Effects of particle stiffness on the extensional rheology of model rod-like nanoparticle suspensions.

Christian Lang,Christian Clasen,M Paul Lettinga,Jan Hendricks,Naveen K Reddy,Jonathan P Rothstein,Zhenkun Zhang,Jan Vermant

doi:10.1039/c8sm01925h

Abstract

The linear and nonlinear rheological behavior of two rod-like particle suspensions as a function of concentration is studied using small amplitude oscillatory shear, steady shear and capillary breakup extensional rheometry. The rod-like suspensions are composed of fd virus and its mutant fdY21M, which are perfectly monodisperse, with a length on the order of 900 nm. The particles are semiflexible yet differ in their persistence length. The effect of stiffness on the rheological behavior in both, shear and extensional flow, is investigated experimentally. The linear viscoelastic shear data is compared in detail with theoretical predictions for worm-like chains. The extensional properties are compared to Batchelor's theory, generalized for the shear thinning nature of the suspensions. Theoretical predictions agree well with the measured complex moduli at low concentrations as well as the nonlinear shear and elongational viscosities at high flow rates. The results in this work provide guidelines for enhancing the elongational viscosity based on purely frictional effects in the absence of strong normal forces which are characteristic for high molecular weight polymers.

Highlights

3500 Hasselt, Belgium e IMO, IMOMEC, Hasselt University, Wetenschapspark 1, 3590 Diepenbeek, Belgium f Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA, 01003, USA g Department of Materials, ETH Zurich, 8093 Zurich, Switzerland † Electronic supplementary information (ESI) available: Intrinsic moduli of fd and fdY21M at all measured concentrations
Intrinsic viscosities from shear rheology at low Peclet numbers are successfully used in determining the length of carbon nanotubes using the Kirkwood–Batchelor theory,[25,26,27,28,29] which is in agreement with atomic force microscopy (AFM) results
We find Le E 0.3 mm for fd virus and Le E 0.9 mm for fdY21M, thereby, roughly confirming the difference in persistence length between the two systems

Summary

Introduction

The rheology of rod-like nanoparticle suspensions was reviewed by Solomon[7] who identified four physiochemical properties that control their behavior: interactions between particles, aspect ratio, persistence length, and number density. Most systematic studies have been carried out for rod-like nanoparticle suspensions with relatively low aspect ratios L/d o 20.22–24 many large aspect ratio rod-like particle suspensions, e.g. carbon nanotubes, glass fibers or actin, are typically polydisperse. The most extensively studied rod-like particles are carbon nanotubes and actin filaments, of which the material functions in shear and oscillatory flow have been determined. Intrinsic viscosities from shear rheology at low Peclet numbers are successfully used in determining the length of carbon nanotubes using the Kirkwood–Batchelor theory,[25,26,27,28,29] which is in agreement with atomic force microscopy (AFM) results.

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Conclusion