End group effect on surface and interfacial segregation in PS-PMMA blend thin films

Thin films of polystyrene (PS)/poly (methyl methacrylate) (PMMA) blends with different end groups were investigated using ToF-SIMS and AFM. PS with -OH and -NH₂ end groups were blended in toluene solvent with pure PMMA homopolymer, and PMMA having anhydride end group. The ToF-SIMS spectra of PS-OH/PMMA resembled that of pure PS-PMMA blends showing an increase of PMMA intensity after annealing. On the contrary, the PS-NH₂ blended with PMMA showed an increase in PS intensity on the surface after annealing. The ToF-SIMS spectra were similar to that of a pure PS-PMMA di-block copolymer. These results indicate copolymer formation at the surface. The PS-NH₂ with PMMA-anhydride blend spectra showed very slight changes in spectra before and after annealing and the AFM images revealed spinodal bi-continuous structures on the surface before and after annealing. The copolymer formation is found to occur in the as-cast film itself and not after thermal treatment.     

PVDF/PS/HDPE/MWCNTs/Fe3O4 nanocomposites: Effective and lightweight electromagnetic interference shielding material through the synergetic effect of MWCNTs and Fe3O4 nanoparticles

In this work, Polyvinylidene Fluoride (PVDF)/polystyrene (PS)/high density polyethylene (HDPE) ternary blends displayed a core-shell structure where HDPE was the core, PS was the shell, and this core-shell system dispersed in PVDF matrix. Here, multiwall carbon nanotubes (MWCNTs) and ferroferric oxide (Fe₃O₄) was incorporated. F-F composites with MWCNTs was in PS shell and Fe₃O₄ was in PVDF matrix and E-F composites with MWCNTs was in PS shell and Fe₃O₄ was in HDPE core were fabricated by melt blending. It was indicated that the core-shell morphology between PS and HDPE was well retained with the incorporation of Fe₃O₄ and MWCNTs. Both the electrical conductivity of F-F and E-F composites were similar without no obvious change with the incorporation of Fe₃O₄. Composites with greater than 20 dB shielding effectiveness were easy to obtain. The highest SE we observed was for the F-F composite with 1 vol% Fe₃O₄ and 1 vol% MWCNTs was 25 dB at 9.5 GHz, and the SE was over 20 dB in the whole measured frequency(X-band). The E-F composites with SE greater than 20 dB in X-band was at 2 vol% Fe₃O₄ and 1 vol% MWNCTs. Such effective and lightweight nanocomposites were obtained, resulting from the synergetic effect of MWCNTs and Fe₃O₄ nanoparticles.     

Preparation and characterization of low density polystyrene/TiO2 core–shell particles for electronic paper application

In order to reduce the density mismatch between TiO₂ and the low dielectric medium and improve the dispersion stability of the electrophoretic particles in the low dielectric medium for electrophoretic display application, polystyrene/titanium dioxide (PS/TiO₂) core–shell particles were prepared via in-situ sol–gel method by depositing TiO₂ on the PS particle which was positively charged with 2-(methacryloyloxy)ehyl trimethylammonium chloride (DMC). The morphology and average particle size of PS/TiO₂ core–shell particles were observed by transmission electron microscopy (TEM), scanning electron microscope (SEM) and particle size analyzer. It was found that density of PS/TiO₂ core–shell particles were reduced obviously and the particles can suspend in the low dielectric medium of low density. The PS/TiO₂ core–shell particles can endure ultrasonic treatment because of the interaction between TiO₂ and PS. Zeta potential and electrophoretic mobility of the fabricated core–shell particles in a low dielectric medium with charge control agent was measured to be −44.3 mV and −6.07 × 10⁻⁶ cm²/Vs, respectively, which presents potential in electronic paper application.     

