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 zaverage 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.