Paper Number
GN2                         My Program 

Session
Self-assemblies, Gels and Networks

Title
Microstructure & rheology of thermoreversible colloidal gels by 4D-RheoSANS

Presentation Date and Time
October 20, 2025 (Monday) 10:10

Track / Room
Track 2 / Sweeney Ballroom B

Authors (Click on name to view author profile)

  1. Wagner, Norman (University of Delaware)
  2. Egnaczyk, Ted (University of Delaware, Department of Chemical and Biomolecular Engineering)
  3. Hartt, Quent (University of Delaware)
  4. Kabra, Mukund (University of Delaware)
  5. Suman, Khushboo (IIT Madras)
  6. Neal, Christopher (ORNL)

Author and Affiliation Lines (in printed abstract book)
Norman Wagner1, Ted Egnaczyk1, Quent Hartt1, Mukund Kabra1, Khushboo Suman2 and Christopher Neal3
1University of Delaware, Newark, DE; 2IIT Madras, Chennai, India; 3ORNL, Oak Ridge, TN

Speaker / Presenter 
Wagner, Norman

Keywords
experimental methods; colloids; gels; suspensions

Text of Abstract
Fundamental questions concerning the interplay between particle interactions, dynamical arrest and phase behavior are addressed by rheology and neutron scattering measurements on a model, thermoreversible, colloidal adhesive hard sphere (AHS) suspension. In contrast to monotonic aging observed for shallow quenches, deeper quenching leads to an anomalous rheological behavior in the form of a reproducible drop in shear modulus, which has been attributed to arrested phase separation. To provide a mechanistic understanding, a new instrument for time-resolved small angle neutron scattering measurements under rheological shear flow (4D-RheoSANS) is deployed on multiple neutron beamlines to interrogate the microstructure on the nano-to-micro-scale. Upon sudden reduction in temperature from a liquid state to gel state, shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified in terms of alignment factor. Upon increasing the extent of thermal quench, the increased strength of interparticle attraction increases the viscosity as well as the degree of shear-induced anisotropy. SANS measurements as a function of time during various thermal quench are characterized in terms of an effective interaction strength and a Mason number. In this manner, the interplay of gelation, phase separation, and glass formation is explored where steady shear and large amplitude oscillatory shear (LAOS) provide a means to explore the nonequilibrium nature of these transitions as well as the effects of shear rejuvenation. This behavior is characterized by Structure Lissajous plots connecting time-dependent gel structure and rheology. Industrial relevance in understanding how shear affects the flow behavior of colloidal gels is demonstrated by application of the learnings from this study to improve the processing of commercial materials, such as geopolymers for construction materials, will be presented.