1. 1 Supercooled liquids Zhigang Suo Harvard University Prager Medal Symposium in honor of Bob McMeeking SES Conference, Purdue University, 1 October 2014

2. Mechanics of supercooled liquids Journal of Applied Mechanics 81, 111007 (2014) 2 Jianguo Li Qihan Liu Laurence Brassart

3. Supercooled liquid 3 liquid supercooled liquid crystal Temperature Volume melting point

4. A simple picture of liquid A single rate-limiting step: molecules change neighbors Two types of experiments: viscous flow and self-diffusion 4

5. Stokes-Einstein relation Stokes (1851) Einstein (1905) 5 liquid particle

6. Success and failure of Stokes-Einstein relation TNB OTP IMC 6 Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014). Based on experimental data in the literature

7. A supercooled liquid forms a dynamic structure Ediger, Annual Review of Physical Chemistry 51, 99 (2000). The dynamic structure jams viscous flow, but not self-diffusion. 7

8. Given that the Stokes-Einstein relation fails, we regard viscous flow and self-diffusion as independent processes, and formulate a “new” fluid mechanics. Our paper Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

9. Homogeneous state Incompressible molecules Helmholtz free energy of a composite system Liquid force reservoir 9 Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

10. Thermodynamic equilibrium 10 membrane reservoir liquid osmosis Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

11. Linear, isotropic, viscous, “porous” liquid 11 Alternative way to write the model Analogous to Biot’s poroelasticity. (Poroviscosity?) Different from Newton’s law of viscosity change shape change volume Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

12. Inhomogeneous field Diffusion flux Net flux Convection flux 12 Suo. Journal of Applied Mechanics 71, 77 (2004)

13. 4 partial differential equations 13 4 boundary conditions Boundary-value problem Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

14. Length scale 14 Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

15. Time scale Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

16. 16 A cavity in a supercooled liquid A small object evolves by self-diffusion. A large object evolves by viscous flow. Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)

17. Summary 1.A supercooled liquid is partially jammed. A drop in temperature jams viscous flow, but does not retard self- diffusion as much. 2.We regard viscous flow and self-diffusion as independent processes, and formulate a “new” fluid mechanics. 3.A characteristic length exists. A small object evolves by self-diffusion, and a large object evolves by viscous flow. 4.Other partially jammed systems: cells, gels, glasses, batteries. 17 Li, Liu, Brassart, Suo. Journal of Applied Mechanics 81, 111007 (2014)