Paper Number
SG14 

Session
Self-assembled Systems, Gels and Liquid Crystals

Title
Adhesive hard rods: A thermoreversible model system to quantify the effects of particle shape anisotropy and short-range attractions on dynamic arrest transitions

Presentation Date and Time
February 13, 2017 (Monday) 5:15

Track / Room
Track 3 / White Ibis

Authors (Click on name to view author profile)

1. Murphy, Ryan P. (University of Delaware, Chemical and Biomolecular Engineering)
2. Wagner, Norman J. (University of Delaware, Chemical & Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Ryan P. Murphy and Norman J. Wagner
Chemical & Biomolecular Engineering, University of Delaware, Newark, DE 19716

Speaker / Presenter 
Wagner, Norman J.

Text of Abstract
Suspensions containing anisotropic colloids such as clays, proteins, and various organic and inorganic crystals are common in many particle-based technologies. Particle shape anisotropy is known to affect the thermodynamic and rheological properties of colloidal suspensions, for example, by influencing the random close packing, shear thinning or thickening behavior, liquid crystal phase behavior, and elasticity at low particle volume fractions. However, we lack a comprehensive understanding of how the coupled effects of particle shape anisotropy and interparticle attractions influence dynamic arrest transitions, or gel and glass formation. An experimental model system of adhesive hard rods (AHR) was developed to quantify these effects for rod-like systems with tunable aspect ratios and short-range, thermoreversible attractions. The AHR system is composed of octadecyl-coated silica rods suspended in tetradecane, serving as a chemically consistent, one-dimensional extension of the well-studied adhesive hard sphere system. Various experimental techniques characterized the dynamic arrest transitions of AHR suspensions as a function of the particle aspect ratio (3 to 7), a wide range of volume fractions (0.1 to 0.5), and moderate temperatures (15 to 40 C). SAOS measurements revealed thermoreversible transitions from fluid-like to gel-like states. Quasi-elastic light scattering methods probed the particle dynamics and further quantified the critical transition temperatures for dynamical arrest. Neutron and X-ray scattering methods also showed unique microstructural transitions between the fluid-like and gel-like states. Further quantification, simulation, and modeling of the AHR system will help link the coupled effects of particle shape and attraction strength with the macroscopic rheology. We propose that the tunable AHR system enables quantitative mapping of the gel, glass, and phase boundaries onto a universal state diagram for anisotropic colloids with short-range attractions.