Electrospun polystyrene fibres on TiO<Subscript>2</Subscript> nanostructured film to enhance the hydrophobicity and corrosion resistance of stainless steel substrates

A dual layer of dip-coated TiO₂ film (top layer) and electrospun polystyrene (bottom layer) was coated on stainless steel (SS) substrates. The morphological and structural studies were performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their hydrophobicity and corrosion resistance were also investigated using contact angle (CA) and electrochemical corrosion tests in acidic and salt solutions, respectively. Contact angle results showed that the naturally hydrophilic TiO₂/SS sample (CA ～ 66^°) turned into a superhydrophic surface (CA ～ 148^°) when it was covered by polystyrene fibres (PS /TiO₂ /SS). This observation can be attributed to the intrinsic hydrophobicity of organic polystyrene fibres (due to their low surface energy) and also to the existence of trapped air bubbles between fibres. Electrochemical corrosion tests showed that the corrosion rate was substantially decreased by using a protective bilayer (PS /TiO₂) from 33 to 0.39 mV /y for bare SS sample and from 0.01 to 0.003 mV /y for PS /TiO₂ /SS sample in 1 M salt and acidic solutions, respectively. The superhydrophobic protective layer forms an obstacle against ionic exchange interactions. Therefore, it slows down the breaking of the surface oxidic layer on the metal substrate and prevents the metallic surface underneath from further corrosion.     

Preparation and Characterization of Nano‐TiO2 Doped Polystyrene Materials by Melt Blending for Inertial Confinement Fusion

Abstract

Nano‐TiO₂ doped polystyrene (PS) materials (TiO₂‐d‐PS) used for inertial confinement fusion (ICF) targets were prepared by means of melt blending. The effect of the pretreatment process, including coupling agents and ultrasonic dispersion on nano‐TiO₂, was studied. Tensile tests were conducted to evaluate the mechanical properties of the TiO₂‐d‐PS materials. Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to characterize the degree of dispersion of nano‐TiO₂ in the PS matrix. Transmission electron microscopy (TEM) and dynamic contact angle (DCA) measurements were introduced to demonstrate the surface state of untreated and pretreated nano‐TiO₂. The results showed that coupling agents improved the interfacial adhesion between the PS matrix and dopants; ultrasonic dispersion contributed to the increase in the tensile properties of the TiO₂‐d‐PS materials. The dispersion stability of nano‐TiO₂ powder and the stability of the TiO₂‐d‐PS materials were significantly enhanced through pretreatment, which was supported by the increase in the DCA when the nano‐TiO₂ was pretreated by the coupling agent. The results of SEM and EDS indicated that the nano‐TiO₂ dispersed homogeneously in the PS matrix. The pretreatment process is an effective way to break the aggregation of nano‐TiO₂, which was confirmed by TEM results. Melt blending is a feasible method to prepare PS doped high Z element ICF target materials.     

Electrical,optical and mechanical properties of PS/GNP composite films

In this study, the electrical, optical and mechanical properties of polystyrene (PS) thin films added graphene nanoplatelet (GNP) have been investigated. Surface conductivity (σ), absorbance intensity (A) and tensile modulus of these composite films have increased with increasing the content of GNP in the composite. The increase in the electrical and optical properties of the PS/GNP composite films has been interpreted by site and classical percolation theory, respectively. The electrical and the optical percolation thresholds of PS/GNP composite films were determined as R_σ?=?23.0?wt.% and R_op?=?13.0?wt.%, respectively. While the conductivity results have been attributed to the classical percolation theory, the optical results have attributed to the site percolation theory. The electrical (β_σ) and the optical (β_op) critical exponents were calculated as 2.54 and 0.40, respectively. The tensile modulus and the tensile strength of the PS/GNP composites increased with the increasing of GNP content in the PS. But, the toughness of the composites fluctuated with GNP addition.     

Investigation of microwave absorbing properties for magnetic nanofiber of polystyrene–polyvinylpyrrolidone

Aligned magnetic blend of polystyrene–polyvinylpyrrolidone (PS–PVP) nanofibers were prepared by this method. First, polystyrene–polyvinylpyrrolidone (PS–PVP) blend solution in THF was synthesized. Then magnetic of PS–PVP–Fe₃O₄–polyethylene glycol (PEG) was prepared by masking method. Finally, magnetic nanofiber of PS–PVP–Fe₃O₄–PEG was prepared by electrospinning method, too. An electric potential difference of 25 kV was applied between the collector and a syringe tip, and the distance between the collector and the tip was 13 cm. Fe₃O₄ is exhibit various magnetic properties of which the complex permeability and the permittivity, in particular, are important in determining their high frequency characteristics. The magnetic oxide particles and nanofiber of nanometer size were characterized by TEM and SEM respectively. The thermal properties of nanofibers were determined by TGA and DSC. The magnetic characterization of the fibers was also performed by VSM and AFM techniques. On the other hand, nanofiber with diameters ranging from 30 to 40 nm, showing at room temperature, coercive field values of around 25 kV and saturation magnetization was 1.1 emu/g. Microwave reflection loss of the sample was tested at 8–12 GHz microwave frequencies and the results showed that magnetic nanofiber possessed the microwave absorbing properties.     

