Transcript Folie 1 - univie.ac.at

Non-Equilibrium Computer Experiments
of Soft Matter Systems
Arash Nikoubashman
Institute of Theoretical Physics
Vienna University of Technology
[email protected]
Table of Contents
• Introduction
• Simulation Technique
• Flow Properties of Cluster Crystals
• Cluster Crystals under Shear Flow
• Cluster Crystals under Poiseuille Flow
• Conclusions & Outlook
• Appendix
Introduction
What is Soft matter?
• Mesoscopic particles (1nm – 1mm) dispersed in an
atomic solvent
Introduction
What is Soft matter?
• Mesoscopic particles (1nm – 1mm) dispersed in an
atomic solvent
• Everyday soft materials:
• Blood
Introduction
What is Soft matter?
• Mesoscopic particles (1nm – 1mm) dispersed in an
atomic solvent
• Everyday soft materials:
• Blood
• Paint
Introduction
What is Soft matter?
• Mesoscopic particles (1nm – 1mm) dispersed in an
atomic solvent
• Everyday soft materials:
• Blood
• Paint
• Milk
Introduction
What is Soft matter?
• Mesoscopic particles (1nm – 1mm) dispersed in an
atomic solvent
• Everyday soft materials:
•
•
•
•
Blood
Paint
Milk
Ice Cream
Introduction
…and why are these substances soft?
• Elastic constant G for a simple cubic crystal1:
G = 1/v eF’’(r=a)
Atomic Crystal
Colloidal Crystal
e
10-1 – 10 eV
kBT ≃ 1/40 eV
F
Irrelevant
Irrelevant
v
Å3 = 10-30 m3
10-18 – 10-21 m3
Gcolloidal/Gatomic = 10-12 – 10-9
[1] C. N. Likos, Phys. Rep. 348, 267 (2001)
Introduction
Why is soft matter out of equilibrium interesting?
Introduction
It is omnipresent in our daily lives!
Introduction
It is omnipresent in our daily lives!
• Cellular transport2
[2] Medalia et al., Science 298, 1209 (2002)
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)
Introduction
It is omnipresent in our daily lives!
• Cellular transport
• DNA sequencing
• Blood flow4
[4] Pan et al., Microvasc. Res. 82, 163 (2011)
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)
Introduction
It is omnipresent in our daily lives!
• Cellular transport
• DNA sequencing
• Blood flow
• Microfluidics
• Paint
Introduction
It is omnipresent in our daily lives!
• Cellular transport
• DNA sequencing
• Blood flow
• Microfluidics
• Paint
• Oil recovery
Introduction
Interesting flow properties!
• Shear thickening6
[6] http://www.youtube.com/watch?v=KL8--cmew3k
Introduction
Interesting flow properties!
• Shear thickening
• Shear thinning7
[7] http://www.youtube.com/watch?v=pes1Ju1Cl8o
Introduction
Interesting flow properties!
• Shear thickening
• Shear thinning
• Ferrofluidics8
… and much more
[8] http://www.kodama.hc.uec.ac.jp/spiral/
Table of Contents
• Introduction
• Simulation Technique
• Flow Properties of Cluster Crystals
• Cluster Crystals under Shear Flow
• Cluster Crystals under Poiseuille Flow
• Conclusions & Outlook
• Appendix
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/
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)
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)
Simulation Technique
• Flow profile not superimposed, but self-emerging
(through the appropriate boundary conditions)
• Thus, we can induce:
• Wall-Slip
• Nonlinear velocity profiles
• …
Shear flow
Poiseuille flow
Table of Contents
• Introduction
• Simulation Technique
• Flow Properties of Cluster Crystals
• Cluster Crystals under Shear Flow
• Cluster Crystals under Poiseuille Flow
• Conclusions & Outlook
• Appendix
Flow Properties of Cluster Crystals
• We study particles interacting via GEM potential:
• Potential is:
• Purely repulsive
• Bounded
Partial and full particle
overlap is possible
Flow Properties of Cluster Crystals
GEM crystals have peculiar equilibrium properties
• Clustering
• Density independent lattice constant
• Activated hopping
Cluster Crystals under Shear Flow
hard
soft
• What happens out of equilibrium?
• Let’s shear the system11!
[11] A. Nikoubashman, G. Kahl and C. N. Likos, Phys Rev. Lett. 107, 068302 (2011)
Cluster Crystals under Shear Flow
Cluster Crystals under Shear Flow
hard
soft
• Shear destroys crystalline order
• System melts and array of strings emerges!
Cluster Crystals under Shear Flow
hard
soft
• What if we shear even stronger?
Cluster Crystals under Shear Flow
hard
soft
• Particles can escape from their string
• System destabilizes and melts completely
Cluster Crystals under Shear Flow
• Potential exerted by a string of GEM particles
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
Cluster Crystals under Shear Flow
• Free volume decreases rapidly
• Fluid resistance grows, viscosity increases
Shear-stress as a function of shear-rate
Table of Contents
• Introduction
• Simulation Technique
• Flow Properties of Cluster Crystals
• Cluster Crystals under Shear Flow
• Cluster Crystals under Poiseuille Flow
• Conclusions & Outlook
• Appendix
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)
Cluster Crystals under Poiseuille Flow
Scenario I
Scenario II
• String-formation close to
the walls
• Crystalline layer(s) at the
center of the channel
• 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
Cluster Crystals under Poiseuille Flow
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
Cluster Crystals under Poiseuille Flow
Flow quantization
Plateau height of the plug flow pattern
Width of the flat part of the velocity profile
Table of Contents
• Introduction
• Simulation Technique
• Flow Properties of Cluster Crystals
• Cluster Crystals under Shear Flow
• Cluster Crystals under Poiseuille Flow
• Conclusions & Outlook
• Appendix
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
The End
Thank you for your attention!
Table of Contents
• Introduction
• Simulation Technique
• Flow Properties of Cluster Crystals
• Cluster Crystals under Shear Flow
• Cluster Crystals under Poiseuille Flow
• Conclusions & Outlook
• Appendix
Appendix
Flow dynamics: two step process
1. Streaming step:
Appendix
Flow dynamics: two step process
1. Streaming step:
2. Collision step:
Appendix
• String-formation independent of initial configuration
• Can we exploit this to accelerate crystallization?
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)
Appendix
Appendix
Appendix