Paper Number
SM5 

Session
Polymers Solutions, Melts and Blends

Title
Brownian dynamics simulation of the gel transition of reversibly associating polymers

Presentation Date and Time
October 10, 2022 (Monday) 11:10

Track / Room
Track 2 / Sheraton 3

Authors (Click on name to view author profile)

  1. Robe, Dominic M. (Monash University, Chemical and Biological Engineering)
  2. Santra, Aritra (Monash University, Department of Chemical and Biological Engineering)
    Santra, Aritra (The City College of New York, CUNY, Levich Institute)
  3. McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)
  4. Prakash, J. Ravi (Monash University, Chemical and Biological Engineering)

Author and Affiliation Lines (in printed abstract book)
Dominic M. Robe1, Aritra Santra1,2, Gareth H. McKinley3 and J. Ravi Prakash1
1Chemical and Biological Engineering, Monash University, Melbourne, Victoria 3800, Australia; 2Levich Institute, The City College of New York, CUNY, New York, NY 10017; 3Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142

Speaker / Presenter 
Prakash, J. Ravi

Keywords
computational methods; gels; polymer solutions

Text of Abstract
We present simulations of physical gels near the gel transition using Brownian dynamics. The transition of a polymer solution from a fluid to a gel has been studied extensively for the case of permanent chemical crosslinks. Gels with thermoreversible physical crosslinks show great promise for designing materials with tuneable rheology and self-healing properties but have many unanswered questions. We present simulation predictions of dynamic moduli as functions of frequency and concentration. Due to the scale-free and semidilute character of critical gels, fully capturing their structure and dynamics requires inclusion of hydrodynamic interactions (HI), a large simulation volume, and time scales spanning several orders of magnitude. Jim Swans’ group recently developed an algorithm for the efficient computation of HI in colloids. We have adapted this algorithm for polymer chains, making the simulation of physical gels at the transition point using Brownian Dynamics tractable for the first time. We discuss the effect of the dissociation time on the typical critical gel behaviour. In particular, in a chemical gel, one expects the dynamic moduli to be parallel power law functions of frequency at the gel point. However, if the dissociation time is short, this power law may be cut off by the disintegration of the gel network after long times / low frequencies. We show that the typical signature of gelation can be recovered by increasing the effective strength of the associative interaction. Further, we show that the gel transition is still observable, even with weak associations, using several measurements, including the equilibrium stress autocorrelation, instantaneous shear modulus, and zero shear rate viscosity. We also show the structural emergence of a gel as a power law distribution of chain cluster sizes, indicating a divergence of the average cluster size. Finally, we compare the concentration dependence of these static and dynamic measurements of physical gels across the gel transition.