Paper Number
PO59 

Session
Poster Session

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

Presentation Date and Time
October 13, 2021 (Wednesday) 6:30

Track / Room
Poster Session / Ballroom 1-2-3-4

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; surfactants

Text of Abstract
Rheological modifiers are used to tune the rheology of products, including in products that change state during end-use. To effectively use rheological modifiers the material structure and rheological properties must be well understood. Hydrogenated castor oil (HCO) is currently used as a rheological modifier in home care products, but this rod is polydisperse, which could produce complex heterogeneous structures. To determine the effect of polydispersity on rheological modification, this work characterizes gelation of HCO and polyamide (PA), a monodisperse colloidal rod, using multiple particle tracking microrheology (MPT). In MPT, fluorescent probe particles are embedded in the sample and their Brownian motion is measured. Our system consists of a colloid (HCO or PA), a surfactant (linear alkylbenzene sulfonate, LAS), and a non-absorbing polymer (polyethylene oxide, PEO). PEO is used to drive gelation through depletion interactions. We measure these materials as depletion interactions are increased and gel the system. MPT data are analyzed using time-cure superposition to determine the critical values at the phase transition. We determine that the critical relaxation exponent is dependent on LAS:colloid, but PA and HCO have similar critical value. The critical relaxation exponent is lower for LAS:colloid=16, indicating a tightly associated network, than LAS:colloid>16, indicating a loosely associated network. This difference is due to a difference in the zeta potential between these two systems, which indicates that the strength of the electrostatic force changes when LAS:colloid is varied. This changes the starting material structure and leads to different gel evolution. This study shows that, for both systems, the rheology and microstructure during gelation depends on LAS:colloid, but 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.