Tamaki Naganuma

Effects of the difference between the refractive indices of constituent materials on the light transmittance of glass-particle-dispersed epoxy-matrix optical composites

Abstract Glass particles with a size d p of 38–53 μm are incorporated into a clear epoxy matrix and the light transmittance T L of the composites is measured in the wavelength γ range from 200 to 1100 nm. The net difference ▵n c between the refractive indices of the glass particles and the matrix of the fabricated composite ranged from nearly zero to 0.03. This difference between the refractive indices is achieved by, firstly, selecting the optical properties of dispersed glass particles and secondly, changing the thermal stress in the composite. The effect of the difference ▵n c between the refractive indices of the glass particles and the epoxy matrix on the light transmittance of the composite is obtained. It is found that the light transmission spectrum of the composite is correlated with the relationship between the wavelength dispersion curves of the refractive indices of the glass particles and the matrix. At a fixed wavelength, the T L−▵n c curve is only dependent on the particle size and volume fraction. The measured T L−▵n c curves of the composite at a given particle volume fraction and a given particle size show that the maximum light transmittance of the composite appears when ▵n c ≈ 0. The value is about 92% and is nearly the same as that of the pure epoxy matrix.

Fabrication of transparent continuous oxynitride glass fiber-reinforced glass matrix composite

Unidirectional-aligned continuous SiCaAlON fiber-reinforced glass matrix composites have been fabricated and their light transmittance was measured. Optically transparent composites with the fiber volume fraction from 0.03 to 0.10 were fabricated by a hot-pressing method. The light transmittance of the composite perpendicular to the fiber axis in the wavelength range from 200 to 700 nm was measured, and found to decrease with the increase of the fiber volume fraction. This decrease is explained by the theory proposed by the authors (Hl and YK). The major source of a light transmittance loss of the composite originates from a phase change of transmitted light in the composite.

Optothermal properties of glass particle-dispersed epoxy matrix composite

Optically transparent polymers are required for the packaging of advanced optoelectric devices; if such materials are available, the communication between the outside and inside devices at near IR light (λ≈ 800 nm) becomes possible. The minimum of the required material properties for the packaging materials are (i) optical transparency at near IR wavelength region and (ii) thermal expansion coefficient close to optoelectronic devices. An epoxy material is one of the strong candidates because the material possesses good optical properties and easy to apply conventional packaging processes. However, the thermal expansion coefficients of epoxy materials are one order larger than those of optoelectronic devices and this thermal expansion mismatch induces severe damage under service condition. Thus, the pure epoxy material could not be used as the packaging material even though its light transmittance is in the required range. The incorporation of glass particles is one of the solutions to reduce the apparent thermal expansion coefficient of epoxy materials, however. The light transmittance after the incorporation is usually lost by the difference between the refractive index of the particle and that of epoxy matrix. Recently, a composite material, which has both an optical transparency and a low thermal expansion coefficient, was reported [1, 2]. The report proved that when the refractive index difference was reduced to the order of 10−3, optical transparency appears in the composite. Theoretical consideration also demonstrates a procedure for the selection of fiber and matrix to achieve optical transparency after the incorporation of a glass fiber into an epoxy matrix [3]. Reports also demonstrated the effect of refractive index difference on the light transmittance [4] and particle size on the light transmittance [5]. However, the relation between the light transmittance and thermal expansion coefficient of the glass particle-dispersed optically transparent epoxy matrix composites is not yet reported. The purpose of this paper is to show the guideline for the property design in light transmittance and thermal expansion coefficient of glass particledispersed epoxy matrix composites. Two different size glass particles were used. The particle had an average diameter of dp= 26 and 85μm. It should be noted that the size of the glass particles was much larger than the wavelength of light in the visible wavelength region. The chemical composition of the glass particle was SiO2 (60 wt %), Al2O3 (17.4 wt %),

Effect of electrical resistivity of Si-Ti-C-O fiber on electromagnetic wave penetration depth of short fiber-dispersed composites

High frequency electromagnetic wave has been used for various environments and has especially been required for the fields of advanced wireless communication systems. The system requires electromagnetic wave absorbing material as well as electromagnetic wave reflecting and transmitting materials. Among existing electromagnetic wave absorbing materials, a Si-Ti-C-O base ceramic fiber (Tyranno©R, Ube Industries, Ltd., Yamaguchi, Japan) reinforced polymer matrix composite is expected to have high specific modulus, high specific strength and electromagnetic wave absorbing properties [1, 2]. Recent development of this Si-Ti-C-O fiber allow a wide range of electrical resistivity to be obtained; the electrical resistivity of the fiber has a range from 10−3 to 104 m [3]. However, the effect of fiber electrical resistivity on electromagnetic wave absorbing potential of a composite has not been studied in depth. The present study has been focused on the effect of the electrical resistivity of Si-Ti-C-O fiber on the penetration depth of the short Si-Ti-C-O fiber-dispersed epoxy matrix composites. The chemical composition (at%) of the original Si-Ti-C-O fiber was Ti: 0.78, C: 44, O: 21 and the remainder was Si [1, 3]. The fiber has a circular crosssection with a diameter of 8.5–13 μm and a ∼50 nm carbon-rich layer beneath the surface [4]. Properties of the fiber are listed in Table I [3]. As a received continuous Si-Ti-C-O fiber bundle was mechanically cut into chopped fibers with an average length of ∼2.5 mm. The epoxy matrix was prepared from the mixture of epoxy monomer, hardener, and accelerator, details of the starting materials were reported elsewhere [5–7]. The chopped Si-Ti-C-O fibers were put into the mixture of the components and mixed mechanically. To obtain suitable electrical resistivity of the composite using the percolation effect [8] of the chopped fibers, the mixing was continued for 30 min. This processing condition was selected following a preliminary study of the same composite material [2]. Then, the fiber-epoxy mixture was degassed, poured into a Teflon©R-coated mold and slightly pressed, and thereafter was cured in ambient air at 373 K for 4 h in an oven. The fiber volume fraction in the composite was controlled by the weight ratio of the fiber and matrix. The fiber volume fraction was fixed at 5 vol%. A typical polished section of the composites

Effect of total particle surface area on the light transmittance of glass particle-dispersed epoxy matrix optical composites

The effect of particle volume fraction f p on the light transmittance of glass particle-dispersed epoxy matrix composites with a particle volume fraction of f p = 0.0001 to 0.4 was studied. The particle size used was much larger than the wavelength of light in a visible wavelength. The transmitted laser beam scattering pattern and light transmittance of the composites were obtained, and the transmitted laser beam pattern showed a broadening, which increased with an increase in particle volume fraction. This behavior appeared more remarkable in particles with smaller diameters. The light transmittance of the composite was affected by the particle volume fraction f p and was divided into two characteristic regions according to f p . For f p f p > 0.01 was strongly affected by f p and size of the glass particle d p . The effects of f p and d p on the light transmittance are explained by the introduction of a normalized total surface area 〈 S〉 A guideline to obtain higher light transmittance of the composite is discussed based on the parameter 〈S 〉.

Spatial spreading behavior of transmitted light from glass particle-dispersed epoxy matrix composites

The spatial spreading behavior of glass particle-dispersed epoxy matrix optical composites has been observed, and the composites used have light transmittance in the visible wavelength region. The effect of (i) particle volume fraction, (ii) particle size and (iii) refractive index difference between the particle and matrix on the spreading behavior are discussed. The spatial spreading behavior of transmitted light from a back surface of the composites is found to be strongly correlated with light scattering behavior of the composite. The increase of spatial light spreading also increases spatial light transmittance of the composite.