Non-Equilibrium Computer Experiments of Soft Matter Systems

1. Non-Equilibrium Computer Experiments of Soft Matter Systems ArashNikoubashman Institute of Theoretical Physics Vienna University of Technology arash.nikoubashman@tuwien.ac.at

2. Table of Contents • Introduction • Simulation Technique • Flow Properties of Cluster Crystals • Cluster Crystals under Shear Flow • Cluster Crystals under Poiseuille Flow • Conclusions & Outlook • Appendix

3. Introduction What is Soft matter? • Mesoscopic particles (1nm – 1mm) dispersed in an atomic solvent

4. Introduction What is Soft matter? • Mesoscopic particles (1nm – 1mm) dispersed in an atomic solvent • Everyday soft materials: • Blood

5. Introduction What is Soft matter? • Mesoscopic particles (1nm – 1mm) dispersed in an atomic solvent • Everyday soft materials: • Blood • Paint

6. Introduction What is Soft matter? • Mesoscopic particles (1nm – 1mm) dispersed in an atomic solvent • Everyday soft materials: • Blood • Paint • Milk

7. Introduction What is Soft matter? • Mesoscopic particles (1nm – 1mm) dispersed in an atomic solvent • Everyday soft materials: • Blood • Paint • Milk • Ice Cream

8. Introduction …and why are these substances soft? • Elastic constant G for a simple cubic crystal1: G = 1/veF’’(r=a) Gcolloidal/Gatomic = 10-12 – 10-9 [1] C. N. Likos, Phys. Rep. 348, 267 (2001)

9. Introduction Why is soft matter out of equilibrium interesting?

10. Introduction It is omnipresent in our daily lives!

11. Introduction It is omnipresent in our daily lives! • Cellular transport2 [2] Medaliaet al., Science 298, 1209 (2002)

12. Introduction It is omnipresent in our daily lives! • Cellular transport • DNA sequencing3 [3] M. Zwolak and M. Di Ventra, Rev. Mod. Phys. 80, 141 (2008)

13. Introduction It is omnipresent in our daily lives! • Cellular transport • DNA sequencing • Blood flow4 [4] Pan et al., Microvasc. Res. 82, 163 (2011)

14. Introduction It is omnipresent in our daily lives! • Cellular transport • DNA sequencing • Blood flow • Microfluidics5 [5] T. M. Squires and S. R. Quake, Rev. Mod. Phys. 77, 977 (2005)

15. Introduction It is omnipresent in our daily lives! • Cellular transport • DNA sequencing • Blood flow • Microfluidics • Paint

16. Introduction It is omnipresent in our daily lives! • Cellular transport • DNA sequencing • Blood flow • Microfluidics • Paint • Oil recovery

17. Introduction Interesting flow properties! • Shear thickening6 [6] http://www.youtube.com/watch?v=KL8--cmew3k

18. Introduction Interesting flow properties! • Shear thickening • Shear thinning7 [7] http://www.youtube.com/watch?v=pes1Ju1Cl8o

19. Introduction Interesting flow properties! • Shear thickening • Shear thinning • Ferrofluidics8 … and much more [8] http://www.kodama.hc.uec.ac.jp/spiral/

20. Table of Contents • Introduction • Simulation Technique • Flow Properties of Cluster Crystals • Cluster Crystals under Shear Flow • Cluster Crystals under Poiseuille Flow • Conclusions & Outlook • Appendix

21. Simulation Technique Computational task • Simulation of complex fluids in and out of equilibrium • Take hydrodynamic interactions (HI) of solvent into account9 [9] http://iffwww.kfa-juelich.de/www/Applets/iMPC/

22. Simulation Technique “Naïve” approach: pure MD simulations • Pro: • Straight-forward implementation • Atomistic simulations • Contra: • Large disparity in length- and timescales between solute and solvent particles Computationally expensive, O(N2)

23. Simulation Technique “Our” approach: Multi-Particle Collision Dynamics10 • Pro: • Hydrodynamics fully resolved • Thermal fluctuations preserved • Many different flow fields possible • Can be easily integrated into existing MD codes • Very fast and scalable algorithm, O(N) • Contra: • Coarse grained fluid [10] A. Malevanets & R. Kapral, J. Chem. Phys. 110, 8605 (1999)

