Two-dimensional nanomaterials have garnered interest in recent years for their interesting properties. For example, such materials have a wide range of mechanical, thermal, and electronic properties that can lead us to improve conventional energy storage, protective films, electronics, and more. However, these applications have not been implemented by manufacturers, in part due to a lacking of fundamental knowledge about these materials, including the diffusion behavior in solution. In our research, we aim to visualize the diffusion motions of hexagonal boron nitride (h-BN). We use h-BN as a model of disk shape nanomaterial and predict the results will be applicable to other nanosheet materials. To analyze the diffusion, we first addressed the visualization of h-BN, since it is transparent under visible light and its fluorescence spectrum is out of the range of standard fluorescent microscopes. We addressed this by staining h-BN with a rhodamine B surfactant with a 12 carbon chain (Rh12). This surfactant was chosen for its fluorescence properties and its high binding affinity to h-BN in solution. In addition, hBN stained with fluorescent surfactants can be visualized using a standard fluorescence microscope. The dispersion and exfoliation efficiency of the sample for tracking was investigated by atomic force microscopy (AFM). The results indicate a good exfoliation and dispersion of the h-BN with our sample preparation method. We observed the translational diffusion of ~1.5-40 µm2 h-BN under three different sizes of confinement and determined their diffusion coefficients (Dt). The data suggested Dt decreased with larger area and smaller gap size as expected. However, interestingly, the data produced a single trend when they were normalized using their gap sizes, which demonstrates that the dependence with gap size is linear. We expect this study will provide important information about two-dimensional nanomaterials and help to improve our ability to make macroscopic materials using liquid-phase processing.

Visualization of hexagonal-boron nitride nanosheets with Rhodamine B surfactant for diffusion analysis

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.