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2006
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Horsch MA, Zhang ZL, Glotzer SC
Simulation studies of self-assembly of end-tethered nanorods in solution and role of rod aspect ratio and tether length
JOURNAL OF CHEMICAL PHYSICS 125 (18): Art. No. 184903 NOV 14 2006
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We present temperature versus concentration phase diagrams for "shape amphiphiles" comprised of tethered moderate and low aspect ratio rods. Simulations of moderate aspect ratio rods (first reported by Horsch [Phys. Rev. Lett. 95, 056105 (2005)]) predict their self-assembly into spherical micelles with bcc order, long micelles with nematic order, a racemic mixture of hexagonally ordered chiral cylinders, two perforated phases: one with tetragonal order and one with hexagonal order, and a smectic C lamellar phase. In contrast, we predict here that small aspect ratio tethered rods self-assemble into bcc ordered spherical micelles, hexagonally ordered cylinders, and a smectic C lamellar phase. We compare and contrast the phases obtained for the two aspect ratios and examine in further detail several unusual phases. Our simulations also reveal that for moderate aspect ratio rods there is a tendency toward phases with decreasing interfacial curvature with decreasing coil size, including a double gyroid phase. In addition, we investigate the role of tether length on the assembled structures. Our results are applicable to short rod-coil block copolymers and rodlike nanoparticles with polymer tethers, and to colloidal building blocks comprised of a flexible string of colloids tethered to a rigid string of colloids, with the interactions scaled appropriately.
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Horsch MA, Zhang ZL, Glotzer SC
Self-assembly of laterally-tethered nanorods
NANO LETTERS 6 (11): 2406-2413 NOV 8 2006
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We report results from a computational study of laterally tethered nanorod "shape amphiphiles". Our simulations predict that the model nanorods self-assemble into stepped-ribbon-like micelles, a centered rectangular stepped-ribbon phase, and two structurally different liquid crystalline bilayer phases: one in which the bilayers have C-mm symmetry and another in which they have P-2 symmetry. We provide a possible explanation for the transition between the two C-mm and P-2 liquid crystalline phases.
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Tang ZY, Zhang Z-L, Wang Y, Glotzer SC, Kotov NA
Self-assembly of CdTe nanocrystals into free-floating sheets
SCIENCE 314 (5797): 274-278 OCT 13 2006
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In their physical dimensions, surface chemistry, and degree of anisotropic interactions in solution, CdTe nanoparticles are similar to proteins. We experimentally observed their spontaneous, template-free organization into free-floating particulate sheets, which resemble the assembly of surface layer (S-layer) proteins. Computer simulation and concurrent experiments demonstrated that the dipole moment, small positive charge, and directional hydrophobic attraction are the driving forces for the self-organization process. The data presented here highlight the analogy of the solution behavior of the two vastly different classes of chemical structures.
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Chan ER, Ho LC, Glotzer SC
Computer simulations of block copolymer tethered nanoparticle self-assembly
JOURNAL OF CHEMICAL PHYSICS 125 (6): Art. No. 064905 AUG 14 2006
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We perform molecular simulations to study the self-assembly of block copolymer tethered cubic nanoparticles. Minimal models of the tethered nanoscale building blocks (NBBs) are utilized to explore the structures arising from self-assembly. We demonstrate that attaching a rigid nanocube to a diblock copolymer affects the typical equilibrium morphologies exhibited by the pure copolymer. Lamellar and cylindrical phases are observed in both systems but not at the corresponding relative copolymer tether block fractions. The effect of nanoparticle geometry on phase behavior is investigated by comparing the self-assembled structures formed by the tethered NBBs with those of their linear ABC triblock copolymer counterparts. The tethered nanocubes exhibit the conventional triblock copolymer lamellar and cylindrical phases when the repulsive interactions between different blocks are symmetric. The rigid and bulky nature of the cube induces interfacial curvature in the tethered NBB phases compared to their linear ABC triblock copolymer counterparts. We compare our results with those structures obtained from ABC diblock copolymer tethered nanospheres to further elucidate the role of cubic nanoparticle geometry on self-assembly.