The anisotropic characteristics of natural fibrous sepiolite as revealed by contact angle, surface free energy, AFM and molecular dynamics simulation

In this study, the anisotropic character of natural sepiolite was revealed by a combination of techniques involving contact angle measurements, Atomic Force Microscopy (AFM), and molecular dynamics (MD) simulations. Capillary rise technique was used to determine the change in contact angle values for several wetting liquids and calculate the surface free energy and acid/base components of sepiolite. The surface heterogeneity of sepiolite for a single fiber surface corresponding to roughness parameters was calculated from the AFM images. Finally, the interactions between water molecules and sepiolite mineral surfaces were also computationally analyzed using MD simulation to understand the interfacial water structure and the configuration of water molecules at the basal surface of sepiolite. It was found that due to the absence of hydrogen bonding sites, the hydrophobic sepiolite basal plane is not in close contact with water molecules, thus leaving a 3 angstrom void space at the basal plane. (c) 2012 Elsevier B.V. All rights reserved.