Effect of nanoparticles on the performance of thermally conductive epoxy adhesives

Microsized or nanosized α‐alumina (Al₂O₃) and boron nitride (BN) were effectively treated by silanes or diisocyanate, and then filled into the epoxy to prepare thermally conductive adhesives. The effects of surface modification and particle size on the performance of thermally conductive epoxy adhesives were investigated. It was revealed that epoxy adhesives filled with nanosized particles performed higher thermal conductivity, electrical insulation, and mechanical strength than those filled with microsized ones. It was also indicated that surface modification of the particles was beneficial for improving thermal conductivity of the epoxy composites, which was due to the decrease of thermal contact resistance of the filler‐matrix through the improvement of the interface between filler and matrix by surface treatment. A synergic effect was found when epoxy adhesives were filled with combination of Al₂O₃ nanoparticles and microsized BN platelets, that is, the thermal conductivity was higher than that of any sole particles filled epoxy composites at a constant loading content. The heat conductive mechanism was proposed that conductive networks easily formed among nano‐Al₂O₃ particles and micro‐BN platelets and the thermal resistance decreased due to the contact between the nano‐Al₂O₃ and BN, which resulted in improving the thermal conductivity. POLYM. ENG. SCI., 50:1809–1819, 2010. © 2010 Society of Plastics Engineers     

Preparation and construction mechanism of thermal conductive epoxy-based composite via magnetic field induced orientation

BN was modified with Fe₃O₄ to confer it with paramagnetic responsivity. The scanning electron microscopy and energy dispersive spectrometer (EDS) results demonstrated that with the assistance of an external magnetic field, the paramagnetic BN particles within an epoxy matrix are effectively aligned along the direction of the magnetic field during the curing process of epoxy resin, hence forming continuous thermal conduction pathways. Therefore, the thermal conductivity of the epoxy-based composite filled with 30 wt% of BN and externally applied with a 50 mT magnetic flux density was 0.7417 (W/m·K), an improvement of 207.89% relative to the pure epoxy resin. The establishment of continuous thermal pathways facilitates effective phonon conduction, thereby further enhancing the thermal conductivity of the material. Meanwhile, this study investigates the chain formation mechanism of Fe₃O₄-modified BN under the influence of a magnetic field. When subjected to an applied magnetic field, the magnetic BN embedded in an epoxy resin matrix undergoes magnetization, rotation, and contact. Subsequently, multiple particles initially form short chains, then aggregate into longer chains aligned with the direction of the magnetic field. The findings indicate that the magnetic field induced particle alignment method holds significant potential in the fabrication of high thermal conductivity polymer composites with low filler loading.     

Solids mixing behavior in a nano-agglomerate fluidized bed

The nano-particles mixing behavior in a nano-agglomerate fluidized bed (NAFB) using R972, a kind of nano-SiO₂ powder, was investigated by the nano-particle coated phosphors tracer method. The axial and radial solids dispersion coefficients in this system were two orders of magnitude lower than those in fluid catalytic cracking (FCC) catalyst systems. The axial solids dispersion coefficient increased with increasing superficial gas velocities, and ranged between 9.1 × 10^− 4 and 2.6 × 10^− 3 m²/s. There was a step increase in the axial solids dispersion coefficient between the particulate fluidization regime and bubbling and turbulent fluidization regimes. As the superficial gas velocity increased, the radial solids dispersion coefficient increased gradually, from 1.2 × 10^− 4 to 4.5 × 10^− 4 m²/s. The much smaller D_a and D_r, compared to regular fluidized systems, is mainly due to the reduced density difference between the fluidized particles and fluidizing medium. To validate this, the solids dispersion coefficients in the NABF were compared with literature values for liquid-solid particulate systems in the particulate fluidization regime and FCC systems in the bubbling and turbulent fluidization regimes. The density difference between the fluidized particles and fluidizing medium and kinetic viscosity of the fluidizing medium, and other hydrodynamic factors like the superficial velocity of the fluidizing medium and the average diameters of the fluidized particles, were the key factors in the solids mixing in the fluidized beds. Empirical correlations are given to describe the results.     

