Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H4b: Depletion Forces In Vitro and Out of Equilibrium |
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Sponsoring Units: DCMP Chair: John Crocker, University of Pennsylvania Room: Baltimore Convention Center 308 |
Tuesday, March 14, 2006 1:03PM - 1:39PM |
H4b.00001: Entropically Driven Helix Formation Invited Speaker: We model the folding of helices via the depletion interaction between a semi-flexible tube and hard spheres. We find that the lowest-entropy geometry of the tube depends on both the concentration and size of the spheres. In the limit of small spheres, the helix becomes optimally tight, that is, maximally thick for a fixed length. We discuss this effect when both the tube and spheres are confined in a cylinder, as a model of the ribosomal channel. The depletion interaction alone forces the tube to lie against the wall, as opposed to the tight helix. Hydrophobicity and electrostatics can stabilize the compact tube and we estimate the strength of these effects necessary to favor a tight helix. [Preview Abstract] |
Tuesday, March 14, 2006 1:39PM - 2:15PM |
H4b.00002: Phase Behavior, Structure, and Assembly of Microsphere-Nanoparticle Mixtures. Invited Speaker: The phase behavior, structure, and assembly of microsphere-nanoparticle mixtures have been investigated. A new mechanism for regulating the stability of colloidal particles, known as nanoparticle haloing, has been identified in binary mixtures that possess both high charge and size asymmetry. Negligibly charged colloidal microspheres, which flocculate when suspended alone in aqueous solution, undergo a remarkable stabilizing transition upon the addition of critical volume fraction of highly charged nanoparticle species. Using confocal microscopy, we have characterized the structural evolution of colloidal phases formed during sedimentation on patterned and non-patterned substrates as a function of varying composition. Through nanoparticle engineering, we have created robust colloidal crystals that can be harvested from solution without introducing drying related defects as well as colloidal gels whose structure and rheological properties vary dramatically. [Preview Abstract] |
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