Paper Number
GN8                         My Program 

Session
Self-assemblies, Gels and Networks

Title
Investigating rough particle contact mechanics using optical tweezers

Presentation Date and Time
October 20, 2025 (Monday) 1:50

Track / Room
Track 2 / Sweeney Ballroom B

Authors (Click on name to view author profile)

  1. Pitell, Matthew A. (University of Delaware, Chemical and Biomolecular Engineering)
  2. Woolley, Lukas (ETH Zurich, Department of Materials)
  3. Vermant, Jan (ETH Zurich, Department of Materials)
  4. Furst, Eric M. (University of Delaware, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Matthew A. Pitell1, Lukas Woolley2, Jan Vermant2 and Eric M. Furst1
1Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716; 2Department of Materials, ETH Zurich, Zurich, Switzerland

Speaker / Presenter 
Pitell, Matthew A.

Keywords
colloids; gels

Text of Abstract
Colloidal gels are widespread. They are found in natural materials like muds to consumer products like toothpaste. Gels are made of networks of particles in contact. These contacts ultimately govern the material’s rheology. The elasticity and yielding of a colloidal gel can be related to the bending mechanics of a linear aggregate of particles by a micromechanical, three-point bending test [1]. This test gives us two key quantities: a single bond elasticity and a critical bending moment, which correlate to the storage modulus and yield stress of the bulk material. Particle contacts fail by a rolling frictional mechanism characterized by the depinning and rotation of particles [2]. While these experiments were conducted on model spherical particles, real world colloidal materials are often composed of particles with rough surfaces, which significantly alters the contact mechanics. Recent simulations have shown that the rotational friction between particles dictates and form the elastoviscous plasticity of colloidal gels [3]. As the rotational friction coefficient increases, the yield stress also increased. Roughness impedes the rolling of these particles resulting in an increase in the rotational friction barrier. Thus, the critical bending moment and yield stress increase as a function of the surface roughness. This work aims to experimentally validate the simulations by increasing the root-mean-squared (RMS) roughness of raspberry silica particles. Microscopic optical tweezer measurements combined with bulk rheology measurements elucidate the relationship between surface roughness and both microscopic interactions and bulk properties. [1] Pantina, J. P.; Furst, E. M. Phys. Rev. Lett. 2005, 94 (13), 138301. [2] Bonacci, F. et al. Phys. Rev. Lett. 2022, 128 (1), 018003. [3] More, R.; Mckinley, G. arXiv March 21, 2025.