Mechanism of interactions of eggshell microparticles with epoxy resins

Large surface‐area microparticles of natural chicken eggshell were prepared and characterized to illustrate how such particles can improve the toughness of epoxy resins. A small amount of organic compounds, in particular proteins, were found to be present in the microparticles and beneficial to the enhancement of the mechanical properties of the epoxy resins. Scanning electron microscopic analysis of the rough fracture surfaces show that there are full of plastic deformation, voids, cavities, and debonding phenomena in the microparticle‐filled composites. Positron annihilation study indicates that the lifetime of τ₃ o‐Ps varies and the corresponding intensity of I₃ becomes weak with the increase of eggshell particle content, which indicates that there is a good interaction between the epoxy resin and the filling particles. This gives rise to significant improvement in the toughness of the filled resin. The impact strength of the epoxy resin composite reaches 16.7 kJ/m² compared with 9.7 kJ/m² of neat epoxy resin when the epoxy resin composite is filled with only 5 mass% eggshell particles. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Alumina atomic layer deposition nanocoatings on primary diamond particles using a fluidized bed reactor

Ultra-thin alumina films are successfully deposited on primary micron-sized diamond particles in a scalable fluidized bed reactor. The studies of fluidization at reduced pressure show that micron-sized diamond particles can be fluidized with the assistance of vibration. Alumina films are grown at 177 °C by atomic layer deposition (ALD) using sequential exposures of Al(CH₃)₃ and H₂O. The deposited alumina films are characterized by X-ray photoelectron spectroscopy, transmission and scanning electron microscopy, inductively coupled plasma-atomic emission spectroscopy, and surface area. The results indicate that the alumina films are conformally coated on the primary diamond particle surface, and the growth rate of alumina is 0.12 nm per coating cycle.     

Template-directed synthesis of porous alumina particles with precise wall thickness control via atomic layer deposition

Highly porous alumina particles with precise wall thickness control were synthesized by atomic layer deposition (ALD) of alumina on highly porous poly(styrene-divinylbenzene) (PS-DVB) particle templates. Alumina ALD was carried out using alternating reactions of trimethylaluminum and water at 33 °C. The growth rate of alumina was ∼0.3 nm per coating cycle. The wall thickness can be precisely controlled by adjusting the number of ALD coating cycles. Thermo-gravimetric analysis, X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and transmission electron microscopy were used to characterize the fabricated porous alumina particles. The effect of number of ALD coating cycles and calcination temperature on the mesoporous structure of the alumina particles was investigated. γ-Alumina was formed at temperature above 600 °C. Porous alumina particles with a surface area of 80-100 m²/g were obtained and thermally stable at 800 °C. The pore volume of the porous particles can be as high as 1 cm³/g after calcination at 800 °C. Such porous alumina particles may find wide application in nanotechnology and catalysis.     

Effect of atomic layer deposited aluminium oxide on mechanical properties of porous silicon carbide

Silicon carbide nanopowder was coated with amorphous alumina by atomic layer deposition (ALD), using trimethylaluminium Al(CH₃)₃ (TMA) and water as precursors. The ALD experiments were carried out at 300 ^°C, using variable cycle count or changing pulse times at constant cycle count. Depending on deposition conditions, hardness averaging at 14.8 GPa and corresponding reduced elastic modulus of 114 GPa were measured. Maximum hardness values and reduced moduli of elasticity reached 25–30 and 134–202 GPa, respectively, improving the mechanical properties of composites. Increased precursor flow had positive effect on mechanical properties – maximum values of hardness and elastic module reached 35–45 and 218–261 GPa, respectively. In the composites, the mechanical properties were improved compared to pure alumina films or silicon carbide and the brittleness characteristic of SiC particle tablets was decreased.     

Influence of silica nanoparticles added to an organosilane film on carbon steel electrochemical and tribological behaviour

The electrochemical behaviour and tribological properties of carbon steel coated with bis-[trimethoxysilylpropyl]amine (BTSPA) filled with SiO₂ were evaluated. The silane film filled with SiO₂ was prepared by adding different SiO₂ concentrations. The electrochemical behaviour of the coated steel was mainly evaluated by means of open-circuit potential (E_OC), electrochemical impedance spectroscopy (EIS) and polarization curves, in 0.1 mol L⁻¹ NaCl solution. Structural and morphological characterizations were made by optical, electron and atomic force microscopy (AFM). E_OC and EIS data showed that sample filled with 300 ppm SiO₂ presented the highest E_OC and total impedance value. AFM measurements showed a homogeneous particle distribution of SiO₂ particles. Nanohardness measurements showed SiO₂ promoted an increase of the hardness mean value (1.70 ± 0.11 GPa to non-filled BTSPA and 2.21 ± 0.05 GPa for sample filled with 300 ppm SiO₂). Silane films when filled with SiO₂ particles improved the corrosion resistance of the steel substrate. The optimum SiO₂ particles concentration in silane solution is 300 ppm SiO₂. Incorporation of an extra amount of silica into BTSPA film led to degradation of the corrosion protection of the film to the substrate.     

