric nanocomposites. Poly(propylene fumarate) (PPF) nanocomposites were fabricated using crosslinking agent N-vinyl pyrrolidone and inorganic nanomaterials: boron nitride nanotubes (BNNTs) and boron nitride nanoplatelets (BNNPs) dispersed at 0.2 wt % in the polymeric matrix. The incorporation of BNNPs and BNNTs resulted in a ∼38 and ∼15% increase in compressive (Young's) modulus, and ∼31 and ∼6% increase in compressive yield strength compared to PPF control, respectively. The nanocomposites showed a time-dependent increased protein adsorption for collagen I protein. The cytotoxicity evaluation of aqueous BNNT and BNNP dispersions (at 1-100 μg/mL concentrations) using murine MC3T3 preosteoblast cells showed ∼73-99% viability. The cytotoxicity evaluation of media extracts of nanocomposites before crosslinking, after crosslinking, and upon degradation (using 1×-100× dilutions) showed dose-dependent cytotoxicity responses. Crosslinked nanocomposites showed excellent (∼79-100%) cell viability, cellular attachment (∼57-67%), and spreading similar to cells grown on the surface of tissue culture polystyrene control. The media extracts of degradation products showed a dose-dependent cytotoxicity. The favorable cytocompatibility results in combination with improved mechanical properties of BNNT and BNNP nanocomposites opens new avenues for further in vitro and in vivo safety and efficacy studies towards bone tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 406-419, 2017.

Thermal Conductivity Performance of Polypropylene Composites Filled with Polydopamine-Functionalized Hexagonal Boron Nitride

Mussel-inspired approach was attempted to non-covalently functionalize the surfaces of boron nitride (BN) with self-polymerized dopamine coatings in order to reduce the interfacial thermal barrier and enhance the thermal conductivity of BN-containing composites. Compared to the polypropylene (PP) composites filled with pristine BN at the same filler content, thermal conductivity was much higher for those filled with both functionalized BN (f-BN) and maleic anhydride grafted PP (PP-g-ma) due to the improved filler dispersion and better interfacial filler-matrix compatibility, which facilitated the development of more thermal paths. Theoretical models were also applied to predict the composite thermal conductivity in which the Nielsen model was found to fit well with the experimental results, and the estimated effective aspect ratio of fillers well corresponded to the degree of filler aggregation as observed in the morphological study.

Non-covalent functionalized hexagonal boron nitride nanoplatelets to improve corrosion and wear resistance of epoxy coatings

In the present study, a non-covalent method was employed to modify hexagonal boron nitride (h-BN) nanoplateletsviaπ–π interaction of amine-capped aniline trimer (AT), which resulted in a stable dispersion of h-BN nanoplatelets in organic solvents.

Flame retarding epoxy composites with poly(phosphazene-co-bisphenol A)-coated boron nitride to improve thermal conductivity and thermal stability

A novel poly(cyclotriphosphazene-co-bisphenol A)-coated boron nitride (PCB-BN) was synthesized by in situ polymerization on the surface of BN. The epoxy/PCB-BN composites showed the enhanced thermal conductivity with the improved flame retardance.

Surface modification and magnetic alignment of hexagonal boron nitride nanosheets for highly thermally conductive composites

The highly ordered thermoplastic polyurethane elastomer (TPU)/BNNSs composites are successfully prepared by the combination of filler modification and magnetic alignment.

Thermally conductive, dielectric PCM-boron nitride nanosheet composites for efficient electronic system thermal management

