Now we can start to look at light scattering. In this first investigation we want to find out how many of the large TiO2 particles we have to add to the paint to make it optically dense, i.e. independent of the substrate.
The bottom interface is set to be a perfect absorber again. As shown in the tests before, the detector signal is 4% (due to the specular reflectance of the air-resin interface) if the volume fraction of the TiO2 spheres is 0. We now slowly increase the volume fraction, compute spectra in the range 300 ... 1000 nm with 7 points (we do not need spectral resolution in this case) and collect the results with the Collect program.
Starting at a volume fraction f = 0.01 a side view shows what happens:
The rays travel through the whole resin layer. Due to the pronounced forward scattering many of the rays that get scattered nevertheless reach the absorbing bottom. Consequently the detector signal is not too high yet:
At f = 0.2 almost no particles reach the bottom interface:
The diffuse reflectance signal is much higher now:
The next graph summarizes the results for various volume fractions:
