ABSTRACT:We investigated, on the basis of light-scattering theory, the relationship between the color of polypropylene gel and the refractive index in the vicinity of the interface of polypropylene networks in the gel when prepared at different cooling temperatures after dissolving the polypropylene at 160• C. The color of the gels was found to differ depending on the cooling temperature upon gel formation. SEM images of these gels showed polypropylene networks with smaller diameters with decreases in the cooling temperature. Based on measurements using the maximum transmittance method, it was found that the origin of color changes in the gels is a shift in the wavelength dispersion of the refractive index for polypropylene to a higher refractive index. Changes in the solvent content of polypropylene in the gels, which were evaluated using experimental values of the refractive indices and densities for the solvent and polypropylene, revealed that the solvent causes swelling of the polypropylene interface which is a source of light-scattering. The degree of swelling appears to depend upon the cooling temperature when gels are prepared by cooling beyond the glass transition temperature of polypropylene. KEY WORDS Coloration / Thermochromism / Polypropylene / Xylene / Surface / Wavelength Dispersion of Refractive Index /
ABSTRACT:The coloration of polypropylene gel was investigated by light scattering theory, in which wavelength dispersion of refractive indices for polypropylene and solvent is particularly noted. The coloration and thermochromic phenomena of polypropylene gel were concluded to be caused by the selective light scattering from size-controlled polypropylene networks with a solvent, that have the same refractive index as that of polypropylene at a certain wavelength in the visible region, but with degree of wavelength dispersion larger than that of polypropylene, since maximum transmittance wavelength in transmittance spectra of the gels obtained experimentally is in fair agreement with that estimated from wavelength dispersion curves of refractive indices of solvent and polypropylene obtained from independent experiments. The change of the transmittance spectra at a definite temperature with the elapse of time reflects change of the refractive index in the vicinity of the interface of polypropylene network in the gel prepared under confinement and change of the interface structure of the polypropylene networks in the gel.KEY WORDS Coloration I Thermochromism /Polypropylene/ Xylene/ Wavelength Dispersion of Refractive Index
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