Paper Number
SC39 

Session
Suspensions and Colloids

Title
Defining the structure and properties of colloidal rod systems during dynamic phase transitions

Presentation Date and Time
October 12, 2022 (Wednesday) 10:30

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

  1. He, Shiqin (Lehigh University, Chemical and Biomolecular Engineering)
  2. Pascucci, Dominic (Lehigh University, Chemical and Biomolecular Engineering)
  3. Caggioni, Marco (Procter & Gamble)
  4. Lindberg, Seth (The Procter & Gamble Co)
  5. Schultz, Kelly M. (Lehigh University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Shiqin He1, Dominic Pascucci1, Marco Caggioni2, Seth Lindberg2 and Kelly M. Schultz1
1Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, PA 18015; 2The Procter & Gamble Co, West Chester, OH 45069

Speaker / Presenter 
Schultz, Kelly M.

Keywords
experimental methods; colloids; consumer products; gels; surfactants

Text of Abstract
Rheological modifiers are added to formulations to tune rheology, enable function and drive phase changes requiring an understanding of material structure and properties. Of particular interest is how these modifiers change the rheology during phase transitions. We characterize the dynamic evolution of two colloidal rod systems using multiple particle tracking microrheology (MPT). MPT measures the Brownian motion of embedded probes to extract rheological properties. These systems include a colloid (monodisperse polyamide, PA or polydisperse hydrogenated castor oil, HCO), surfactant (linear alkylbenzene sulfonate, LAS) and non-absorbing polymer (polyethylene oxide, PEO) which drives gelation by depletion interactions. To determine the role of the starting material microstructure in gelation the ratio of LAS to colloid is varied and has two regimes: LAS:colloid=16 and LAS:colloid>16. We measure different material property evolution at different LAS:colloid. We analyze colloidal gelation using time-cure superposition to quantitatively determine the critical relaxation exponent, n, which depends on LAS:colloid. n is lower at LAS:colloid=16 than LAS:colloid>16 indicating that the system structure transitions from a tightly associated network to a loosely associated network at the phase transition. We hypothesize this is due to the microstructure of the starting material, which is verified by zeta potential measurements. At LAS:colloid=16, the colloids start as stable single colloids that form a sample-spanning gel network. At LAS:colloid>16, the colloidal rods start bundled and then those bundles form gel networks. We compare the results of PA and HCO, and find that they are similar during sol-gel transitions. This indicates that polydispersity does not affect the mechanism, rheology and structure of the material during a phase transition. This study will inform future product design by providing formulation guidance to reach desired rheological properties while minimizing trial-and-error experiments.