Anisotropic robustness of talc particles after surface modifications probed by atomic force microscopy force spectroscopy

As a versatile mineral, the crystalline hydrated magnesium silicate talcum, or talc, has been widely used in numerous industries from pharmaceutical formulations to composite material designs. Its efficient application as filler/additives incorporates the improvement in concomitant properties within materials, e.g., strength, which involves interactions between talc particles and aqueous/nonaqueous matrices. Successful property enhancement imposes ideal mixing and homogenous adhesion within a talc particle, but they are limited by the coexistence of face and edge surfaces of talc, which exhibit different level of hydrophobicity. Here, using atomic force microscopy force spectroscopy, we showed that although hydrophilic talc particles obtained from acid treatment or aminosilanization better adhered with materials representing a matrix, the anisotropic characters of the two surface types persisted. Conversely, the degree of talc's surface anisotropy reduced with the surface hydrophobization by aliphatic methylsilanization, but followed by the decrease in adhesion. With ten-fold difference in Hamaker constants of the probe/talc surface interacting pairs, we showed that the adhesions resulted from van der Waals interactions that suggested the influence of surface polarity. The insight from this work would provide grounds for strategies to modulate talc's adhesion, hydrophobicity and surface uniformity. (c) 2021 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.