Determining the dispersion stability of black phosphorus colloids by 3D light scattering

Abstract

Understanding the dispersion state of 2D black phosphorus (BP) nanosheets is of great significance for the application of BP based materials. However, the dispersion state of BP colloids cannot be analyzed by the conventional methods based on the optical signal detecting due to the intensive light absorption of BP in the ultraviolet-visible region and the high turbidity caused by the aggregation of pristine BP nanosheets. In this work, 3D light scattering has been proven to be an effective technique to characterize the dispersion characteristics of nanocolloids with intensive light absorption and limited dispersity by suppressing multiple scattering. The effect of the concentration, the temperature and the solvent on the dispersion stability of BP nanosheets has been systematically studied by modulated 3D cross-correlation. It has been shown that measurements at smaller angles can obtain better autocorrelation functions. The BP colloids exhibit excellent colloidal stability when the concentration is below 250 μgmL−1, above which aggregation tends to form. Increasing the temperature has shown to result in the formation of aggregation in the colloids. BP nanosheets possess better dispersion state in polar solvents than in nonpolar solvents, and the aggregation process in nonpolar solvents can be monitored by the slow relaxation mode of 3D light scattering. This study indicates that 3D light scattering paves way to analyze the dispersion dynamics of various 2D nanoparticle colloids with intensive light absorption and poor dispensability.