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Non-Equilibrium Computer Experiments of Soft Matter Systems Arash Nikoubashman Institute of Theoretical Physics Vienna University of Technology

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Presentation on theme: "Non-Equilibrium Computer Experiments of Soft Matter Systems Arash Nikoubashman Institute of Theoretical Physics Vienna University of Technology"— Presentation transcript:

1 Non-Equilibrium Computer Experiments of Soft Matter Systems Arash Nikoubashman Institute of Theoretical Physics Vienna University of Technology

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 – 1 m) dispersed in an atomic solvent

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

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

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

7 Introduction What is Soft matter? Mesoscopic particles (1nm – 1 m) 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 crystal 1 : G = 1/v (r=a) [1] C. N. Likos, Phys. Rep. 348, 267 (2001) Atomic CrystalColloidal Crystal – 10 eV k B T 1/40 eV Irrelevant vÅ 3 = m – m 3 G colloidal /G atomic = – 10 -9

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 transport 2 [2] Medalia et al., Science 298, 1209 (2002)

12 Introduction It is omnipresent in our daily lives! Cellular transport DNA sequencing 3 [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 flow 4 [4] Pan et al., Microvasc. Res. 82, 163 (2011)

14 Introduction It is omnipresent in our daily lives! Cellular transport DNA sequencing Blood flow Microfluidics 5 [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 thickening 6 [6]

18 Introduction Interesting flow properties! Shear thickening Shear thinning 7 [7]

19 Introduction Interesting flow properties! Shear thickening Shear thinning Ferrofluidics 8 [8] … and much more

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 account 9 [9]

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 ( N 2 )

23 Simulation Technique Our approach: Multi-Particle Collision Dynamics 10 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 Shear flow Poiseuille flow Simulation Technique Flow profile not superimposed, but self-emerging (through the appropriate boundary conditions) Thus, we can induce: Wall-Slip Nonlinear velocity profiles …

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? Lets shear the system 11 ! soft hard [11] A. Nikoubashman, G. Kahl and C. N. Likos, Phys Rev. Lett. 107, (2011)

29 Cluster Crystals under Shear Flow

30 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 flow 12 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: /c1sm06899g (2012)

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

39 Cluster Crystals under Poiseuille Flow

40 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 patternWidth 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 Thank you for your attention! The End

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 Flow dynamics: two step process 1.Streaming step:

47 Appendix Flow dynamics: two step process 1.Streaming step: 2.Collision step:

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

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

50 Appendix

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