Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session A42: Focus Session: Directed Assembly of Hybrid Nanomaterials |
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Sponsoring Units: DPOLY Chair: Sanat Kumar, Columbia University Room: A302/303 |
Monday, March 21, 2011 8:00AM - 8:12AM |
A42.00001: Magnetically Actuated Artificial Cilia with Controlled Length and Areal Density Jason Benkoski, Jennifer Breidenich, Michael Wei, Guy Clatterbaugh, Pei-Yuin Keng, Jeffrey Pyun Artificial cilia have been explored for use in microrobotics, MEMS, and lab-on-a-chip devices for applications ranging from micromixers, microfluidic pumps, locomotion, acoustic detection, and heat transfer. We have previously demonstrated the ability to assemble dense brushes of magnetically actuated artificial cilia from the dipolar assembly of 24 nm ferromagnetic cobalt nanoparticles. Despite areal densities exceeding 1 cilim/$\mu$m$^{2}$, diameters below 25 nm, aspect ratios exceeding 400, and flexural rigidities below 3 x 10$^{-28}$ Nm$^{2}$, these seemingly delicate structures resist collapse upon each other or the underlying substrate. The current study demonstrates the ability to rationally control their average length and areal density by changing the nanoparticle concentration and the dimensions of the rectangular capillary tube. We find that the length and areal density obey a simple conservation of mass relationship with concentration and capillary height such that the product of the former equals the product of the latter. Detailed statistical analysis supports a mechanism in which the role of the external field is to align pre-existing chains with the external field, assist stacking of chains along the axis of the field, and then draw them towards the ends of the permanent magnets, where the magnetic field gradient is steepest. [Preview Abstract] |
Monday, March 21, 2011 8:12AM - 8:24AM |
A42.00002: Ordered ferrofluidic assemblies in polymer film formed by magnetically induced polymer-solvent phase separation Nataraj Sanna Kotrappanavar, Myunghwan Byun, Paul Zaval-Reviera, Kevin Chonnon, Shaheen S.A. Al-Muhtaseb, Easan Sivaniah Tri-block copolymer has been used as nonferrofluid to generate permanent magnetic structures with controlled dimension and architecture in a partially miscible ferrofluid-nonferrofluid mixture under the influence of a perpendicular magnetic field. The nature of the resultant assemblies was strongly dependent on the magnetic field and concentration of ferro/nonferrofluidic systems. These ordered cluster assemblies in a polymer film that can be used either directly, in applications such as membrane, or subsequently as a template for the formation of other nanostructured materials. The origin of the permanent structures, which have characteristic lateral dimensions ranging from 5 $\mu$m to submicron range, is the repartitioning of the ferrofluid carrier solvent into the nonferrofluid polymeric phase. [Preview Abstract] |
Monday, March 21, 2011 8:24AM - 8:36AM |
A42.00003: Manipulating nanoparticles via polymer crystallization Christopher Li, Bin Dong, Bing Li, Xi Chen, Wenda Wang Directed nanoparticle (NP) assembly is of great interest in order to achieve desired NP structures for various application purposes. In this presentation, we will present our recent results on employing polymer single crystals (PSC) to direct NP assembly. First, tailor-made, free-standing NP frames and wires containing single or multiple types of NPs have been obtained by using an in-situ polymer crystallization method. End functionalized poly(ethylene oxide) single crystals were used as the templates. Gold and magnetite NPs were successfully patterned as evidenced by transmission electron microscopy experiments. Secondly, carbon nanotube induced PSCs were used to guide AuNPs to assemble into periodic pattern with controlled periodicity. Thirdly, polymer nanofibers decorated with block copolymer single crystals were used as templates to induce the formation of hydroxyapatite (HA) nanocrystals and the resultant nanofiber/HA hybrids mimic the structure of natural bones. [Preview Abstract] |
Monday, March 21, 2011 8:36AM - 9:12AM |
