### Session B6: Control and Architecture in Directed Macromolecular Self-Assembly

 Monday, March 5, 2007 11:15AM - 11:51AM B6.00001: Geometry and universality in self-assembly Invited Speaker: Mark Bowick I will discuss the use of ideas from geometry and topology in combination with the statistical mechanics of self-assembly to classify the possible types of mesoatoms that can constitute a library of raw materials for making mesomolecules and bulk materials. I will concentrate on mesoatoms made up of an ordered two-dimensional monolayer of particles on the surface of a liquid droplet. Both the shape and the topology of the two-dimensional surface can be varied as well as the architecture of the ordering particles. The topology of the surface and the symmetries of the two-dimensional order severely restrict the possible defect structure of the mesoatom, which in turn fixes its valency. Defective regions are natural places for biological activity, chemical linking, unusual elastic response and aggregation of disorder. Specific examples include crystalline and hexatic order of point particles on the sphere, paraboloid, torus and Gaussian bump, nematic order of nematogens on the sphere and torus, and vector order of polar units on the sphere. The Gaussian curvature of the underlying surface may also lead to new features in the ground state, such as extended defect arrays of various kinds and curvature-driven defect unbinding, all of which may be exploited via engineered or spontaneous self-assembly. Monday, March 5, 2007 11:51AM - 12:27PM B6.00002: Colloidal atoms and molecules Invited Speaker: David Pine We describe two new types of colloidal particles that greatly expand the kinds of colloids and nanoparticles that are available for self-assembly. The first type, called colloidal molecules, consists of clusters of microspheres and/or nanospheres that take on well-defined geometries such as dumbbells, triangles, tetrahedra, octahedral, \textit{etc}. With these, we explore new two and three-dimensional phases, including dumbbells at a planar interface, and three-dimensional assemblies of tetrahedra. The second type, called colloidal atoms, consists of nearly spherical particles with a specific number of symmetrically-placed patches on their surface. These patches have symmetries similar to the colloidal molecules described above. The patches can be functionalized with single-stranded DNA that interacts specifically with complementary strands on other particles forming a network or crystal of colloidal particles. Monday, March 5, 2007 12:27PM - 1:03PM B6.00003: Colloidal Armor Invited Speaker: Howard Stone Assembly of colloidal particles on fluid-fluid interfaces is a promising technique for synthesizing two-dimensional structured materials. We describe a microfluidic method that allows direct visualization and understanding of the dynamics of the growth of colloidal crystals on a curved interface. We show how this approach allows control over composition and size of the colloidal armor, including making janus shells. The two-dimensional granular shells have mechanical properties similar to other elastic-plastic materials. These features will be described and the influence of surfactants on the shells will be presented. Finally, gas bubbles covered with colloidal particles show unusual stability against gas dissolution, and we will explore this stability using experiments and numerical simulations. Monday, March 5, 2007 1:03PM - 1:39PM B6.00004: Recent Advances in Solution-state Assembly of Synthetic Polymers into Well-defined Nanostructures. Invited Speaker: Karen Wooley The solution-state assembly of synthetic amphiphilic block copolymers has emerged as a powerful tool to conveniently and rapidly afford discrete, well-defined nanoscale materials for study and application to advance nanoscience and nanotechnology. One of the key challenges has been the identification of appropriate polymer components and conditions to control the assembly mechanisms and produce complex materials of uniform size, narrow size distribution and having interesting morphologies. In addition, developing systems that are capable of undergoing assembly directly from aqueous solution and also those that contain complex internal phase segregated domains ($i.e.$ multicompartment micelles) are significant interests. This presentation will provide an update on our work to control the micelle morphologies and will describe recent di- and tri-block copolymer designs that allow for pH-triggered self assembly into amphiphilic core-shell micelles, without the use of organic solvents. Moreover, the aqueous solution-state assembly of novel amphiphilic hyperbranched copolymers will be discussed. Monday, March 5, 2007 1:39PM - 2:15PM B6.00005: Non-ionic micelles and encapsulation. Invited Speaker: Paschalis Alexandridis The development of self-assembly as a useful approach to the synthesis and manufacturing of complex systems and materials is a central theme in our research. Amphiphilic block copolymers of the poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) family (commercially available as Poloxamers) are well-known for self-assembling into (core-shell spherical) micelles and (cubic, hexagonal, and lamellar) lyotropic liquid crystals in water. We are interested on how the aqueous phase behavior and structure of these non-ionic polymeric amphiphiles can be modulated by the addition of organic solvents or solutes. Our studies (i) probe the amphiphile organization in both micellar solutions and lyotropic liquid crystals, (ii) combine macroscopic observations (e.g., concentration-temperature micellization phase boundaries, ternary isothermal amphiphile-water-cosolvent phase diagrams) with microscopic measurements (from small-angle neutron and X-ray scattering), and (iii) aim to relate the type of structure formed and its properties to the relative swelling of the polymer blocks and to the location of the solvent/solute in the amphiphile assembly. These studies address the following practical questions: What are the right'' components and conditions for self-assembly? What if the conditions are no longer right''? How can we help'' self-assembly? Modulation of structure-property relationships in amphiphile-containing media is central to formulation of pharmaceutics and personal care products.