Coherent reflection of light from a turbid suspension of particles in an internal-reflection configuration: Theory versus experiment

Abstract

We compare a recently developed coherent-scattering model for the reflectance of light from a turbid colloidal suspension of particles with experimental measurements. The experimental data were obtained in an internal reflection configuration around the critical angle using a glass prism in contact with a monodisperse colloidal suspension of latex particles, and a polydisperse suspension of TiO2 particles. First, we review the coherent scattering model and extend it to the case of polydisperse suspensions in an internal reflection configuration. The experimental data is then compared with results of the coherent scattering model and results obtained assuming that the colloidal system can be treated as a homogeneous medium with an effective index of refraction. We find that the experimental results are not compatible with the effective medium model. On the other hand, good fits to the experimental curves can be obtained with the coherent scattering model.

Refractive index investigation of poly(vinyl alcohol) films with TiO2 nanoparticle inclusions

“…It is worth noting that some authors [23] propose theoretically even parabolic behavior of the effective permittivity particle concentration dependence of particle-filled composites for the f < 0.1, in case of the inclusion permittivity of about 100. This case is very close to the TiO 2 nanoparticles, whose permittivity is reported to be 86 at 1.0 MHz [24].…”

Accuratein situmeasurement of complex refractive index and particle size in intralipid emulsions

“…3.2) the density of scatterers encountered near the surface may be slightly different from the density that exists in the bulk. 20 A third fitting parameter may be employed to model the slight departure from the bulk value of the complex refractive index within a thin layer (of thickness equal to the particle diameter) at the surface, but we have chosen not to do so in this work. )…”

“…It is noteworthy that, despite all the attention, a precise in situ determination of several important optical properties of intralipid emulsions, such as the particle size, refractive index, and attenuation coefficient (which is commonly expressed as the imaginary part of a complex refractive index [13][14][15][16][17][18][19][20][21] ), has continued to elude researchers. 28 The chief difficulty arises from the fact that intralipid emulsions, being highly turbid, have a large attenuation coefficient.…”

“…However, the most widely used reflectance-based method, which equates the point of maximum slope of the reflectance-versus-incident-angle curve with an effective critical angle, 3,[13][14][15]21 has been shown to be significantly inaccurate even after error-correction is attempted. 29 Other attempts to extract the complex refractive index by modeling the reflectance data either introduce extraneous fitting parameters (beyond the two parameters of interest, namely, the real and imaginary parts of the refractive index) resulting in overfitting of the data 19,20 or focus on only the critical angle region, which is just a small subset of the reflectance data. [14][15][16][17][18] .…”

“…16,17, and 18 where a small subset of the reflectance curve was focused on and previous works 5,14,15,20 where just ∼20 data points were fitted, here we fit the entire reflectance curve comprising ∼1000 data points. In further contrast to previous works 5, [19][20][21] we employ no other fitting parameters besides the two variables we seek to determine-the real and imaginary parts of the refractive index-thus avoiding ambiguity in the extracted values owing to overfitting. To the best of our knowledge, this is the first case where the entire reflectance-versus-incident-angle data-curve, spanning both TIR and non-TIR regimes, has been accurately described by a theoretical model for any highly turbid medium.…”