24. Simulation Technique • Flow profile not superimposed, but self-emerging (through the appropriate boundary conditions) • Thus, we can induce: • Wall-Slip • Nonlinear velocity profiles • … Poiseuille flow Shear flow

25. Table of Contents • Introduction • Simulation Technique • Flow Properties of Cluster Crystals • Cluster Crystals under Shear Flow • Cluster Crystals under Poiseuille Flow • Conclusions & Outlook • Appendix

26. Flow Properties of Cluster Crystals • We study particles interacting via GEM potential: • Potential is: • Purely repulsive • Bounded Partial and full particle overlap is possible

27. Flow Properties of Cluster Crystals GEM crystals have peculiar equilibrium properties • Clustering • Density independent lattice constant • Activated hopping

28. Cluster Crystals under Shear Flow • What happens out of equilibrium? • Let’s shear the system11! ? soft hard [11] A. Nikoubashman, G. Kahl and C. N. Likos, Phys Rev. Lett. 107, 068302 (2011)

29. Cluster Crystals under Shear Flow

30. Cluster Crystals under Shear Flow • Shear destroys crystalline order • System melts and array of strings emerges! soft hard

31. Cluster Crystals under Shear Flow • What if we shear even stronger? ? soft hard

32. Cluster Crystals under Shear Flow • Particles can escape from their string • System destabilizes and melts completely soft hard

33. Cluster Crystals under Shear Flow • Potential exerted by a string of GEM particles

34. Cluster Crystals under Shear Flow • Free volume decreases rapidly • Fluid resistance grows, viscosity increases Free volume of the system as a function of shear-rate

35. Cluster Crystals under Shear Flow • Free volume decreases rapidly • Fluid resistance grows, viscosity increases Shear-stress as a function of shear-rate

36. Table of Contents • Introduction • Simulation Technique • Flow Properties of Cluster Crystals • Cluster Crystals under Shear Flow • Cluster Crystals under Poiseuille Flow • Conclusions & Outlook • Appendix

37. Cluster Crystals under Poiseuille Flow Expose cluster crystal to Poiseuille flow12 • Velocity profile of pure solvent: • Local shear rate: How does the crystal react? [12] A. Nikoubashman, G. Kahl and C. N. Likos, Soft Matter, DOI:10.10139/c1sm06899g (2012)

38. Cluster Crystals under Poiseuille Flow Scenario I Scenario II String phase is global, no microphase separation! • String-formation close to the walls • Crystalline layer(s) at the center of the channel Thick crystalline slab flows Crystalline layers act on strings as external potential Presence of crystal flattens velocity profile Strings break up into clumps

39. Cluster Crystals under Poiseuille Flow

40. Cluster Crystals under Poiseuille Flow Flow strongly affected by GEM crystal Velocity profile of the liquid in the presence of the GEM crystal Particle flux of solute particles. Arrows indicate when the first layer melts

41. Cluster Crystals under Poiseuille Flow Flow quantization Plateau height of the plug flow pattern Width of the flat part of the velocity profile

42. Table of Contents • Introduction • Simulation Technique • Flow Properties of Cluster Crystals • Cluster Crystals under Shear Flow • Cluster Crystals under Poiseuille Flow • Conclusions & Outlook • Appendix

43. Conclusions & Outlook Conclusions • Soft matter in and out of equilibrium is ubiquitous in our daily lives • MPCD technique is a suitable means for studying it Outlook • Monomer resolved simulations of cluster crystals • Polymeric networks under flow

44. The End Thank you for your attention!

45. Table of Contents • Introduction • Simulation Technique • Flow Properties of Cluster Crystals • Cluster Crystals under Shear Flow • Cluster Crystals under Poiseuille Flow • Conclusions & Outlook • Appendix

46. Appendix Flow dynamics: two step process • Streaming step:

47. Appendix Flow dynamics: two step process • Streaming step: • Collision step:

48. Appendix • String-formation independent of initial configuration • Can we exploit this to accelerate crystallization?

49. Appendix Yes, shear facilitates the crystallization process10! Color coded density profiles. Top half: unsheared system, lower half: presheared system [10] A. Nikoubashman, G. Kahl and C. N. Likos, Soft Matter, DOI:10.10139/c1sm06899g (2012)

50. Appendix