Paper Number
SC4 

Session
Suspensions, Colloids, and Granular Materials

Title
Rheological properties of phase transitions in polydisperse and monodisperse colloidal rod systems

Presentation Date and Time
October 11, 2021 (Monday) 11:05

Track / Room
Track 5 / Ballroom 6

Authors (Click on name to view author profile)

  1. He, Shiqin (Lehigh University, Chemical and Biomolecular Engineering)
  2. Pascucci, Dominic R. (Lehigh University, Chemical and Biomolecular Engineering)
  3. Caggioni, Marco (Procter & Gamble Company, Complex Fluid Microstructures)
  4. Lindberg, Seth (Procter & Gamble, Process and Engineering Development)
  5. Schultz, Kelly M. (Lehigh University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Shiqin He1, Dominic R. Pascucci1, Marco Caggioni2, Seth Lindberg3 and Kelly M. Schultz1
1Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA 18015; 2Complex Fluid Microstructures, Procter & Gamble Company, West Chester, OH 45069; 3Process and Engineering Development, Procter & Gamble, West Chester, OH 45069

Speaker / Presenter 
He, Shiqin

Keywords
colloids; gels; granular materials; surfactants

Text of Abstract
During manufacturing processes and product end-use, rheological modifiers can induce phase transitions. To design materials that undergo phase transitions, understanding the dynamic changes in rheology and microstructure is crucial. Colloidal rods are desirable rheological modifiers because they can tune rheology with small amounts of material. In this study, we characterize the rheological properties and microstructural changes of two colloidal rod systems used as rheological modifiers, polydisperse polyamide (PA) and monodisperse hydrogenated castor oil (HCO), during their phase transitions using multiple particle tracking microrheology (MPT). In MPT, Brownian motion of probes embedded in a sample is measured and related to rheological properties. Our systems consist of a colloid (PA or HCO), a surfactant (linear alkylbenzene sulfonate, LAS), and a non-absorbing polymer (polyethylene oxide, PEO) used to induce depletion interaction to drive gelation. Samples are characterized at different LAS:colloid. Measurement of probe diffusivity indicates that there is a change in microstructure when LAS:colloid is varied. Time-cure superposition (TCS) is then used to determine the critical values at different LAS:colloid. The critical relaxation exponent, n, is a measure of the material structure at the phase transition and is also dependent on LAS:colloid. n is higher for LAS:colloid>16, indicating loosely associated networks, than LAS:colloid=16, which indicates tightly associated networks. This is because the strength of the electrostatic force changes when LAS:colloid is varied. This changes the starting material structure and leads to different gel evolution. Our characterization determines that the rheology and microstructure at the phase transition of both systems depend on LAS:colloid. In addition, monodispersity and polydispersity does not affect gelation evolution. This work will inform future product design by providing guidance to specify desired rheology and minimize trial-and-error experiments.