Phase change materials (PCMs) possessing ideal properties, such as superior mass specific heat of fusion, low cost, light weight, excellent thermal stability as well as isothermal phase change behavior, have drawn considerable attention for thermal management systems. Currently, the low thermal conductivity of PCMs (usually less than 1 W mK^-1) greatly limits their heat dissipation performance in thermal management applications. Hexagonal boron nitride (h-BN) is a two-dimensional material known for its excellent thermally conductive and electrically insulating properties, which make it a promising candidate to be used in electronic systems for thermal management. In this work, a composite, consisting of h-BN nanosheets (BNNSs) and commercialized paraffin wax was developed, which inherits high thermally conductive and electrically insulating properties from BNNSs and substantial heat of fusion from paraffin wax. With the help of BNNSs, the thermal conductivity of wax-BNNS composites reaches 3.47 W mK^-1, which exhibits a 12-time enhancement compared to that of pristine wax (0.29 W mK^-1). Moreover, an 11.3-13.3 MV m^-1 breakdown voltage of wax-BNNS composites was achieved, which shows further improved electrical insulating properties. Simultaneously enhanced thermally conductive and electrically insulating properties of wax-BNNS composites demonstrate their promising application for thermal management in electronic systems.

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

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, giving few-layered NF-BNNSs in high yields (up to ∼25%). The crystallinity of the NF-BNNS was perfectly maintained even after CSA treatment. The physical adsorption of CSAs imparted high solubility for BNNSs in various organic solvents, yielding NF-BNNS uniformly dispersed-thermoplastic polymer composite films through a simple wet-process using predispersed NF-BNNS solutions. Random dispersion of NF-BNNSs in thermoplastic polymer films dramatically enhanced both the in- and through-plane thermal conductivities (>10 W m^-1 K^-1). The through-plane thermal conductivity of the NF-BNNS/polybutylene terephthalate (PBT) composite films was much greater (up to 11.0 W m^-1 K^-1) than those previously reported for BNNS/thermoplastic polymer composites (≤2.6 W m^-1 K^-1). These results are also due to an increase of interactions between the BNNS and polymer matrices, caused by physical adsorption of CSAs on BNNS surfaces. Moreover, the volume resistivity of the NF-BNNS/PBT composite films was significantly improved compared with pristine PBT. The NF-BNNS/polymer composites are very promising as highly thermally conductive and electrically insulating materials in various applications.

Improved thermal conductivity of epoxy composites prepared with a mixed filler of multiwalled carbon nanotubes and aluminum nitride particles

The thermal conductive filler/epoxy resin (EP) composites were prepared by a casting method. The effects of the multiwalled carbon nanotubes (MWCNTs), aluminum nitride (AlN) particles, and their compounds on the microstructure and thermal conductivity of the composites were investigated, in addition to the thermal properties. The results indicated that compounds of MWCNTs and AlN particles exhibited a remarkable synergistic effect to improve the thermal conductivity properties of the composites. The one-dimensional MWCNTs with superb thermal conductivity bridged the AlN particles to form an excellent network, which provides a faster and more effective pathway for phonon transport in the composites. The thermal conductivity of the 0.6 vol% MWCNTs/3.4 vol% AlN/EP composite is 0.53 W (m K)−1. In addition, the thermal conductivity of the MWCNTs/AlN/EP composites with 0.4 vol% MWCNTs and 3.4 vol% AlN is 0.48 W (m K)−1 (which is twice the value of 0.24 W (m K)−1 for the pure EP) which was much higher than the 0.4 vol% MWCNTs/EP composites (0.27 W (m K)−1) and the 3.4 vol% AlN/EP composites (0.28 W (m K)−1). Bruggeman’s equation is identified to fit quite well to the experimental results of the AlN/EP composites in the entire range of volume percentage of AlN; however, the MWCNTs/EP composites coincided better to the Russell equation. The volume resistivity of the MWCNTs/AlN/EP composites (approximately 1.8–2.6 × 1012 Ω m) exhibited only a slight compromise in comparison to the pure EP (2.5 × 1014 Ω m), which manifested the excellent insulation characteristic of these composites.

Fabrication of Boron Nitride Nanosheets by Exfoliation

Nanomaterials with layered structures, with their intriguing properties, are of great research interest nowadays. As one of the primary two-dimensional nanomaterials, the hexagonal boron nitride nanosheet (BNNS, also called white graphene), which is an analogue of graphene, possesses various attractive properties, such as high intrinsic thermal conductivity, excellent chemical and thermal stability, and electrical insulation properties. After being discovered, it has been one of the most intensively studied two-dimensional non-carbon nanomaterials and has been applied in a wide range of applications. To support the exploration of applications of BNNSs, exfoliation, as one of the most promising approaches to realize large-scale production of BNNSs, has been intensively investigated. In this review, methods to yield BNNSs by exfoliation will be summarized and compared with other potential fabrication methods of BNNSs. In addition, the future prospects of the exfoliation of h-BN will also be discussed.

