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Kyongok Kang (FZ-Juelich)

From David pine’s webpage. Jan Dhont ICS-3. A (short) introduction to colloids Electric-field induced phase transitions, dynamical states and non-equilibrium critical behaviour in concentrated suspensions of rods. Kyongok Kang (FZ-Juelich). Introduction to Colloids.

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Kyongok Kang (FZ-Juelich)

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  1. From David pine’s webpage Jan Dhont ICS-3 A (short) introduction to colloids Electric-field induced phase transitions, dynamical states and non-equilibrium critical behaviour in concentrated suspensions of rods Kyongok Kang (FZ-Juelich)

  2. Introduction to Colloids What are Colloids? Colloidal particles are “aggregates” with linear dimensions in the size range of 1 nanometer – 20 microns colloids exhibit vivid thermal motion colloids are much larger than fluid molecules “Brownian motion” “hydodynamic interactions” sphere diameter 500 nm

  3. water molecules colloid Introduction to Colloids What are Colloids? Colloidal particles are “aggregates” with linear dimensions in the size range of 1 nanometer – 20 microns colloids exhibit vivid thermal motion sphere diameter 500 nm

  4. water molecules colloid Introduction to Colloids What are Colloids? Colloidal particles are “aggregates” with linear dimensions in the size range of 1 nanometer – 20 microns colloids exhibit vivid thermal motion Brownian motion is nothing but thermal motion Same laws of Thermodynamics and Statistical Physics Phase transitions You don’t have to learn anything new to understand colloids (in principle) sphere diameter 500 nm

  5. Direct interactions can be tuned “at will” V(r) - - - - - - - - - - - - - - - - - - - - - - - r Crystallization (FCC) Glasses Liquid-gas coexistence Aggregation Gels Crystallization (FCC and BCC) Electric fields

  6. Crystallization of “hard spheres” P.N. Pusey, E. Zaccarelli, C. Valeriani, E. Sanz, W.C.K. Poon, M.E. Cates, Phil.Transactions A, 367, 4993 (2009); arXiv:0908.1663v1 [cond-mat. Mtrl-sci]

  7. fluid gel “sticky spheres” binodal spinodal (taken from Eric Weeks webpage) H. Verduin, J.K.G. Dhont, J. Coll. Int. Sci. 172, 425 (1995)

  8. - - - - - - - - - - - - - - - - - - - - - - - Mixture of charged and uncharged colloids NaCl-type crystal NiAs-type crystal M.E. Leunissen et al., Nature 437, 235 (2005)

  9. Other shapes : rod-like colloids fd virus : L = 880 nm D = 7 nm P = 3000 nm

  10. Mixtures of rods and spheres Sphere diameter 100 nm Rod length 900 nm Adams et al., Nature,1998

  11. From David pine’s webpage disks patchy colloids F.M. van der Kooij, M. Vogel, H.N.W. Lekkerkerker, Phys. Rev. E 62, 5397 (2000) from David Pine’s webpage star-like polymers (like DNA-colloids) transient, non-equilibrium forces

  12. -COOH -COOH -COO- -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COOH -COO- -COO- -COOH -COOH -COOH -COO- -COOH -COO- -COO- -COOH -COOH -COO- -COO- -COOH -COOH -COOH -COO- -COO- -COOH -COOH -COO- -COOH Electric double layer / layer of condensed ions : 1 nm-10 micron minimization of F=U -TS dissociation : high S high U no dissociation : low S low U H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

  13. charge density Debye length screening length Electric double layer

  14. thin layer of “condensed” ions diffuse electric double layer

  15. - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + Electric-field induced phases, dynamical states , and critical behaviour in suspensions of rod-like charged colloid At sufficiently low frequencies (< 10 kHz): - double layers are polarized - the layer of condensed ions is polarized - field-induced association-dissociation of condensed ions - electro-osmotic flow is induced Field-induced colloid-colloid interactions : - electrostatics - hydrodynamics E

  16. fd virus : L = 880 nm D = 7 nm P = 3000 nm - 0.16 mM TRIS/HCl buffer (Debye length is 27 nm) - fd concentration is 2.0 mg/ml = within the isotropic-nematic two-phase region - At high ionic strength, the nematic phase is a cholesteric

  17. 10 x isotropic nematic Concentration : 2.0 mg/ml two-phase, isotropic-nematic coexistence = 26 c* function generator light source L = 1.5 mm polarizer analyzer G sample DIC CCD K. Kang, J.K.G. Dhont, Soft Matter 6, 273 (2010)

  18. 200 micron Nematic + Isotropic

  19. 200 micron a chiral nematic is also found at high ionic strengths and at higher f-concentration without an electric field Nematic + Chiral-nematic

  20. 200 micron Uniform homeotropic alignment

  21. 200 micron Uniform homeotropic alignment order parameter (S=0.48) and diffusion coefficients are independent of field strength and frequency no charge-polarization

  22. 200 micron Melting and forming of nematic domains

  23. association of condensed ions E 0 decay towards the isotropic state (ii) (iii) aligned state is unstable rotation of the director towards the external field decrease of ionic strength increase of ionic strength dissociation of condensed ions de-aligned state is meta-stable or unstable (iv) orientational order increases (v) (i) Origin of the dynamical state:

  24. 200 micron Critical behaviour: - Domain size diverges - Characteristic time for melting/forming diverges

  25. I t “video-image correlation function”: characteristic time for melting/forming

  26. E : power-law d: power-law : power-law d: logarithmic H D : logarithmic d: finite N*

  27. Polarization for parallel orientation only important when : frequency of the external field time to diffuse over the length of the rod diffusion coefficient of salt ions Hydrodynamic interactions are instantaneous when : Long rods : specific mass time for a shear wave to propagate of a distance shear viscosity

  28. hydrodynamic interactions (neglect polarization) polarization (neglect hydrodynamic interactions)

  29. Smoluchowski equation: (or : “the overdamped Liouville equation”) direct interactions hydrodynamic interactions gradient operator pdf for positions and orientations rotation operator diffusion-migration on a surface Theory low frequencies - polarization of a single particle (cooperation with Jerry Manning) - calculation of the pair-interaction forces - include these forces in the Smoluchowski equation (no HI: ) - account for the field-induced association-dissociation of condensed ions high frequencies (cooperation with Bogdan Cichocki) - flow induced by a single, unperturbed equilibrium double layer - “active” hydrodynamic interaction functions - analyze the Smoluchowski equation + “active” hydrodynamic + unperturbed direct interactions

  30. N*-formation kinetics after a frequency quench from the H-phase 200 um movies are 10 times accelerated

  31. Thank you for your attention 200 um movies are 10 times accelerated

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