Influence of particle shape on the rheological behavior of three-phase non-brownian suspensions

Capillary suspensions are three-phase fluids comprising a solid and two immiscible, liquid phases with unique texture and flow properties. So far, research focused on isometric particles, here we discuss how the addition of a second, immiscible fluid affects structure and flow of suspensions including anisotropic particles. Differently shaped calcium carbonate as well as graphite and aluminum particles have been investigated. For needle-shaped and scalenohedral particles no increase in yield stress sigma(y) or storage modulus G' characteristic for a strong capillary force controlled, percolating particle network is observed when a secondary fluid is added. In contrast, a pronounced increase in sigma(y) and G' is found when a secondary fluid is introduced to suspensions of plate-like particles and optical as well as electron microscopy confirm the formation of a sample-spanning network characteristic for capillary suspensions. Suspensions of isometric particles exhibit a distinct maximum in sigma(y) or G' at low fractions of secondary fluid to particle volume fraction phi(sec)/phi(solid) approximate to 0.1-0.2, whereas suspensions of plate-like particles exhibit constant sigma(y) and G' values over a wide range of phi(sec)/phi(solid) values up to approximate to 1 until spherical agglomeration occurs. Due to the different shape of the capillary bridges suspensions of plate-like particles can accommodate much larger fractions of secondary fluid until spherical agglomeration sets in than systems including spherical particles thus offering a versatile basic concept for the design of complex multi-component paste-like products. (C) 2016 Elsevier B.V. All rights reserved.