TAGRA 2025

Dynamic Light Scattering (DLS), also known as photon correlation spectroscopy or quasi-elastic light scattering, is a widely used technique for characterizing nanoparticle size, size distribution, and aggregation behavior in dispersions, making it essential for nanofluid research engineered colloidal suspensions of nanoparticles in base fluids such as water, ethylene glycol, or oils. The thermophysical properties of nanofluids, including thermal conductivity, viscosity, optical characteristics, and stability, are strongly influenced by particle size and dispersion quality, with minor variations potentially causing aggregation or sedimentation. DLS measures fluctuations in scattered light intensity due to Brownian motion, from which the diffusion coefficient is obtained and converted to a hydrodynamic diameter via the Stokes–Einstein equation. This hydrodynamic size accounts for primary particles, aggregates, solvation layers, and surfactant coatings, providing insight into real dispersion conditions. DLS is widely applied to assess colloidal stability, detect aggregation, monitor zeta potential, and perform time-dependent studies under storage or operational stresses, guiding the optimization of surfactants, pH, ionic strength, and preparation methods. It also evaluates the effectiveness of nanofluid synthesis techniques such as ultrasonication, high-shear mixing, and one-step versus two-step approaches. Correlating DLS-derived particle size distributions with thermophysical properties enables the design of nanofluids with predictable performance. Modern instruments allow in-situ monitoring under controlled temperature, flow, or shear conditions, simulating practical operating environments. Despite its advantages, DLS has limitations for highly polydisperse, concentrated, or non-spherical particle systems, necessitating complementary techniques like TEM, SEM, AFM, or nanoparticle tracking analysis for validation. Overall, DLS serves as a critical diagnostic tool, linking nanoscale particle behavior to the macroscale performance of nanofluids.