Organo-modified magnesium hydroxide nano-needle and its polystyrene nanocomposite

Acrylic acid modified magnesium hydroxide nano-needles (AA–Mg(OH)₂) had been synthesized by alkaline injected into magnesium chloride solution at about 0°C in the presence of acrylic acid (AA). Then the polystyrene/magnesium hydroxide nano-needles composite (PS/Mg(OH)₂) had been prepared by the radical copolymerization with styrene in toluene system using AA–Mg(OH)₂ as a macro-monomer. The elemental analysis (EA) and Fourier transform infrared (FTIR) analyses show that the polystyrene had been grafted onto the surfaces of the nano-needles (AA–Mg(OH)₂). The nano-needles (AA–Mg(OH)₂) had better dispersibility in polystyrene matrix as observed by transmission electron microscope (TEM) analysis. The thermal behavior analysis results from the differential scanning calorimetry (DSC) indicated that the magnesium hydroxide nano-needles had lower thermal decomposition temperature than that of the polymer matrix and it is expected that the nano-needles prepared by the proposed method could be used as an environmental-friendly flame retardant.     

Solution-processed high-k thin films as a resistive switching for ReRAM applications

Resistive switching characteristics of solution-processed high-k thin films (HfO_x and TaO_x) were investigated for ReRAM applications. The thickness of solution-processed high-k thin films can be easily controlled by simple spin coating. We optimized the critical thickness of solution-processed HfO_x and TaO_x thin films, for reliable ReRAM operations. A similar bipolar resistive switching behavior was observed from both solution-processed and sputter-processed HfO_x films. Furthermore, it was found that the solution-processed HfO_x and TaO_x films have a uniform resistive switching characteristic. The dominant conduction of these solution-processed films is described by Ohmic conduction in the low-resistance state. On the other hand, Ohmic conduction at low voltage and Poole–Frenkel emission at high voltage dominate in the high-resistance state. It was verified that the solution-processed HfO_x and TaO_x films have superior endurance and retention characteristics. Therefore, ReRAM devices based on solution-processed high-k materials are expected to be a promising candidate, for usage of resistive memory in glass substrate or flexible substrate based electronic devices.     

Preparation of conductive nanocomposites based on poly (aniline-co- butyl 3-aminobenzoate) and poly (aniline-co-ethyl 3-aminobenzoate) by solution blending method

The polyaniline (PANI) is a widely studied conducting polymer due to its application in several devices such as biosensor, gas sensor etc. Known methods to produce PANI composites may be essentially reduced to two distinct groups: synthetic methods based on aniline polymerization in the presence of or inside a matrix polymer, and blending methods to mix a previously prepared PANI with a matrix polymer. Poly (aniline-co-butyl 3-aminobenzoate) (ANI-co-BAB) and poly (aniline-co-ethyl 3-aminobenzoate) (ANI-co-EAB) are prepared as conducting copolymers in nanoscale by chemical oxidation method under ultrasonic irradiation. The different molar ratio of aniline to butyl 3-aminobenzoate and ethyl 3-aminobenzoate are used in the preparation of copolymers. Conductive nanocomposites based on ANI-co-BAB or ANI-co-EAB with poly (styrene-alt-maleic acid) (PSMAC), and polystyrene are prepared by solution blending method. The obtained conductive composites formed films with good homogeneity and flexibility. The conductivity of the obtained nanocomposites is measured with a four-probe method. The electrical conductivity of the composites (ANI-co-EAB)/PSMAC/PS and (ANI-co-BAB)/PSMAC/PS are 24?×?10^?5?S?cm^?1 and 31?×?10^?5?S?cm, respectively. Our results show that the (ANI-co-BAB)/PSMAC/PS composite has more conductivity than (ANI-co-EAB)/PSMAC/PS composite. The copolymers and composites in nanoscale are characterized by FT-IR and ¹H NMR spectral data. The surface morphology was studied using SEM analysis. Also, their grain size is measured using XRD studies.     