Dielectric Properties and Energy Storage Densities of Poly(vinylidenefluoride) Nanocomposite with Surface Hydroxylated Cube Shaped Ba0.6Sr0.4TiO₃ Nanoparticles

Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba0.6Sr0.4TiO₃ nanoparticles (BST⁻NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants of the nanocomposite with surface hydroxylated BST⁻NPs (BST⁻NPs⁻OH) were higher as compared with those of their untreated BST⁻NPs composites. The sample with 40 vol % BST⁻NPs⁻OH had a dielectric constant of 36 (1 kHz). Different theoretical models have been employed to predict the dielectric constants of the nanocomposites, in order to compare with the experimental data. The BST⁻NPs⁻OH/PVDF composites also exhibited higher breakdown strength than their BST⁻NP/PVDF counterparts. A maximal energy density of 3.9 J/cm³ was achieved in the composite with 5 vol % BST⁻NPs⁻OH. This hydroxylation strategy could be used as a reference to develop ceramic-polymer composite materials with enhanced dielectric properties and energy storage densities.

Fabrication of oriented hBN scaffolds for thermal interface materials

Three dimensional scaffolds of hBN microplatelets prepared by ice templating method are used to fabricate hBN/PDMS composites with vertically aligned hBN for thermal interface materials.

Double glass transitions in exfoliated poly(methyl methacrylate)/organically modified MgAl layered double hydroxide nanocomposites

PMMA chains were confined at a layered material (organically modified MgAl layered double hydroxides) surface, which formed the interfacial layer between nanoparticles and the polymer matrix.

Preparation and properties of thermally conductive polyimide/boron nitride composites

Hexagonal boron nitride micro particles functionalized by γ-MPS, were used to fabricate PI/BN composites. The thermal conductivity of the composites with 40 wt% m-BN content was increased to 0.748 W m⁻¹ K⁻¹, 4.5 times higher than that of the pure PI.

Effects of 2-D transition metal carbide Ti2CTxon properties of epoxy composites

By means ofin situintercalation polymerization Ti₂CT_x/EP nanocomposites were prepared, which possessed excellent mechanical and tribological properties.

Boron nitride@graphene oxide hybrids for epoxy composites with enhanced thermal conductivity

Boron nitride/graphene oxide hybrids prepared by an electrostatic self-assembly strategy were used as fillers for epoxy composites with high thermal conductivity.

Fabrication of h-BN nano-sheet composite and evaluation of microcosmic physical interfaces effect on thermal diffusion

Microcosmic physical interfaces are experimentally proven to be playing the decisive role in thermal diffusion of polymeric composite.

Fabrication of highly oriented hexagonal boron nitride nanosheet/elastomer nanocomposites with high thermal conductivity

A homogeneous dispersion of hexagonal boron nitride nanosheets (BNNSs) in elastomers is obtained by solution compounding methods, and a high orientation of BNNSs is achieved by strong shearing. The composites show high thermal conductivities, especially when BNNS loading exceeds 17.5 vol%, indicating that the material is promising for thermal-management applications which need high thermal conductivity, low dielectric constant, and adequate softness.

Bioinspired modification of h-BN for high thermal conductive composite films with aligned structure

With the development of microelectronic technology, the demand of insulating electronic encapsulation materials with high thermal conductivity is ever growing and much attractive. Surface modification of chemical inert h-BN is yet a distressing issue which hinders its applications in thermal conductive composites. Here, dopamine chemistry has been used to achieve the facile surface modification of h-BN microplatelets by forming a polydopamine (PDA) shell on its surface. The successful and effective preparation of h-BN@PDA microplatelets has been confirmed by SEM, EDS, TEM, Raman spectroscopy, and TGA investigations. The PDA coating increases the dispersibility of the filler and enhances its interaction with PVA matrix as well. Based on the combination of surface modification and doctor blading, composite films with aligned h-BN@PDA are fabricated. The oriented fillers result in much higher in-plane thermal conductivities than the films with disordered structures produced by casting or using the pristine h-BN. The thermal conductivity is as high as 5.4 W m(-1) K(-1) at 10 vol % h-BN@PDA loading. The procedure is eco-friendly, easy handling, and suitable for the practical application in large scale.

