Effect of total particle surface area on the light transmittance of glass particle-dispersed epoxy matrix optical compos
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The effect of particle volume fraction fp on the light transmittance of glass particle-dispersed epoxy matrix composites with a particle volume fraction of fp ⳱ 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 fp and was divided into two characteristic regions according to fp. For fp < 0.01, the light transmittance was slightly affected by the incorporation of the particles, while the light transmittance of the composite with fp > 0.01 was strongly affected by fp and size of the glass particle dp. The effects of fp and dp 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〉.
I. INTRODUCTION
Optically transparent composite materials (hereafter called optical composites) such as short SiCaAlON-fiber glass matrix composite,1,2 glass fiber-reinforced polymer matrix,3,4 and glass particle-dispersed polymer matrix composites5–9 have been developed and are believed to possess both light transmittance and additional properties; these additional properties without light transmittance are usually achieved by incorporation of a second phase into matrix materials. The glass particle-dispersed epoxy matrix composite is able to acquire both properties of low thermal expansion and high light transmittance9 and therefore is expected to be applicable to a package of optoelectronic devices, which require light transmittance. The thermal expansion coefficient of the glass particle-dispersed epoxy matrix composite is easily tailored; however, the tailoring of optical properties is difficult. This is because the optical properties are highly dependent on various factors, such as the difference in refractive index between constituent materials, light absorption, and the geometrical factor of the composed particles for the demanded materials. Previous studies5–10 showed that the incorporation of a glass particle creates an additional light-scattering source, and evidence of the a)
Address all correspondence to this author e-mail: [email protected] J. Mater. Res., Vol. 17, No. 12, Dec 2002
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light-scattering by a particle on the light transmittance of an optical composite has recently been clearly demonstrated using a pico second-order pulse.10 The report showed that light transmittance of the composites was correlated with the broadening of the transmitted pulse profile, which originates from multiple light scatterings. The close matching of the refractive index between par
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