Electrospinning fabrication and oxygen sensing properties of Cu(I) complex-polystyrene composite microfibrous membranes

In this paper, a phosphorescent Cu(I) complex of [Cu(POP)(ECI-Phen)]BF₄, where POP=bis[2-(diphenylphosphino)phenyl]ether, and ECI-Phen=1-ethyl-2-(N-ethyl-carbazole-yl-4-)imidazo[4,5-f]1,10-phenanthroline, is incorporated into a polystyrene matrix of polystyrene (PS) to form microfibers membranes. The possibility of using the resulted composite microfibrous membranes as an optical oxygen sensor is explored. Good linearity and short response time are obtained with a sensitivity of 9.8. These results suggest that phosphorescent [Cu(POP)(ECI-Phen)]BF₄ is a promising candidate for oxygen-sensors and PS is an excellent matrix for oxygen sensing material because it owns a large surface-area-to-volume ratio and can supply a homogeneous matrix for probe molecules. Further analysis suggests that the molecular structure of diamine ligand in Cu(I) complexes is critical for sensitivity due to the characteristic electronic structure of excited state Cu(I) complexes.     

Young’s modulus of PS/CeO<Subscript>2</Subscript> composite with core/shell structure microspheres measured using atomic force microscopy

Organic–inorganic composite microspheres with PS as a core and CeO₂ as a shell were synthesized by in situ chemical precipitation method. The size of PS core was 117, 163, 206, and 241 nm, respectively, and the shell thickness was about 10 nm. The CeO₂ shell was composed of a large number of nanoparticles, of which the size was 4–6 nm. Atomic force microscopy was employed to probe the mechanical properties of core–shell structured ceria-coated polystyrene (PS/CeO₂) composite microspheres. On the basis of Hertz’s theory of contact mechanics, compressive moduli were measured by the analysis of force–displacement curves captured on the microsphere samples. For a fixed CeO₂ shell thickness, the Young’s modulus of composite microspheres increased with an increase of PS core size. The calculated Young’s moduli (E) values of composites for 136, 185, 242, and 261 nm in diameter were 5.78 ± 0.9, 7.23 ± 1.3, 11.46 ± 1.7, and 14.54 ± 1.4 GPa, respectively. The results revealed the effect of the CeO₂ shell on the elastic deformation of the PS core. This approach will provide fundamental insights into the actual role of organic/inorganic core/shell composite abrasives in chemical mechanical polishing.     

Carbon materials with quasi-graphene layers: the dielectric, percolation properties and the electronic transport mechanism

We investigate the dielectric properties of multi-walled carbon nanotubes (MWCNTs) and graphite filling in SiO₂ with the filling concentration of 2-20 wt.% in the frequency range of 10²-10⁷ Hz. MWCNTs and graphite have general electrical properties and percolation phenomena owing to their quasi-structure made up of graphene layers. Both permittivity ε and conductivity σ exhibit jumps around the percolation threshold. Variations of dielectric properties of the composites are in agreement with the percolation theory. All the percolation phenomena are determined by hopping and migrating electrons, which are attributed to the special electronic transport mechanism of the fillers in the composites. However, the twin-percolation phenomenon exists when the concentration of MWCNTs is between 5-10 wt.% and 15-20 wt.% in the MWCNTs/SiO₂ composites, while in the graphite/SiO₂ composites, there is only one percolation phenomenon in the graphite concentration of 10-15 wt.%. The unique twin-percolation phenomenon of MWCNTs/SiO₂ is described and attributed to the electronic transfer mechanism, especially the network effect of MWCNTs in the composites. The formation of network plays an essential role in determining the second percolation threshold of MWCNTs/SiO₂.     

