Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session T3: Materials with Topological Defects on Gaussian Curved Surfaces |
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Sponsoring Units: DCMP DPOLY Chair: Paul Chaikin, New York University Room: Oregon Ballroom 203 |
Wednesday, March 17, 2010 2:30PM - 3:06PM |
T3.00001: Structure and Stability of Defect Arrays on Curved Interfaces Invited Speaker: In a wide variety of physical systems over many length scales one encounters interfaces or intrinsic two-dimensional surfaces that are curved. Condensed matter order on these surfaces has several novel features not encountered in flat space, including the presence of topological defects in the ground state that would normally only be excited states on planar surfaces, and the instability of otherwise stable configurations such as interstitials. I will discuss the structure and stability of these defect arrays as a function of the geometry and topology of the surface, the nature of the long range order itself and the number of ordering units. Since defects are prime candidates for sites to attach ligands via functionalization, this understanding may aid in the design of mesoscale ``atoms'' which themselves can self-assemble into novel mesoscale molecules and in turn bulk materials. I will emphasize several physical systems, including colloidal droplets and block copolymer vesicles, in which defect arrays may be imaged and the above ideas explored. [Preview Abstract] |
Wednesday, March 17, 2010 3:06PM - 3:42PM |
T3.00002: Scars on Spherical Colloidosomes Invited Speaker: |
Wednesday, March 17, 2010 3:42PM - 4:18PM |
T3.00003: Topological defects in colloidal Wigner crystals on curved surfaces Invited Speaker: Charged hydrophobic (PMMA) colloids in an oil phase (cyclohexyl bromide) are attracted, without wetting, by image charge effects to an oil-water interface. The micron size spheres form a monolayer and interact via screened coulomb interactions to form a crystalline lattice. By creating curved oil-water interfaces having positive, negative and varying Gaussian curvature as well as different Euler numbers, we study the influence of curvature on the distribution and dynamics of topological defects. We image and manipulate the full crystal on the curved surface using a setup capable of simultaneous holographic optical tweezing and confocal imaging. [Preview Abstract] |
Wednesday, March 17, 2010 4:18PM - 4:54PM |
T3.00004: Self-assembly on curved surfaces: the formation of divalent nanoparticles through topological constraints Invited Speaker: It is known that thiolated molecules spontaneously form poly-crystalline self-assembled monolayers (SAMs) on flat gold surfaces. Scanning tunneling microscopy (STM) studies have shown that, in SAMs composed of more than one type of molecule (mixed-SAMs), domains of random shape and size phase-separate. Here we will show that, when mixed SAMs are formed on gold nano-crystals with a radius of curvature $<$ 20 nm, they spontaneously phase-separate into highly ordered domains of unprecedented size. In the case of binary mixture of thiolated ligands on gold particles, domains, only 0.5 nm wide, of alternating composition encircling or spiraling around the metallic core spontaneously assemble. This new family of nano-structured nano-materials shows properties that are determined by this unique morphology, such as solubility. In particular we will show that the order in the ligand shell of these particles imposes the topological presence of at least two diametrically opposed point defects that can be chemically functionalized so to form divalent metal nanoparticles. [Preview Abstract] |
Wednesday, March 17, 2010 4:54PM - 5:30PM |
T3.00005: Experimental Studies of Defects in (Co)polymer Nanosystems Invited Speaker: We presented an approach of creating surfaces with Gaussian curvature gradients by using commercially available colloidal particles and standard processing techniques. We also demonstrated that these non-flat surfaces can induce regions of both high order has well as disorder in cylindrical block copolymer films depending on the Gaussian curvature of the surface. On a flat surface the ground state has no preferential direction and a high density of disclinations is observed. A Gaussian curvature destroys the isotropy in alignment and induces a preferential alignment. For small bumps the cylinders wrap around the top of the bump with a constant density of disclinations and dislocations as a function of distance from the top. Larger bumps show a disordered phase in a region on the top of the bump. The disorder is induced by the migration of disclinations towards the top of the bump. [Preview Abstract] |
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