Design and preparation of low-filled magnetic oriented BN@Fe3O4/EP insulating composite with improved thermal conductivity and thermal stability

As an excellent two-dimensional insulating material with high thermal conductivity, high temperature stability and high hardness, hexagonal boron nitride(h-BN) is widely applied in semiconductor manufacturing, aerospace, metallurgical manufacturing and other cutting-edge fields. However, the unique surface structure of h-BN leads to poor lubricity and easy agglomeration, which limits the application of h-BN especially in the field of electronic packaging. To address key issues boosted above, this study designed and prepared the BN@Fe₃O₄ magnetic insulating particles and doped it into the reduced viscosity epoxy resin to prepare the composites. By selecting appropriate external magnetic field strength and BN@Fe₃O₄ particles’ content, a novel 3D structure of fillers like dominoes in epoxy resin composite was successfully constructed. The microstructure of the BN@Fe₃O₄ particles and composites were analyzed, the thermal conductivity, the mechanical and the electrical properties of composites were simultaneously tested. Results manifested that the core-shell structures with BN as core and Fe₃O₄ as shell was successfully prepared, linking through the PDA middle layer between the BN core and Fe₃O₄ shell. Under the influence of magnetic orientation, the BN@Fe₃O₄ magnetic particles were preferred an out-of-plane oriented in the epoxy resin composites, resulted an enormously enhanced on thermal conductivity of composites. At a magnetic field strength of 60 mT and 25 vol% BN@Fe₃O₄ content, the thermal conductivity of BN@Fe₃O₄/EP composites is as lofty as 1.832 W/(m K), which is 1023.46% higher than that of pure epoxy resin. Meanwhile, the thermal stability has also been slightly improved, the elastic modulus and insulation performances remain at the same level.     

MXene fillers and silver flakes filled epoxy resin for new hybrid conductive adhesives

The addition of V₂CT_x two-dimensional materials as auxiliary fillers in conductive adhesives can increase the contact area between conductive particles inside the matrix effectively reducing the resistivity of epoxy resin conductive adhesives. The V₂CT_x/Ag/rGO/MWCNTs fillers inside the epoxy resin will connect more Ag-clad Cu particles to form a conductive pathway, but its excessive content will be aggregated inside and thus increase the resistivity of the conductive adhesive. The volume resistivity of ECAs increases from 4.4 × 10⁻⁶ Ω m to 1.15 × 10⁻⁵ Ω m when the V₂CT_x/Ag/rGO/MWCNTs content of 0.1% increases to 0.34%. The Ag-clad Cu particles are interconnected inside the epoxy resin to form an electron transfer network. Inside the epoxy resin substrate Ag-clad Cu particles and V₂CT_x/Ag/rGO/MWCNTs interconnects to form a larger conductive network, so that the conductive adhesive shows good conductive properties.     

Scratch resistance and oxygen barrier properties of acrylate-based hybrid coatings on polycarbonate substrate

Organic/inorganic hybrid coating materials were synthesized using acrylate end-capped polyester, 1,6-hexanediolacrylate, tetraethoxysilane (TEOS), and 3-trimethoxysilylpropylmethacrylate (TMSPM). The hybrid materials were cast onto a polycarbonate (PC) substrate and cured by UV irradiation to give a hybrid film with covalent linkage between the inorganic and the organic networks. The coating layer was characterized by FT-IR and ²⁹Si-NMR, and pencil hardness and oxygen permeation rate of coated films were investigated. The pencil hardness of all samples examined in this study was higher than 1H, whereas that of uncoated PC substrate was 6B. The hardness enhancement after coating may due to incorporation of organic acrylate resin. The oxygen permeability coefficient of the film coated with hybrid material on 3-aminopropyltriethoxysilane (APTEOS) pretreated polycarbonate substrate was 1.67×10⁻³ GPU, the lowest value in this work, whereas that of uncoated PC substrate was 8.07×10⁻³ GPU. The lower oxygen permeation rates of these films are attributed to the good adhesion between organic/inorganic hybrid coating layer and PC substrate and a dense structure induced by an increase of network density.     