Flowability and Mechanical and Thermal Properties of Nylon 6/Ethylene bis-Stearamide/Carboxylic Silica Composites

Nylon 6 (PA 6)/ethylene bis-stearamide (EBS)/SiO₂- carboxylic acid-functionalized silica nanoparticles (COOH) composites were prepared by in-situ polymerization of caprolactam. SiO₂-COOH was used to enhance the compatibility between SiO₂ and PA 6 matrix. For comparison, pure PA 6 and PA 6/EBS composites were also prepared via the same method. The PA 6/EBS/SiO₂-COOH composites with low content of EBS and SiO₂-COOH had greater melt-flow index (MFI) (the value of MFI increased by 50%–80%) than the pure PA 6. The results of mechanical properties showed almost no decrease in the tensile strength of PA 6/EBS/SiO₂-COOH composites, with the bending strength decreasing by 17%–21%. However, the Izod impact strength of the PA 6/EBS/SiO₂-COOH composites was greatly improved compared with pure PA 6, which indicated that the toughness of PA 6/EBS/SiO₂-COOH had been greatly improved. The morphology of Izod impacted fractured surfaces of PA 6/EBS/SiO₂-COOH was observed by scanning electron microscopy. The results revealed that the PA 6/EBS/SiO₂-COOH composites presented a typical ductile fracture behavior with large amounts of long and large strip-like cracks. When the content of SiO₂-COOH was 0.2 wt%, the SiO₂-COOH particles were uniformly dispersed over the entire body of the PA 6 matrix. The results from differential scanning calorimetry indicated that the melting point (T_m), degree of crystallinity (X_c), and crystallization temperatures (T_c) of PA 6/EBS/SiO₂-COOH composites were lower than the pure PA 6.     

Use of flow microcalorimetry and dynamic mechanical thermal analysis for probing interphase structure in poly(styrene-b-butadiene-b-styrene)/magnesium hydroxide composites

Interactions between magnesium hydroxide (Mg(OH)₂ particles (both untreated and treated with 16-methyl heptadecanoic acid (isostearic acid)) and low molar mass poly(styrene) (PS) and poly(butadiene) (PB) have been studied by flow microcalorimetry (FMC) and have been related to the interphase structure in poly(styrene-b-butadiene-b-styrene) (SBS)/Mg(OH)₂ composites using dynamic mechanical thermal analysis (DMTA). The FMC studies revealed that both polymers adsorbed strongly onto an untreated magnesium hydroxide surface though the PB showed greater irreversible adsorption from the heptane carrier fluid. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) studies on filler samples removed from the FMC cell after the adsorption-desorption cycle confirmed strong polymer filler interaction. Adsorption of the low molar mass samples of PS and PB onto a pre-adsorbed monolayer of isostearic acid on Mg(OH)₂ resulted in a very significant reduction in polymer adsorption activity due to blockage of adsorption sites. DMTA studies revealed that strong adsorption of PS and PB blocks of SBS onto untreated filler in composites containing 60% w/w Mg(OH)₂ gave rise to phase mixing that led to an 18 °C reduction in the T _g of the PS phase relative to that in the unfilled matrix. However, in equivalent composites based on isostearic acid treated filler a smaller reduction (10 °C) was observed, therefore reflecting reduced filler-matrix interaction and reduced phase mixing.     

Bonding at Compatible and Incompatible Amorphous Interfaces of Polystyrene and Poly(Methyl Methacrylate) Below the Glass Transition Temperature

Abstract

Films of high‐molecular‐weight amorphous polystyrene (PS, M _w = 225 kg/mol, M _w/M _n = 3, T _g‐bulk = 97°C, where T _g‐bulk is the glass transition temperature of the bulk sample) and poly(methyl methacrylate) (PMMA, M _w = 87 kg/mol, M _w/M _n = 2, T _g‐bulk = 109°C) were brought into contact in a lap‐shear joint geometry at a constant healing temperature T _h, between 44°C and 114°C, for 1 or 24 hr and submitted to tensile loading on an Instron tester at ambient temperature. The development of the lap‐shear strength σ at an incompatible PS–PMMA interface has been followed in regard to those at compatible PS–PS and PMMA–PMMA interfaces. The values of strength for the incompatible PS–PMMA and compatible PMMA–PMMA interfaces were found to be close, both being smaller by a factor of 2 to 3 than the values of σ for the PS–PS interface developed after healing at the same conditions. This observation suggests that the development of the interfacial structure at the PS–PMMA interface is controlled by the slow component, i.e., PMMA. Bonding at the three interfaces investigated was mechanically detected after healing for 24 hr at T _h = 44°C, i.e., well below T _g‐bulks of PS and PMMA, with the observation of very close values of the lap‐shear strength for the three interfaces considered, 0.11–0.13 MPa. This result indicates that the incompatibility between the chain segments of PS and PMMA plays a negligible negative role in the interfacial bonding well below T _g‐bulk.     

