Comparison of atomic force microscopy and dynamic light scattering on the size characterization of surfactant-modified WC/Co nanoparticles dispersed in aqueous media

Tungsten carbide cobalt nanoparticles (WC/Co NPs) are extensively employed to fabricate wear-resistant parts, cutting tools, and rock drills. The colloidal stability of the WC/Co NP suspension plays a vital role in determining the mechanical properties of WC/Co-based products. In this work, dispersion of WC/Co NPs in aqueous media was conducted using surfactants (cationic, anionic, nonionic) with different concentration conditions. The z-average hydrodynamic diameters measured using dynamic light scattering (DLS) revealed the optimal surfactant for WC/Co NP dispersion: cationic hexadecyltrimethylammonium bromide (CTAB) which induces interparticle electrostatic repulsion forces at a concentration of 2 g/L. The capping behavior of CTAB was demonstrated using Zeta-potential analysis, Fourier transform infrared spectroscopy, and X-ray diffraction measurements. The mean size measurement of immobilized WC/Co NPs was also conducted using atomic force microscopy (AFM). We demonstrate a comparative protocol between number-weighted mean sizes measured using AFM (d_AFM) and DLS (d_DLS) in relation to the relative standard deviation (RSD) from AFM measurements. A highly linear correlation was demonstrated between d_DLS/d_AFM and RSD. We indicate that for polydisperse (RSD > 0.1) and non-spherical NPs, the highest correlation between d_DLS and d_AFM exists when the RSD is 0.37, where d_DLS/d_AFM is close to 1.