Paper Number
SC37 

Session
Suspensions and Colloids

Title
Brownian dynamics simulations of colloids bridged by telechelic polymers under shear

Presentation Date and Time
October 12, 2022 (Wednesday) 9:50

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

1. Mani, Ethayaraja (Indian Institute of Technology Madras, Department of Chemical Engineering)
2. Parthasarathy, Gopal (University of Michigan, Department of Chemical Engineering)
3. Krishnamurthy, Sriram (Institute of Technology Madras, Department of Chemical Engineering)
4. Larson, Ronald (University of Michigan-Ann Arbor, Chemical Engineering Department)

Author and Affiliation Lines (in printed abstract book)
Ethayaraja Mani¹, Gopal Parthasarathy², Sriram Krishnamurthy¹ and Ronald Larson^2
1Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu 600036, India; ²Chemical Engineering Department, University of Michigan-Ann Arbor, Ann Arbor, MI 48105

Speaker / Presenter 
Larson, Ronald

Keywords
computational methods; colloids; polymer solutions; suspensions

Text of Abstract
We carry out the coarse-grained Brownian dynamics simulations of shearing flow of a colloidal suspension bridged by telechelic polymers with “sticky” end groups by treating the polymer as either a finitely extensible dumbbell or a three-bead “trumbbell,” and vary polymer concentration, and sticker strength epsilon over a range from 4 to 12 kT. The dynamics are the result of an interplay of the shear rate and three different times scales: the time tB for a sticker to be released from a particle surface, which is exponential in epsilon/kT, the time for the polymer chain to relax, tR, and the time for a colloid to diffuse a distance comparable to its own radius, tD. The zero-shear viscosity is estimated from equilibrium stress fluctuations, using the Green-Kubo formula, and found, as expected, to increase strongly with epsilon/kT, although also evidently influenced by tB. At shear rates corresponding to particle Peclet numbers above unity, mild shear-thinning is found, with shear-thinning exponent of -0.2 or less, much milder than seen in HEUR solutions in the absence of colloids, and with positive first normal stress difference, consistent with experimental data. The weakness of the shear thinning is likely due to the observed insensitivity of the loop-to-bridge and bridge-to-loop transition times to the imposed shear rate. These transition times are found to be proportional to the exponential of the attraction strength as expected. This study provides the first mesoscale simulations of these suspensions, useful for assessing and improving constitutive equations for these suspensions.