A42.00004: Directed Assembly of Nano-Colloids: Toward Discrete and Defined Polymer-Inorganic Architectures Invited Speaker: Analogies between controlled flocculation and the chemistry of macromolecular polymerization are informing new methods for bottom up fabrication of discrete polymer-inorganic architectures. Conceptually, hybrid nano-colloids with a narrow distribution of composition and structure (``monomers'') are assembled via external control of the agglomeration kinetics (``polymerization''). The challenge however is to impart a level of predictability between nanoparticle design and resultant assembly, as embodied in monomer design and macromolecular architecture. Depending on the magnitude and directionality of the interparticle interactions, the controlled assembly of these hybrid nano-colloids can span from discrete, soluble proto-assemblies to single-component, bulk mediums with local order ranging from liquid-like to long-range translational coherence. Using nanoparticle shape, organic corona structure, and processing conditions (e.g. modulating the stability of the nano-colloid via solvent quality rather than number density), we demonstrate the fabrication of various discrete and defined metallic and metal oxide hybrid architectures, and discuss the unique properties of the assemblies, which reflect the uniformity of structure, nano-scale separation of the inorganic particles, and confinement of the polymer chains. [Preview Abstract] |
Monday, March 21, 2011 9:12AM - 9:24AM |
A42.00005: Designing Functionalized Nanoparticles for Controlled Assembly in Polymer Matrix: Self consistent PRISM Theory and Monte Carlo simulation Study Arthi Jayaraman, Nitish Nair Significant interest has grown around the ability to create hybrid materials with controlled spatial arrangement of nanoparticles mediated by a polymer matrix. By functionalizing or grafting polymers on to nanoparticle surfaces and systematically tuning the composition, chemistry, molecular weight and grafting density of the grafted polymers one can tailor the inter-particle interactions and control the assembly/dispersion of the particles in the polymer matrix. In our recent work using self-consistent Polymer Reference Interaction Site Model (PRISM) theory- Monte Carlo simulations we have shown that tailoring the monomer sequences in the grafted copolymers provides a novel route to tuning the effective inter-particle interactions between the functionalized nanoparticles in a polymer matrix. In this talk I will present how monomer sequence and molecular weights (with and without polydispersity) of the grafted polymers, compatibility of the graft and matrix polymers, and nanoparticle size affect the chain conformations of the grafted polymers and the potential of mean force between the grafted nanoparticles in the matrix. [Preview Abstract] |
Monday, March 21, 2011 9:24AM - 9:36AM |
A42.00006: High Fidelity Detection of Defects in Polymer Films using Surface-Modified Nanoparticles Alamgir Karim, Matthew Becker, Chaitanya Pratiwada Surface defects are ubiquitous for most thin films, yet their systematic detection poses one of the most difficult challenges even to modern day technology. Polymer thin films are no exception to these problems. We address this issue by developing a novel, efficient method for the optical detection of surface topographical features using fluorescent nanoprobes, which are surface-modified CdSe quantum dots whose ability to detect surface features can be tuned via size and chemical properties. We have successfully applied this approach to detect numerous types of artificial and natural defects in polymer films including lines, pinholes, sharp edges, and chemically variant defect surfaces. This method can elucidate the surface structure of large areas in a minimal amount of time. It is estimated that this new method will decrease imaging time compared to traditional imaging methods like AFM and SEM by 50 fold. Our defect detection approach could be applicable for many problems where polymers are used as a component in hybrid nanomaterial films [Preview Abstract] |
Monday, March 21, 2011 9:36AM - 9:48AM |
A42.00007: Directed Hierarchical Assemblies of Nanoparticles in Thin Films Ting Xu Controlling nanoparticle (NP) assemblies in thin films will enable one to capitalize on the unique properties of NPs so as to generate functional devices, such as hybrid photovoltaic, capacitors and optical devices. To this end, it is mandatory to control the macroscopic alignment of NP assemblies and inter-particle ordering with high precision to achieve a specific property. Recently, we described a new approach to assemble NPs over multiple length scales by combining small molecules with block copolymers (BCPs). Small molecules that favorably interact with NP ligands mediate polymer-NP interactions and solublize the NPs within the BCP microdomains. The small molecules also direct the spatial distribution of NPs within the BCP microdomains with exquisite precision. In the bulk, NPs were shown to readily assemble into ordered 1-D, 2-D and 3-D arrays. I will discuss our recent studies on directed hierarchical assemblies of NPs in thin films. Specifically I will focus on how to manipulate the macroscopic alignment and long-range ordering of NPs and generating NP superlattice within the BCP microdomains. [Preview Abstract] |
