1. Self-Assembly of Two-Dimensional Multi-Component Colloidal Lattices at Liquid Interfaces HuanMa and Lenore L. Dai October 2009

2. Photonic bandgap crystals Chemical sensors Optical devices Porous membranes Masks or templates for nanostructure fabrications Applications of Colloidal Crystals 2 Colloidal crystals in polymer networks Structure obtained by colloidal crystal templating Zakhidov, A. A. et al. Science1998, 282, 897-901. Pan, G. S. et al. Phys. Rev. Lett. 1997, 78, 3860-3863.

3. Potential Impacts to Related Research Biology: Protein particles in the surface layers (S-layers) of bacteria or archaea Physics: Phase transitions with molecular and “atomic” resolution Premelting at a grain boundary Alsayed, A. M. et al. Science2005, 309, 1207-1210. 3 S-Layer lattice types Sleytr, U.B. et al. Prog. Surf. Sci.2001, 68, 231-278. 5 µm

4. Hexagonal lattice structure Close packed Non-close packed One-component 2D Colloidal Lattices Particle dynamics Particle interactions Lattice stability Phase transitions 4 Close packed colloidal lattice consists of carboxy-coated polystyrene particles Non-close packed colloidal lattice consists of sulfate treated polystyrene particles 2 1 3 4 5 4 µm 10 µm Binks, B. P.; Rodrigues, J. A. Angew. Chem. Int. Ed. 2005, 44, 441-444. Tarimala, S.; Wu, C.; Dai, L. L. Langmuir 2006, 22, 7458-7461.

5. Motivations Multi-component 2D colloidal lattices Rich lattice structures The computational predictions could hardly be validated experimentally Difficulty in controlling the particle size and number ratios in experiments Interaction models in the simulations are still under development 5 Disordered at NS:NL = 7:1 Ordered at NS:NL = 2:1 Simulation result: 0.89 µm / 2.7 µm Stirner, T.; Sun, J. Z. Langmuir 2005, 21, 6636-6641.

7. Preparing Pickering Emulsions Materials Water (HPLC, Acros Organics) Poly(dimethylsiloxane)(PDMS, Rohodorsil Fluid 47V5, 5 cSt at 25 °C) Negatively charged FluoSpheres® fluorescent microspheres from Molecular Probes™ (~1 µm in diameter, 2% dispersion in distilled water with 2 mM sodium azide) Ultrasonic processor (Sonics Vibracell, 500 W model) 7

9. Sequential imaging functionPrasad, V. et al. J. Phys.: Condens. Matter2007, 19, 113102. 8

10. Langmuir-Blodgett TroughInstrument and Experimental Method NIMA 612D Trough Material: Teflon Area range: 45 - 600 cm2 Speed range: 7.1 - 828.5 cm2/min Symmetrical compression with two barriers Pressure sensor: a filter paper plate Sample 0.8% particle dispersions in isopropanol/water (5:1) mixture Method Inject to the air/water interface dropwise using a 250 µL Hamilton syringe 9

12. One-Component Colloidal Lattices 11 AS-PS S-PS Particles oscillate around their equilibrium positions Inset FFTs: six distinct first order peaks indicate long-range order Particle aggregates coexisting with the lattice structure

13. Two-Component Colloidal Lattices 12 S-PS dominated lattice Lattice without dominating species No distinct phase separation of different particle types in the lattice Inset FFTs: the diffuse ring indicates lower degree of lattice order AS-PS dominated aggregates

15. AS-PS form largely fivefold defectsSixfold

16. Interparticle Distances 14 The two-component system seems to have a broader interparticle distance distribution than the one-component systems

17. Force Calculation Determine 15

18. Coulomb Force 16 Assumptions: 1 Particle size >>Debye length (22.3 nm) 2 Contact angle not very small Area of particle-oil interface: Surface charge density at particle-oil interface: σpo Dimensionless distance between particle centers: Particle radius: R Contact angle measured through the water phase: θ Dielectric constant of oil: ε Permittivity of vacuum: ε0 oil water Aveyard, R. et al. Langmuir 2000, 16, 1969-1979.

19. Capillary Force Undulations of the three-phase contact line (wetting property of the particle) Interfacial tension of oil-water interface: γow = 44.6 mN/m Amplitude of the three-phase contact line undulations: δ 50 nm for particle size 1 µm 17 Stamou, D. et al. Physical Review E 2000, 62, 5263-5272. Horozov, T. S. Langmuir2005, 21, 7405-7412.

20. Other Negligible Forces Dipolar forces Dipoles at particle-oil interfaces (Fdipole-oil) Asymmetric distribution of the free ions (Fdipole-water) Capillary forces Electostatic field Gravity (Fcapillary-gravity) Van der Waals forces (Fvander Waals) 18

21. Ftotal versus σpo Ftotal between any pair of particles is repulsive and equal in a colloidal lattice at equilibrium 19 * For degree of surface ionization at particle-oil interface αpo = 0.01 Aveyard, R. et al. Langmuir2000, 16, 1969-1979.

22. Summary One- and two-component colloidal lattices were successfully assembled at poly(dimethylsiloxane)-water interfaces in Pickering emulsions The colloidal particles assemble into long-range ordered structure and oscillate around their equilibrium positions Different types of particles distribute randomly in the lattice with no obvious phase separation In the two-component colloidal lattices, the S-PS particles form mostly 6-fold lattice sites, whereas the AS-PS particles largely form 5-fold defect sites In addition, we have performed total force calculations and extrapolated the surface charge density at the particle-oil interface 20

23. Acknowledgements The W. M. Keck Bioimaging Laboratory for confocal microscope usage The Department of Scientific Computing at the Florida State University for the Voronoi diagram Matlab program National Science Foundation (CBET-09063570) 21

24. Questions? Thanks! 22