Bulk magnetization and 1H NMR spectra of magnetically heterogeneous model systems

Bulk magnetization and ¹H static and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of two magnetically heterogeneous model systems based on laponite (LAP) layered silicate or polystyrene (PS) with low and high proton concentration, respectively, and ferrimagnetic Fe₂O₃ nano- or micro-particles have been studied. In LAP+Fe₂O₃, a major contribution to the NMR signal broadening is due to the dipolar coupling between the magnetic moments of protons and magnetic particles. In PS+Fe₂O₃, due to the higher proton concentration in polystyrene and stronger proton–proton dipolar coupling, an additional broadening is observed, i.e. ¹H MAS NMR spectra of magnetically heterogeneous systems are sensitive to both proton–magnetic particles and proton–proton dipolar couplings. An increase of the volume magnetization by ～1 emu/cm³ affects the ¹H NMR signal width in a way that is similar to an increase of the proton concentration by ～2×10²²/cm³. ¹H MAS NMR spectra, along with bulk magnetization measurements, allow the accurate determination of the hydrogen concentration in magnetically heterogeneous systems.     

Preparation of PS/TiO2 as a white pigment for electrophoretic displays

PS (polystyrene)/TiO₂, TiO₂ coated onto PS by a hydrolysis reaction, was prepared as a white pigment for electronic paper (e-paper). Two key parameters, density and zetapotential, were precisely controlled for use as a white pigment. The density was manipulated by changing the mixture ratio of EtOH to H₂O, and the concentration of titanium tetrabutoxide (TBO) in the hydrolysis reaction. The modification of PS/TiO₂ with (3-aminopropyl)triethoxy silane (APTES) and acetic acid showed positive zetapotential originated from the mutual effects between an amino functional group in APTES, and a proton from acetic acid. The mutual effect was studied, and PS/TiO₂ with density of 1.6 g/cm² and zetapotential of 75 mV was prepared using the results.     

CORRELATION BETWEEN MORPHOLOGY AND MECHANICAL PROPERTIES OF DIFFERENT STYRENE/BUTADIENE TRIBLOCK COPOLYMERS: A SCANNING FORCE MICROSCOPY STUDY*

The morphology of different styrene/butadiene (SB) block copolymers with triblock architectures was investigated using tapping mode scanning force microscopy (SFM). Comparative analysis of the morphology of the samples at the polymer/substrate interface of solution-cast films and in bulk was performed. It was found that, besides the total phase volume ratio, the interfacial structure between the incompatible chains determines the phase morphology and mechanical properties of the investigated block copolymers. The asymmetric SBS triblock copolymer (φ_ps( 74 vol%) forms, as expected, a cylindrical morphology with hexagonally packed polybutadiene (PB) cylinders in the polystyrene (PS) matrix. Depending on the interfacial structure, block configuration, and the hard/soft phase ratio, other triblock copolymers (φ_ps( 74 vol% and 65 vol%) show lamellae and randomly distributed PS cylinders in a random styrene/butadiene copolymer S/B matrix, respectively.

     

Effect of particle size of graphites on electrical conductivity of graphite/polymer composite

The effect of particle size of graphite particles on the dispersion state of graphite particles and electrical conductivity of graphite/low-density polyethylene (LDPE) composites is investigated. Graphite particles which have plate-like and spherical shapes and mean particle sizes of 2.1 to 82.6 μm are used. Scanning electron microscopy observation showed that graphite particles are not aggregated and ordered along the direction of mixing-roll in the polymer matrix. X-ray diffraction measurements show that crystallite size of the (110) plane of polyethylene crystal and the crystallinity are significantly affected by the particle size of graphite particles. These results were interpreted as due to the orientation of PE crystallites. The electrical conductivity of composites changes discontinuously at the critical volume fraction of particles, Ø_c. The Ø_c values given by the percolation equation increase with decreasing of the particle size of graphites. The plate-like graphite particles with a mean particle size of 2.1 μm could induce conductivity at Ø_c of 0.135. The values of Ø_c increased linearly with increasing of the mean particle sizes of the plate-like graphites. The value of Ø_c of spherical graphite particle is the largest value, 0.292, in all specimens.