(298e) Quantitative Analysis of Synthetic Platelet Exfoliation in Water and Platelet Aspect Ratio Distribution

We use atomic force microscopy (AFM) and dynamic light scattering (DLS) for quantitative analysis of exfoliation and aspect ratio distribution of suspended, exfoliated inorganic platelet materials in water, including natural Na+-montmorillonite (MMT) clay as well as synthetic calcium niobate perovskite (KCa₂Nb₃O₁₀). Tapping-mode AFM with appropriate image analysis allows us to unambiguously identify exfoliated platelets and to quantify the distributions of platelet thickness and aspect ratio. MMT disperses in water (as is well known) but only partially exfoliates. We use dry weight analysis, DLS, and AFM to assess the impact of sample preparation procedures for maximizing exfoliation and obtaining high quality AFM images. Unexfoliated MMT and other contaminant particles can be removed by low speed centrifugation, but large exfoliated platelets are increasingly removed as centrifugal acceleration increases. Dilution of MMT suspensions with acetone prior to deposition onto mica leads to high quality AFM images with many isolated platelets. Quantitative analysis shows that the distribution of MMT platelet thickness is narrow and centered near 1.0 nm, and that the platelet aspect ratio distribution is log-normal, which has not been previously reported. We find that the average aspect ratio measured by AFM correlates linearly with the effective spherical particle diameter measured by DLS. The perovskite does not exfoliate in water despite having a higher cation exchange capacity, but cation exchange with tetrabutyl ammonium does promote exfoliation. DLS and AFM results help us optimize perovskite solution preparation and show that the perovskite's aspect ratio also has a log-normal distribution.