Multifunctional cyanate ester nanocomposites reinforced by hexagonal boron nitride after noncovalent biomimetic functionalization

Boron nitride (BN) reinforced polymer nanocomposites have attracted a growing research interest in the microelectronic industry for their uniquely thermal conductive but electrical insulating properties. To overcome the challenges in surface functionalization, in this study, hexagonal boron nitride (h-BN) nanoparticles were noncovalently modified with polydopamine in a solvent-free aqueous condition. The strong π-π interaction between the hexagonal structural BN and aromatic dopamine molecules facilitated 15 wt % polydopamine encapsulating the nanoparticles. High-performance bisphenol E cyanate ester (BECy) was incorporated by homogeneously dispersed h-BN at different loadings and functionalities to investigate their effects on thermo-mechanical, dynamic-mechanical, and dielectric properties, as well as thermal conductivity. Different theoretical and empirical models were successfully applied to predict thermal and dielectric properties of h-BN/BECy nanocomposites. Overall, the prepared h-BN/BECy nanocomposites exhibited outstanding performance in dimensional stability, dynamic-mechanical properties, and thermal conductivity, together with the controllable dielectric property and preserved thermal stability for high-temperature applications.

Thermally conductive, electrically insulating and melt-processable polystyrene/boron nitride nanocomposites prepared by in situ reversible addition fragmentation chain transfer polymerization

Thermally conductive and electrically insulating polymer/boron nitride (BN) nanocomposites are highly attractive for various applications in many thermal management fields. However, so far most of the preparation methods for polymer/BN nanocomposites have usually caused difficulties in the material post processing. Here, an in situ grafting approach is designed to fabricate thermally conductive, electrically insulating and post-melt processable polystyrene (PS)/BN nanosphere (BNNS) nanocomposites by initiating styrene (St) on the surface functionalized BNNSs via reversible addition fragmentation chain transfer polymerization. The nanocomposites exhibit significantly enhanced thermal conductivity. For example, at a St/BN feeding ratio of 5:1, an enhancement ratio of 1375% is achieved in comparison with pure PS. Moreover, the dielectric properties of the nanocomposites show a desirable weak dependence on frequency, and the dielectric loss tangent of the nanocomposites remains at a very low level. More importantly, the nanocomposites can be subjected to multiple melt processing to form different shapes. Our method can become a universal approach to prepare thermally conductive, electrically insulating and melt-processable polymer nanocomposites with diverse monomers and nanofillers.

Preparation of alumina-coated graphite for thermally conductive and electrically insulating epoxy composites

Volume resistivity of epoxy composites containing various fillers and amounts of filler particles.

Liquid phase exfoliation and crumpling of inorganic nanosheets

Experiment and simulation demonstrate the polymer-assisted dispersion of inorganic 2D layered nanomaterials such as boron nitride nanosheets (BNNSs), MoS₂ nanosheets, and WS₂ nanosheets; spray drying can be used to alter such nanosheets into a crumpled morphology.

Effects of h-BN on the thermal and mechanical properties of PBT/PC/ABS blend based composites

H-BNMPs were shown to have an obvious effect on the thermal conductivity of the blend. The addition of h-BN hybrids enhanced the mechanical properties of composites with remarkably improvement of the thermal conductivity.

Enhanced thermal properties in a hybrid graphene–alumina filler for epoxy composites

The inclusion of hybrid LCPBI/RGO and Al₂O₃-APS fillers into a polymer matrix with formation of composites has proven to be an efficient way to improve thermal properties of the composites.