Paper Number
ET15 

Session
Advanced Experimental Techniques/Methods in Rheology

Title
Non-equilibrium micro-rheology of a model soft colloidal glass

Presentation Date and Time
October 17, 2018 (Wednesday) 10:15

Track / Room
Track 5 / San Felipe Room

Authors (Click on name to view author profile)

  1. Li, Qi (Texas Tech University, Chemical Engineering)
  2. Peng, Xiaoguang (University of Connecticut, Chemical & Biomolecular Engineering)
  3. McKenna, Gregory B. (Texas Tech University, Department of Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Qi Li1, Xiaoguang Peng2, and Gregory B. McKenna1
1Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409; 2Chemical & Biomolecular Engineering, University of Connecticut, Storrs, CT

Speaker / Presenter 
Li, Qi

Text of Abstract
Micro-rheology has proven to be a powerful tool in measuring viscoelastic properties for colloidal systems [1,2], and is known to capture the equilibrium dynamics in colloids approaching their concentration glass transition [3]. In this study, the diffusing wave spectroscopy (DWS)-based micro-rheology was used with different optical geometries (backscattering and transmission) as well as different sample thicknesses, which enable us to probe the system dynamics at different length scales [2]. The object is to explore more in non-equilibrium dynamics and address the range of utility of DWS as a micro-rheological method. A thermo-sensitive PS-PNIPAM/AA model colloidal system was investigated in equilibrium and non-equilibrium states by temperature-jump induced volume-fraction jump experiments. We find that in the case of the equilibrium state, the dynamics is insensitive to the optical geometry (backscattering and transmission) and length scales; whereas in the non-equilibrium state, significant differences in the measured dynamics is observed for the different geometries and length scales. The difference in non-equilibrium behaviors for different length scales provides a possibility to examine more closely the aging mechanism for colloidal glasses. Furthermore, the fact that length scale effects were observed only in non-equilibrium conditions indicates that, while dynamic heterogeneity is associated with the non-equilibrium dynamics of colloidal glasses, it does not seem to be the controlling factor for the colloidal glass transition process. [1] J. Liu, M. L. Gardel, K. Kroy, E. Frey, B. D. Hoffman, J. C. Crocker, A. R. Bausch, and D. A. Weitz. Phys. Rev. Lett. 96, 118104 (2006). [2] W. Brown. Dynamic Light Scattering: The Method and Some Applications. Oxford Univ. Press, Oxford. 1993 [3] Q. Li, X. Peng, and G. B. McKenna. Soft Matter 13, 1396 (2017).