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| Refractive index of polystyrene | Prev topic | Next topic Fig. 1 Table 1 |
Polystyrene microspheres are widely used in light scattering experiments and in simulations of light scattering media such as human tissue. Hence the importance of the refractive index of polystyrene which has been studied by several research groups (Table 1).
Chen et al (2003) used, in a wavelength range of 275 to 390 nm, the following Cauchy equation for the real part of the refractive index (Fig. 1, top panel), based on the work of Matheson and Saunderson (1952):
| m' (λ) = ∑i = 0 to 2 |
|
(1) |
where ai = 1.5663, 7.85e3 nm2, and 3.34e8 nm4 for i = 0, 1, and 2 respectively, and λ [nm] is the wavelength of light in vacuum. As shown in Fig. 3 of Ma et al (2003) this formulation agrees well with more recent measurements of Nikolow and Ivanov (2000).
Strain induced by confining material to a microsphere is believed to modify the refractive index through the photoelastic effect (for example, Ma et al 2003). This prompted recent measurements of the complex refractive index of polystyrene (Fig. 1) as micometer-sized spheres (diameter = 0.966 µm) by Ma et al (2003), who used Monte Carlo modeling of radiative transfer in turbid media to interpret results of measurements of absorption and attenuation of light by polystyrene microsphere suspensions in the visible and near-infared. Ma et al fitted Eq. 1 to their data and obtained the following coefficients: ai = 1.5725, 3.1080e3 nm2, and 3.4779e8 nm4 for i = 0, 1, and 2 respectively, for a wavelength range of 390 to 1310 nm (Fig. 1, top panel).
Although in the UV and visible parts of the electromagnetic spectrum Eq. 1 yields the real part, m', of the refractive index of polystyrene significantly greater (~10 SD) than that derived by Ma et al (2003) for polystyrene microspheres, it provides values of m' approximately within the experimental error of the latter data in an infrared wavelength range of 860 to 1580 nm (Fig. 1, top panel).
Chen et al (2003) note a divergence in the experimental results for the imaginary part of the refractive index of polystyrene in the UV and propose the following approximation, based on the absorption data of Li et al (1991):
| m" (λ) = λα / (4π) [ 1 - √( |
|
)] | (2) |
in the UV, where α = 5e-4 nm-1, λ0 = 275 nm, and λ1 = 320 nm (Fig. 1, bottom panel). At λ = 275 nm, this gives m" ~ 0.011.
| CITATION: Jonasz M. 2006. Refractive index of polystyrene (www.tpdsci.com/Tpc/RIPolystyrene.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 23-Feb-2006 Modified: 05-Oct-2006 Peer-reviewed: 05-Oct-2006 |
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