Crack propagation and residual stress in laminated Si3N4/BN composite structures

The level of residual stress and crack propagation in a new generation of laminates, based on silicon nitride (Si₃N₄) layer and a mixture of boron nitride (BN) and alumina (Al₂O₃) interlayer, was presented. The structure consists of alternated concentric rings of Si₃N₄ separated by the weak BN interlayer possessing no planes of easy crack propagation and fracture resistance much larger than that of any classical planar laminates. The results on direction of crack propagation and residual stress in relation to inter-layer composition, the number of layers, and their thickness are investigated and reported. The effect of residual stress on crack propagation was studied by using Vicksrs intentation. The highest compressive residual stress of ∼170 MPa was found in samples with five layers possessing an average layer thickness of ∼310 × 10⁻⁶ m.     

Ultralow Tribological Properties of Polymer Composites Containing [BMIm]PF6‐Loaded Multilayer Wall Microcapsule

Multilayer wall microcapsules efficiently loaded with a lubricant (ionic liquid [BMIm]PF₆) are successfully synthesized via a combination of interfacial and in situ polymerization reactions based on lignin nanoparticle–stabilized Pickering emulsion templates. The resulting microcapsules are spherical in shape, with an ideal structure of a rough outer surface and a smooth inner surface. The mean diameter and wall thickness of the resultant microcapsules are 52 ± 18 µm and 3–6 µm. The core fraction is ≈71.29 wt%. Compared with the pure epoxy resin, the friction coefficient of self‐lubricating composites decreases by 83.6% (from 0.55 to 0.09) and the wear rate decreases by 218 times (from 76.8 × 10^?14 to 0.352 × 10^?14 m³ N^?1 m^?1) by incorporating 20 wt% of the resultant microcapsules into the epoxy resin. It is demonstrated that [BMIm]PF₆, a more efficient lubricant, release from the microcapsules during the friction process produced a boundary lubricating film. The bipolar property of [BMIm]PF₆ makes the lubricating film firmer, which can efficiently prevent direct contact between the resin matrix and counterface. Furthermore, the rough poly(urea‐formaldehyde) outer surface of multilayer microcapsules brings in an improved interface property between the microcapsules and resin matrix.     

The effect of a carbon layer on the microstructural and mechanical properties of porous BN/Si3N4 ceramic brazed with a titanium-silicon filler

The Ti₂₂Si₇₈ (wt.%) braze was used to bond porous BN/Si₃N₄ ceramic. The results revealed that the joint strength was low. In order to improve the joint strength, a carbon coated modification of the porous BN/Si₃N₄ substrate, achieved by the pyrolysis of phenol-formaldehyde resin was suggested. The thickness of carbon layer was controlled by the volume ratio of phenol-formaldehyde resin and methyl alcohol (R/M). The effect of the carbon layer on the microstructure and mechanical properties of the joint was examined. It was established that the maximum joint strength was achieved at the level of 80 MPa (as opposed to the uncoated joint with only 30 MPa) when R/M was 1:2, at the given brazing temperature. The improvement of the joint strength is attributed mainly to the formation of a SiC infiltration reaction layer, a significant population of SiC nanowires, as well as TiN_0.7C_0.3 and TiB₂ particles.     

Effective surface treatments for enhancing the thermal conductivity of BN‐filled epoxy composite

To improve the thermal conductivity of BN‐filled epoxy composite, admicellar polymerization was used to coat polystyrene and polymethyl methacrylate on the BN surface to improve the interfacial adhesion in the composite. The treated surface was characterized by FTIR and contact angle measurements. The results show that the admicellar treatment led to improved wettability of epoxy resin on the treated surface. Thermal conductivity of the composite increased from 1.5 W/mK for untreated BN to 2.69 W/mK when the admicellar‐treated BN was used, indicating improvement in the interfacial adhesion between BN and epoxy resin in the composite. The mechanical properties of the composite also improved significantly. The surfactant : monomer molar ratio of 1 : 10 was found to be the optimum condition for the admicellar polymerization process. The solubility parameter concept was used to explain the difference in the effectiveness of polystyrene and polymethyl methacrylate. When compared to the more conventional silane treatment, admicellar treatment was found to be more effective in improving the interfacial adhesion between the BN particles and epoxy resin. SEM micrographs of the fractured surface of the composite further confirm the improvement in the interfacial adhesion after the admicellar treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cold plasma modification of boron nitride fillers and its effect on the thermal conductivity of silicone rubber/boron nitride composites

Hexagonal boron nitride (h‐BN) fillers were first coated with low‐molecular‐weight polydimethylsiloxane (PDMS) by solution dispersion and then treated in argon plasma for different times. The modified h‐BN fillers were characterized by high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and contact angle analysis. The results revealed that a thin PDMS film several nanometers thick was tightly coated on the surface of the h‐BN filler after plasma treatment, and this thin film could not be removed by 48 h Soxhlet extraction with n‐hexane at 120°C. Furthermore, the effect of plasma modification on the h‐BN filled silicone rubber composites was investigated. The results indicated that the plasma modification improved the interfacial interaction between h‐BN and the matrix, but hardly affected the distribution state of the h‐BN in the composites. The composites filled with the modified h‐BN exhibit significantly higher thermal conductivity than the composites filled with untreated h‐BN. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effect of BN or B4C content on physical and tribological properties of copper-clad laminates reinforced with carbon fiber and epoxy resin

Plasma treatment was used to improve the surface roughness of copper foil. The copper-clad laminates reinforced with carbon fiber, boron nitride (BN), or boron carbide (B₄C), and epoxy resin were prepared by hot pressing. The effect of BN or B₄C content on the physical properties and tribological properties of copper-clad laminates reinforced with carbon fiber and epoxy resin were studied. The resulting copper-clad laminate exhibited desirable properties, such as dielectric constant, peel strength, oxygen index, and arc resistance, which were influenced by the concentration of BN or B₄C particles. Additionally, the wear and friction properties of the laminate were evaluated, revealing the effects of load, sliding speed, and particle content on weight loss, specific wear rate, and coefficient of friction. SEM analysis of worn surfaces provided insight into the stages of wear, highlighting the importance of an oxide layer in reducing wear and protecting the copper surface.     

Anticorrosive properties of epoxy resin coatings cured by aniline/p‐phenylenediamine copolymer

Aniline/p‐phenylenediamine copolymer [poly(ANI‐co‐p‐PDA)] was prepared by chemical oxidative polymerization. FTIR and ¹H‐NMR analysis indicate that the poly(ANI‐co‐p‐PDA) is oligomer with end‐capped amino groups, which can cure epoxy resin. The anticorrosion performance of carbon steel (CS) samples coated by epoxy resin coating cured with poly(ANI‐co‐p‐PDA) and epoxy resin coating cured with triethylenetetramine exposed to 5 wt % NaCl and 0.1 mol/L HCl aqueous solution is studied by the potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the CS coated by epoxy resin coating cured with poly (ANI‐co‐p‐PDA) has more excellent corrosion protection than that of epoxy resin coating cured with triethylenetetramine. Raman spectroscopy analysis indicates that the surface of CS coated by epoxy resin coating cured with poly(ANI‐co‐p‐PDA) forms passive layer, which is composed of α‐Fe₂O₃. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and properties of SiCnw-reinforced SiC composites by reactive melt infiltration with BN and PyC interface

To tailor the fiber–matrix interface of SiC nanowires-reinforced SiC (SiC_nw/SiC) ceramic matrix composites (CMCs) for improved mechanical properties, SiC nanowires were coated with BN and pyrolytic carbon (PyC) compound coatings prepared by the dip-coating process in boric acid and urea solution and the pyrolysis of phenolic resin. SiC_nw/SiC CMC with PyC/BN interfaces were fabricated by reactive melt infiltration (RMI) at 1680°C for 1 h. The influences of phenolic resin content on the microstructure and mechanical properties of the CMC were investigated. The results showed that the flexural strength and fracture toughness reach the maximum values of 294 MPa and 4.74 MPa m^1/2 as the phenolic resin content was 16 and 12 wt%, respectively. The displacement–load curve of the sample exhibited a gradient drop with increasing phenolic resin content up to 12 wt%. The results demonstrated that the PyC/BN compound coatings could play the role of protecting the SiC_nw from degradation as well as improving the more moderate interfacial bonding strengths during the RMI.     

Coating organic pigment particles with hydrous alumina through direct precipitation

A novel coating process of hydrous alumina on organic pigment particles through direct precipitation in aqueous solution was developed in this work. The aqueous suspensions of organic pigment particles were prepared using cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS) as additives before the coating. The organic pigment particles were then coated with hydrous alumina using Al₂(SO₄)₃ as precursor. The morphology and surface states of as-coated organic pigment particles were analyzed by high-resolution transmission electron microscopy (HRTEM) and zeta-potential. TEM images showed that a uniform hydrous alumina film could be formed on the organic pigment particle surface with anion surfactant SDBS. However, with cation surfactant CTAB, no alumina coating film was generated on the organic pigment particle surface.