In this article we report experimental and theoretical results of angle-dependent laser light scattering of nano titanium dioxide nucleated on silica particles. It was observed that the experimental scattering profile from nano-titania coated silica (TCS) particle resembles that of a Rayleigh scattering. It can be inferred from the light scattering profile that nucleating fine particles onto a surface of a bigger particle (core), the resulting scattering profile is dominated by the smaller particles. Thin film transmittance measurement of TCS particles also supports this claim. The theoretical scattering predictions do not match with the experimental findings and the reasons for the discrepancies are addressed. This Rayleigh-like scattering property of TCS particles can be used in cosmetic formulations as a replacement for nanoparticles to provide protection from harmful ultraviolet rays. This study helps to provide insights into these systems for their potential usage in cosmetics.
The rather low scattering or extinction efficiency of small nanoparticles, metallic and otherwise, is significantly enhanced when they are adsorbed on a larger core particle. But the photoabsorption by particles with varying surface area fractions on a larger core particle is found to be limited by saturation. It is found that the core-shell particle can have a lower absorption efficiency than a dielectric core with its surface partially nucleated with absorbing particles-an "incomplete nanoshell" particle. We have both numerically and experimentally studied the optical efficiencies of titania (TiO2) nucleated in various degrees on silica (SiO2) nanospheres. We show that optimal surface nucleation over cores of appropriate sizes and optical properties will have a direct impact on the applications exploiting the absorption and scattering properties of such composite particles.
The iridescence phenomenon of C12-alkenylsuccinic acid (ASA) is a result of the coherent reflection of light from periodically ordered alternating lamellar surfactant stacks and solvent molecules. Here we report the effect of cationic, anionic, and nonionic surfactants on the iridescence of ASA. It was observed that ionic surfactants resulted in destabilization of the iridescence of ASA, while the addition of nonionic surfactant stabilized the system. The nature of the interactions of these surfactants on ASA was investigated using reflectance spectroscopy, differential scanning calorimetry, optical microscopy, and small angle X-ray scattering (SAXS). The bilayer thickness was determined using reflectance spectra, SAXS, and theoretical calculations. It was observed that the nonionic surfactant does not alter the lamellar spacing of ASA, while ionic surfactant was seen to lower it by creating water-filled defects. The diffraction patterns also exhibit an additional broad peak which indicates formation of uncorrelated bilayers. This study thus provides understanding of such swollen lamellar systems.
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