High refractive index films of polymer nanocomposites

Abstract

Solutions of PbS particles and gelatin were used for the preparation of nanocomposites by a spin-coating process. This allows for the preparation of nanocomposite films with controlled thickness, e.g., between 40 nm and 2 /mm for a film containing 45 wt. % PbS. Surface roughness and film thickness were investigated by surface profilometry and scanning electron microscopy (SEM). The refractive index at 632.8 nm can be expressed by a linear function of the volume fraction of PbS in the range of 0 to 55 vol. % PbS. In this range, the refractive index increases from 1.5 to 2.5 with increasing PbS ratio and belongs, therefore, to the highest refractive indices known for polymeric composite materials.

High Refractive Index Si/SiOx Based Nanocomposites

“…[30] Gelatin and poly(ethyleneoxide) have been extensively used for the fabrication of high refractive index nanocomposites with PbS. [6][7][8] The multiple functional sites in gelatin, a denatured protein, and its solubility in polar protic solvents such as water and ethanol makes it a matrix of choice for the fabrication of silicon based nanocomposites. Mixing an aqueous solution of gelatin with the ethanolic suspension of Si nanoparticles and concentrating by bubbling N 2 , a viscous brown liquid was obtained.…”

“…[1][2][3] The need for high refractive index materials that readily conform to the elaborate structures proposed for photonic band-gap structures, [4,5] have attracted considerable attention in high loading nanocomposites. [6][7][8] The potential benefits in generating materials that gradually bridge the large refractive index gap between organics and inorganics along with maintaining reduced absorption and scattering, could benefit an array of photonic devices by improving the optical-coupling efficiencies between semiconductors and plastics or glass. [9] For example, the refractive indices of polymers vary between 1.3 and 1.7, while those of inorganic semiconductors vary between 2 and 5.…”

“…Inorganic high band-gap materials, such as TiO 2 , could reach up to refractive indices of 2.9 in their crystalline state, but above this limit it is necessary to consider composites of inorganic semiconductors such as those presented in Table 1. [10] High refractive index nanocomposites of PbS nanoparticles in gelatin or polyethylene oxide have been thoroughly investigated by Suter et al [6][7][8] Their studies indicate that both PbS particle size and loading influence the overall refractive index of the nanocomposite. Very small particles show reduced refractive index as compared to that of particles with diameter equal or greater than 25 nm which approach the refractive index of bulk PbS.…”

High Refractive Index Materials of Iron Sulfides and Poly(ethylene oxide)

“…It may be expected that the refractive index increases with increasing fraction of inorganic filler, 5,7,28,29 and that it is, therefore, favorable to prepare composites with low polymer content, i.e., a polymer content just sufficient to obtain a "soft" material. However, the results do not show the expected refractive index dependence (within the experimental precision).…”

“…Nanocomposites with extremely high or low refractive index have been prepared recently by coprecipitation or spin-coating from aqueous solutions. [4][5][6][7] The high refractive index nanocomposites consist of colloidal lead sulfide embedded in a polymer matrix. Due to the high refractive index of PbS, that of the composites is up to 3, over a broad wavelength range, and to our knowledge by far the highest reported for a polymer composite.…”