Pinhole mirror-based ultra-small angle light scattering setup for simultaneous measurement of scattering and transmission

An ultra-small angle light scattering setup with the ability of simultaneous registration of scattered light by a charge-coupled device camera and the transmitted direct beam by a pin photodiode was developed. A pinhole mirror was used to reflect the scattered light; the transmitted direct beam was focused and passed through the central pinhole with a diameter of 500 μm. Time-resolved static light scattering measurement was carried out over the angular range 0.2° $≤θ≤$ 8.9° with a time resolution of ∼33 ms. The measured scattering pattern in the q-range between 5 × 10⁻⁵ and 1.5 × 10⁻³ nm⁻¹ enables investigating structures of few micrometers to submillimeter, where q is the scattering vector. A LabVIEW-based graphical user interface was developed, which integrates the data acquisition of the scattering pattern and the transmitted intensity. The Peltier temperature-controlled sample cells of varying thicknesses allow for a rapid temperature equilibration and minimization of multiple scattering. The spinodal decomposition for coacervation (phase separation) kinetics of an aqueous mixture of oppositely charged polyelectrolytes was demonstrated.