Colloid Rheology and Dynamics

The physics of soft matter is exemplified by the behavior of colloidal dispersions in that these discrete particle systems are frequently used as models for molecular systems, both crystalline and amorphous. In our laboratories we are exploring systematically the relationships between amorphous colloidal systems and molecular glasses through a novel set of experimental capabilities that permit us to make concentration-jump experiments analogous to the Kovacs’ type of experiment developed for studying the structural recovery of molecular glasses. The work is complemented by a collaboration with R. Zia at Stanford University whose group is performing large scale computational simulations of hard-sphere colloids subjected to similar conditions to those in our experiments. We have been measuring the dynamics of soft colloids that are thermosensitive, thus permitting temperature change to vary the particle size at constant number density, leading to concentration-jump conditions when the temperature is changed rapidly. Our findings show that the colloid-molecular glass paradigm is not straight-forward as the response of the colloidal glasses while being qualitatively similar to those of molecular glasses in the Kovacs’ type of experiment, they are quantitatively different. Our work is aimed at furthering the insights gained and to also examine how concentration-jumps relate to isochoric temperature-jumps in molecular glasses. Considerations of hard-sphere vs. soft sphere responses are also being examined.

Some Publications

1. X. Di, X. Peng and G.B. McKenna*, “Dynamics of a thermo-responsive microgel colloid near to the glass transition,” J. Chem. Phys. 140, 054903 (2014).

2. X. Peng and G.B. McKenna*, “Comparison of the Physical Aging Behavior of a Colloidal Glass after Shear-Melting and Concentration Jumps,” Physical Review E, 90, 050301 (2014).

3. X. Peng and G.B. McKenna*, “Physical Aging and Structural Recovery in a Colloidal Glass Subjected to Volume Fraction-Jump Conditions,” Physical Review E., 93, 042603 (2016).

4. Q. Li, X. Peng, and G.B. McKenna*, “Long-Term Aging Behaviors in a Model Soft Colloidal System,” Soft Matter, 13, 1396-1404 (2017).

5. S. Banik and G.B. McKenna*, “Isochoric structural recovery in molecular glasses and its analog in colloidal glasses,” Phys. Rev. E., 97, 062601 (2018).

6. X. Peng, J.G. Wang, Q. Li, D. Chen, R.N. Zia* and G.B. McKenna*, “Exploring the validity of time-concentration superposition in glassy colloids: Experiments and simulations,” Physical Review E, 98, 062602 (2018).

7. Q. Li, X. Peng and G.B. McKenna*, “Physical aging and compressed exponential behaviors in a model soft colloidal system,” Soft Matter, 15, 2336-2347 (2019).

8. Q. Li, X. Peng, D. Chen and G.B. McKenna*, “The Laplace approach in microrheology,” Soft Matter, 16, 3378-3383 (2020).

9. J. G. Wang, Q. Li, X. Peng, G. B. McKenna and R. N. Zia*, ““Dense diffusion” in colloidal glasses: short-ranged long-time self-diffusion as a mechanistic model for relaxation dynamics,” Soft Matter, 2020; DOI: 10.1039/D0SM00999G.

Funding

• National Science Foundation. Division of Chemical, Bioengineering, Environmental, and Transport Systems (CBET).
• John R. Bradford Endowment at Texas Tech University.
• Paul Whitfield Horn Professorship at Texas Tech University.