Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J5: Polymer Nanoparticle Interactions |
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Sponsoring Units: DPOLY Chair: Thomas Russell, University of Massachusetts Room: 401/402 |
Tuesday, March 17, 2009 11:15AM - 11:51AM |
J5.00001: Simulations of Polymer Grafted Nanoparticles in a Polymer Matrix Invited Speaker: We have performed molecular dynamics (MD) simulations of polymer-grafted nanoparticles in a polymer melt. The model is a coarse-grained representation of spherical nanoparticles with a grafted poly(methyl methacrylate)-like bead-spring polymer in a matrix of the same polymer. Simulations were performed on both a single polymer-grafted nanoparticle as well as for a pair of polymer-grafted nanoparticles. The nanoparticle has a diameter of 5 nm. We have investigated the role of the molecular weight of the grafted and matrix polymer on both brush structure and nanoparticle-nanoparticle interactions. We find that brush density profile is independent of matrix molecular weight. Furthermore, the matrix chains penetrate almost to the particle surface, and there is no extended region with zero or near-zero matrix chain density. Hence, the highly curved brush does not exhibit ``dry brush'' behavior that would be expected at this investigated grafting density. We observe a repulsive interaction between the nanoparticles that sets in at a separation consistent with the polymer brush height. The combined brush-brush plus matrix effect on the nanoparticle-nanoparticle interactions is repulsive at all separations. Our simulations profile reveals no matrix-induced attraction between nanoparticles that is anticipated when the brush are truly ``dry'', i.e., largely non-penetrable by the matrix. Such behavior would be expected for larger particles where the surface curvature effects on brush structure and brush-melt interactions are less important. However, for small nanoparticles, our simulations reveal that surface curvature effects are very important in determining the structure of the grafted polymer as well as nanoparticle-nanoparticle interactions. [Preview Abstract] |
Tuesday, March 17, 2009 11:51AM - 12:27PM |
J5.00002: Interaction, Structure and Transport of Polymer Grafted Nanoparticles Invited Speaker: Grafting polymers to nanoparticles has proven to be an effective means to disperse isotropic and anisotropic nanoparticles in polymer matrices. Depending on the grafting density, polydispersity and nature of polymer - nanoparticle interaction, such grafted nanoparticles can either be liquid-like, gel-like or crystalline solids. We examine here the nature of interactions between such grafted nanoparticles and correlate those to the structure, dynamics and transport in both solvent and polymer media. [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 1:03PM |
J5.00003: Modification of Block Copolymers Using Surface-Functionalized Hard and Soft Nanoparticles Invited Speaker: Due to their wide range of available nanostructures, ordered block copolymers provide excellent templating media into which nanoparticles can be incorporated with precise spatial modulation for various nanotechnologies. Previous experimental and theoretical studies have demonstrated that the relative size and selectivity of surface-functionalized inorganic nanoparticles can be used to tune the position of the nanoparticles along interfacial regions or within microdomains. Using a combination of experimental and theoretical methods, we furthermore show that these parameters, in addition to nanoparticle concentration, can be used to controllably alter the phase stability of block copolymers. While nanoparticles typically reduce the order-disorder transition (ODT) temperature of ordered block copolymers, a limited window exists wherein the nanoparticles increase the ODT temperature and stabilize the copolymer nanostructure. This nanoparticle-mediated design is extended in this study to include ``soft'' nanoparticles composed of core-shell microgels (CSMG) particles, which can be envisaged as permanent micelles. Addition of CSMG particles to ultrathin films consisting of ordered block copolymers varying in morphology and molecular weight is investigated here by electron microscopy. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:39PM |
J5.00004: Polymer single crystal meets nanoparticle, toward ordered hybrid materials Invited Speaker: Judiciously selected polymer single crystal (PSC) systems can interplay with 1-D and 0-D nanoparticles, forming ordered hybrid structures. In this presentation, I will first focus on patterning PSCs on individual carbon nanotubes (CNT). Using both controlled solution crystallization, thin film crystallization and physical vapor deposition methods, CNTs were periodically decorated with PSCs, resulting in nano hybrid shish-kebab (NHSK) structures. Because the polymer kebabs can be easily removed, these unique NHSKs can serve as templates to fabricate a variety of CNTs-containing hybrid materials with controlled pattering on the CNT surface. Sub-20 nanometer alternating patterning was achieved by using crystalline block copolymers. The mechanism was attributed to the crystallization induced block copolymer phase separation. This pattern was successfully used to template nanoparticles (NP) pattering on CNTs. In the second part of the talk, I will discuss fabricating Janus NPs and patterning these NPs using PSCs. Single crystals of thiol-terminated polyethylene oxide (PEO) were incubated in a gold sol. Au-S bonds were formed between the AuNPs and the PEO single crystal surfaces. The inter-particle spacing was controlled by PEO molecular weights, the incubation time, and the annealing temperatures after incubation. The planar geometry of the PSCs led to Janus NP formation. A series of NP dimers, trimers and tetramers were synthesized. NP nanowires were also fabricated. We anticipate that this observation could lead to controlled synthesis of artificial molecules and NP chains for a variety of optical, electronic, and biomedical applications. [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 2:15PM |
J5.00005: DNA Directed Nanoparticle Assemblies Invited Speaker: While DNA is mostly noted for carrying genetic information, a single strand of DNA is simply a polymer with chemically specific recognition. As a result, DNA is an interesting polymer to consider for the development of new materials. In particular, attaching single strands of DNA to nanoparticles offers the possibility to encode highly specific bonding between nanoparticles to create engineered building blocks, or ``functionalized atoms.'' These core units are an ideal candidate for the development of network-based, nanostructured materials. In this talk, we present results from computer simulations of a coarse-grained model examining several choices and DNA functionalization, and show how these design choices can affect dynamics, phase behavior, and the formation of crystal structures. We first discuss nanoparticles functionalized by four single DNA strands. These units give rise to a material with a hierarchy of interpenetrating networked structure and four thermodynamically distinct amorphous phases, unlike any naturally occurring pure material. On the other hand, the mechanism for the formation of the amorphous phases offers insight into anomalous networked liquids like water and silica. We also consider how varying the number of functionalizing DNA strands alters both the number and shape of these phase transitions. The formation of very low density crystals of nanoparticles tethered by DNA has recently been achieved experimentally, but the factors controlling crystal formation are still not well understood. Therefore, we also discuss the results of nanoparticles uniformly coated with DNA, similar to experimental systems. We show how the DNA strand length and stiffness affects the competition between energy and entropy that controls crystal formation. [Preview Abstract] |
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