Monday, March 21, 2011 9:48AM - 10:24AM |
A42.00008: Adsorption of particles at fluid interfaces: Jamming, structure control, and rheology Invited Speaker: Various types of particles readily adsorb at the interface between two immiscible liquids or at the surface of a liquid. Such particles bear some similarity to conventional molecular surfactants. However, unlike surfactants, particles adsorb almost irreversibly at interfaces - a fact that can lead to interesting phenomena such as the stability of non-spherical jammed drops, spontaneous climbing of particle films, and particle-bridged emulsions. Similar phenomena - albeit with important differences - can be observed in polymeric systems and may lead to interesting new materials. This talk will review some of these phenomena, with a particular focus on the jamming of fluid interfaces due to particles, and discuss applications for controlling the structure of two-phase polymer systems such as polymer blends and foams. [Preview Abstract] |
Monday, March 21, 2011 10:24AM - 10:36AM |
A42.00009: Additive-driven assembly of block copolymers Ying Lin, Vikram Daga, Eric Anderson, James Watkins One challenge to the formation of well ordered hybrid materials is the incorporation of nanoscale additives including metal, semiconductor and dielectric nanoparticles at high loadings while maintaining strong segregation. Here we describe the molecular and functional design of small molecule and nanoparticle additives that enhance phase segregation in their block copolymer host and enable high additive loadings. Our approach includes the use of hydrogen bond interactions between the functional groups on the additive or particle that serve as hydrogen bond donors and one segment of the block copolymer containing hydrogen bond acceptors. Further, the additives show strong selectively towards the targeted domains, leading to enhancements in contrast between properties of the phases. In addition to structural changes, we explore how large changes in the thermal and mechanical properties occur upon incorporation of the additives. Generalization of this additive-induced ordering strategy to various block copolymers will be discussed. [Preview Abstract] |
Monday, March 21, 2011 10:36AM - 10:48AM |
A42.00010: Supramolecular Assembly of Gold Nanoparticles in PS-b-P2VP Diblock Copolymers via Hydrogen Bonding Se Gyu Jang, Craig J. Hawker, Edward J. Kramer We report a simple route to control the spatial distribution of Au nanoparticles (Au-NPs) in PS-$b$-P2VP diblock copolymers using hydrogen bonding between P2VP and the hydroxyl-containing (PI-OH) units in PS-$b$-PIOH thiol-terminated ligands on Au-NP. End-functional thiol ligands of poly(styrene-$b$-1,2{\&}3,4-isoprene-SH) are synthesized by anionic polymerization. After synthesis of Au-NPs, the inner PI block is hydroxylated by hydroboration and the resulting micelle-like Au-NPs consist of a hydrophobic PS outer brush and a hydrophilic inner PI-OH block. The influence of the hydroxyl groups is significant with strong segregation being observed to the PS/P2VP interface and then to the P2VP domain of lamellar-forming PS-b-P2VP diblock copolymers as the length of the PI-OH block is increased. The strong hydrogen bonding between nanoparticle block copolymer ligands and the P2VP block allows the Au-NPs to be incorporated within the P2VP domain to high Au--NP volume fractions $\phi _{p }$without macrophase separation, driving transitions from lamellar to bicontinuous morphologies as $\phi _{p}$ increases. [Preview Abstract] |
Monday, March 21, 2011 10:48AM - 11:00AM |
A42.00011: Role of defects on self-assembly of nanoparticles in block copolymer thin film Jenny Kim, Peter Green The structure of A-b-B block copolymer (BCP) thin films is often exploited as scaffolds for directing nanoparticles into various, long-range ordered geometries. Depending on the affinity between nanoparticles and block chains, nanoparticles preferentially segregate to either A or B domains. We show that dislocations may play a dominant role in the assembly of large nanoparticles in BCP thin film that order at suboptimal thicknesses. Edge dislocations are ubiquitous in lamellar BCP thin films forming a partial surface layer, i.e. holes or island structures. When the ratio of the nanoparticle diameter, d, to the domain dimension, L, d/L $<$ 0.15, the nanoparticles were distributed uniformly throughout the film. However for larger values of d/L, the nanoparticles reside primarily at the dislocation cores. In the case of films of initial film thicknesses between L $<$ h $<$ 3L the nanoparticles self-assemble into 2-dimensional planar shapes at the boundaries of holes or islands where edge dislocations are located. [Preview Abstract] |
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