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Computer simulations of amphiphilic worms and bi-layers. Molecular dynamics simulations Coarse amphiphiles Worms Bi-layers [polymer melts]. W.J. Briels W.K. den Otter

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Molecular dynamics simulations Coarse amphiphiles Worms Bi-layers [polymer melts].

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Molecular dynamics simulations (N,V,U) i)Classical mechanics ii) Periodic boundary conditions iii) N,V,U

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Molecular dynamics simulations (N,V,T) i) Temperature ii) Thermostat Velocity scaling Langevin thermostat system Thermostat

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Molecular dynamics simulations Measure: Yes i)Energy, pressure ii)Averages (e.g. structural properties) iii)Free energy differences No Free energies, entropies, …

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Molecular dynamics simulations Coarse amphiphiles Worms Bi-layers [polymer melts].

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Simulation Models Bi-layer amphiphile Worm amphiphile Water R.Goetz and R.Lipowsky, J.Chem.Phys. 108, 7397 (1998)

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Molecular dynamics simulations Coarse amphiphiles Worms Bi-layers [polymer melts].

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Cylindrical micelle (worm) W.K. den Otter, S.A. Shkulipa and W.J. Briels, J. Chem. Phys. 119, 2363 (2003)

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Free energy i)Tension ii)Bending fluctuations

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Elastic modulus

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Bending fluctuations

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Simulating an entanglement

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Entangled worm Twisted PBC: M.P. Allen and A.J. Masters, Mol. Phys. 79, 277 (1993) 840 amphiphiles 45800 solvent

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Entanglement under tension WJB, P. Mulder and WKdO, J. Phys.: Condens. Matter. 16, S3965 (2004)

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Tension relaxation merging ‘chromosoming’

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Merging

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Relaxing

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backbone 270 amphiphiles; tail 90 amphphiles Eating

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Consequences Shear thickening near overlap concentration. Shear thinning at large shear-rates by aligning of worms in flow direction.

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Shear thinning str ess Shear rate Shear thinning by merging and alignment

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Shear banding of micellar worms

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Molecular dynamics simulations Coarse amphiphiles Worms Bi-layers [polymer melts].

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Amphiphilic bilayer (membrane) 1152 amphiphiles 16740 solvent

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Bi-layer free energy Helfrich

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Pore

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Punctured bi-layer free energy

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Stable states

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Radius versus stretch T.V. Tolpekina, WKdO and WJB, J. Chem. Phys. (Oct. 2004)

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Finite size scaling

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Radius versus stretch 1152 288

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Tension versus radius

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Molecular dynamics simulations Coarse amphiphiles Worms Bi-layers [polymer melts].

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Polymer melt C 120 H 242

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Equations of Motion Langevin equation

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Coarse model from atomistic simulation Friction Potential of mean force

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Entanglements

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Results-diffusion coefficients

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Results-viscosities

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Thank you !! Brrrrrrr

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