Rheology of Concentrated Suspensions Containing Weakly Attractive Alumina Nanoparticles

Abstract

The use of nanoparticles for the fabrication of new functional ceramics and composites often requires the preparation of concentrated fluid suspensions. However, suspensions containing nanoparticles are limited in solids content because of the excluded volume formed by the dispersant adlayer around the particles. We investigated the effect of the adlayer thickness on the rheological behavior of suspensions containing model alumina nanoparticles, using dispersant molecules with deliberately tailored chain length. The apparent viscosity and yield stress of the particle suspensions were markedly decreased by increasing the dispersant length, mainly due to a reduction of the attractive forces among particles. Fluid suspensions with solids content up to 35 vol% were prepared in toluene using a dispersant length of 2.5 nm. Our experimental results and viscosity predictions based on a hard sphere model indicate that fluid suspensions with up to 43 vol% of 65 nm alumina particles could be prepared using an optimum dispersant length of about 3.6 nm.

Rheological behaviour of nanofluids

“…These controversies suggest that the properties of the base liquid and nanoparticles, and the interaction between the base liquid and nanoparticles play an important role in determining the rheological behaviour of nanofluids. It should be noted that the non-Newtonian behaviour observed by Ding et al (2006) for carbon nanotube nanofluids, Kwak and Kim (2005) for CuO nanorod nanofluids, Tseng and Lin (2003) for concentrated aqueous suspensions of TiO 2 , and Studart et al (2006) for Al 2 O 3 -MEK/T (methyl ethyl ketone/toluene) suspensions could be attributed, at least partially, to very different particle shape and concentration range. As this work focuses on spherical particles, particle shape effects will not be discussed further in this paper.…”

“…It is different from the results of aqueous suspensions of spherical TiO 2 nanoparticles (He et al 2007) and PG based Al 2 O 3 nanofluids (Prasher et al 2006), where linear correlations were obtained. For concentrated suspensions, the viscosity increase is shown to depend on nanoparticle volume concentration in an exponential manner; see for example Tseng and Lin (2003) for aqueous-based TiO 2 suspensions and Studart et al (2006) for MEK/T-based suspensions of Al 2 O 3 . The reasons for these differences are discussed in section 4.…”

“…There are discrepancies in the reported studies of nanofluids. Some concluded that nanofluids were Newtonian (Das et al 2003;Prasher et al 2006;Wang et al 1999;Xuan and Li 2000); others found non-Newtonian behaviour of nanofluids He et al 2007;Kwak and Kim 2005;Studart et al 2006;Tseng and Lin 2003). There is an urgent need to address this issue.…”

Yielding of weakly attractive nanoparticle networks

“…By selecting an anchoring group displaying high affinity to the particle surface and using solvent mixtures that favor an extended conformation of the alkyl chain towards the liquid medium, a densely packed steric layer of well-defined thickness (d) in the range of 0.97-1.90 nm is formed around the particles. Based on our earlier study, 29 toluene was used as the liquid medium of networks containing molecules with longer hydrocarbon chains (n $ 8), whereas a mixture of 35 wt% toluene and 65 wt% methyl ethyl ketone was taken as the liquid phase of networks containing shorter ligands (n ¼ 3 and 4). The effective volume fraction of particles, f eff , is calculated from the adlayer thickness, d, using the relation:…”

Heat transfer measurement in oil-based nanofluids.

“…Newtonian behaviors [17,18,24,76] while others have been determined to be non-Newtonian [21,49,77,78].…”