Analysis of dependent scattering mechanism in hard-sphere Yukawa random media

TL;DR

This paper investigates how structural correlations in hard-sphere Yukawa random media influence optical scattering, revealing that charge screening and packing density significantly affect dependent scattering mechanisms in colloidal suspensions.

Contribution

It extends the understanding of dependent scattering by analyzing the impact of structural correlations in Yukawa media, especially in charged colloids, using a recent theoretical framework.

Findings

Structural correlations significantly affect optical properties in charged colloids.

Salt concentration mainly influences packing-density-dependent screening effects.

Far-field interference dominates in low-refractive-index colloids.

Abstract

The structural correlations in the microscopic structures of random media can induce the dependent scattering mechanism and thus influence the optical scattering properties. Based on our recent theory on the dependent scattering mechanism in random media composed of discrete dual-dipolar scatterers (\textit{Physical Review A 97, 023836}), in this paper, we study the hard-sphere Yukawa (HSY) random media, in order to further elucidate the role of structural correlations in the dependent scattering mechanism and hence optical scattering properties. Here, we consider charged colloidal suspensions, whose effective pair interaction between colloids is described by a screened Coulomb (Yukawa) potential. By means of adding salt ions, the pair interaction between the charged particles can be flexibly tailored and therefore the structural correlations are modified. It is shown that this strategy can affect the optical properties significantly. For colloidal $\mathrm{TiO_2}$ suspensions, the modification of electric and magnetic dipole excitations induced by the structural correlations can substantially influence the optical scattering properties, in addition to the far-field interference effect described by the structure factor. However, this modification is only slightly altered by different salt concentrations and is mainly because of the packing-density-dependent screening effect. On the other hand, for low refractive index colloidal polystyrene suspensions, the dependent scattering mechanism mainly involves the far-field interference effect, and the effective exciting field amplitude for electric dipole almost remains unchanged under different structural correlations. The present study has profound implications for understanding the role of structural correlations in dependent scattering mechanism.