Probing Anisotropic Surface Properties and Interaction Forces of Chrysotile Rods by Atomic Force Microscopy and Rheology

Abstract

Understanding the surface properties and interactions of nonspherical particles is of both fundamental and practical importance in the rheology of complex fluids in various engineering applications. In this work, natural chrysotile, a phyllosilicate composed of 1:1 stacked silica and brucite layers which coil into cylindrical structure, was chosen as a model rod-shaped particle. The interactions of chrysotile brucite-like basal or bilayered edge planes and a silicon nitride tip were measured using an atomic force microscope (AFM). The force-distance profiles were fitted using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which demonstrates anisotropic and pH-dependent surface charge properties of brucite-like basal plane and bilayered edge surface. The points of zero charge (PZC) of the basal and edge planes were estimated to be around pH 10-11 and 6-7, respectively. Rheology measurements of 7 vol % chrysotile (with an aspect ratio of 14.5) in 10 mM NaCl solution showed pH-dependent yield stress with a local maximum around pH 7-9, which falls between the two PZC values of the edge and basal planes of the rod particles. On the basis of the surface potentials of the edge and basal planes obtained from AFM measurements, theoretical analysis of the surface interactions of edge-edge, basal-edge, and basal-basal planes of the chrysotile rods suggests the yield stress maximum observed could be mainly attributed to the basal-edge attractions. Our results indicate that the anisotropic surface properties (e.g., charges) of chrysotile rods play an important role in the particle-particle interaction and rheological behavior, which also provides insight into the basic understanding of the colloidal interactions and rheology of nonspherical particles.

Aggregation of Elongated Colloids in Water

“…13,14 For example, asbestos particles—contaminants whose aspect ratios (length/diameter) range from 2 to 100—typically reside in soil that is at least partially saturated, and the aggregates formed in the aqueous phase may influence the mobility of particles in the environment. 15 The elongated particles exhibit anisotropic diffusion, 16 and their shape may also affect the spatial distribution of charges on the particle surface. 17 These factors may significantly influence the strength and direction of monomer attachment, whereas additional geometric effects 18 likely play a role in the structure of aggregates.…”

Surface-Charge Anisotropy of Scheelite Crystals

“…Surface charge anisotropy was studied for several oxide and silicate minerals in recent years including geothite 22 , alumina sapphire 23,24 , rutile 25 , muscovite 26 , talc 26, 27 , chlorite 16 and chrysotile 28 . The surface potential that is orientation dependent was also reported for fluorite 29 .…”

Effects of hydrothermal dewatering of lignite on rheology of coal water slurry

“…The higher slurry viscosity at a lower shear rate after HTD is probably due to the attractive particulate network induced by surface attractive forces among the particles, as HTD treated lignite particles carry less negative surface charge and exhibit higher contact angle (i.e. more hydrophobic) . At a higher shear rate (> 5 s −1 ), the viscosity of the coal water slurry made with lignite samples after the HTD process is lower than that of raw lignite water slurry.…”