Pavan, M. J. ; Shenhar, R. Nanoparticle organisation into branched morphologies using thin films of crystalline polymers as dynamic templates. Journal of Materials Chemistry 2010, 20, 1247-1252.Abstract

We present a facile route for the fabrication of hierarchical, hyper-branched nanoparticle superstructures guided by a two-dimensional polymer template. Our approach utilises semi-crystalline poly(ethylene glycol) (PEG) films featuring branched arrays of channels as templates for the patterning of gold nanoparticles of different sizes and surface chemistry. The deposited nanoparticles preferentially adhere to the channel edges, forming nanoparticle chains decorating the contours of the surface topography. This preference is shown to be independent of nanoparticle size and surface chemistry; however, smaller nanoparticles appear to be more sensitive to subtle topographical attributes of the film. Additionally, the ability to induce the dissolution of the crystalline polymer domains during the nanoparticle patterning process leads to a controlled exchange of these domains with fractal nanoparticle arrays. This dynamic templating methodology adds another dimension to the toolbox of existing patterning methodologies.

21. Mariela JMC 2010   Journal of Materials Chemistry 2010

Eisenberg, D. ; Shenhar, R. ; Rabinovitz, M. Synthetic approaches to aromatic belts: building up strain in macrocyclic polyarenes. Chemical Society Reviews 2010, 39, 2879-2890.Abstract

This tutorial review discusses synthetic strategies towards aromatic belts, defined here as double-stranded conjugated macrocycles, such as [n]cyclacenes, [n]cyclophenacenes, Schluter belt, and Vogtle belt. Their appeal stems, firstly, from the unique nature of their conjugation, having p orbitals oriented radially rather than perpendicular to the plane of the macrocycle. Secondly, as aromatic belts are model compounds of carbon nanotubes of different chiralities, a synthetic strategy towards the buildup of structural strain in these compounds could finally open a route towards rational chemical synthesis of carbon nanotubes. The elusiveness of these compounds has stimulated fascinating and ingenious synthetic strategies over the last decades. The various strategies are classified here by their approach to the buildup of structural strain, which is the main obstacle in the preparation of these curved polyarenes.

22. David CSR 2010

Eisenberg, D. ; Jackson, E. A. ; Quimby, J. M. ; Scott, L. T. ; Shenhar, R. The Bicorannulenyl Dianion: A Charged Overcrowded Ethylene. Angewandte Chemie-International Edition 2010, 49, 7538-7542.Abstract

Super bowl: Bicorannulenyl, a large biaryl composed of two corannulene bowls, effectively becomes an overcrowded ethylene upon reduction to form a dianion (see picture). DFT calculations and NMR spectroscopic experiments reveal the double‐bond character of the connection between the two bowls. Three stable diastereomers that interconvert through bowl inversions and central bond rotations were shown to exist.

25. David Angew Chem 2010

Ploshnik, E. ; Salant, A. ; Banin, U. ; Shenhar, R. Co-assembly of block copolymers and nanorods in ultrathin films: effects of copolymer size and nanorod filling fraction. Physical Chemistry Chemical Physics 2010, 12, 11885-11893.Abstract

Two-dimensional, hierarchical assemblies of nanorods were obtained by exploiting the structures afforded by block copolymers in ultrathin films. Under the appropriate conditions, the nanorods segregate to the film surface already upon casting the composite film, and organize with the block copolymer through phase separation. In this paper we compare the structures formed by CdSe nanorods of three different lengths and two polystyrene-block-poly(methyl methacrylate) copolymers with different nanorods/copolymer ratios, and study the temporal evolution of the structure in each case. It is found that the initial morphology of the film largely dictates the resulting structure. The combination of short nanorods and/or short copolymers is shown to be more prone to morphological defects, while assembling long nanorods with long copolymers leads to highly organized nanorod morphologies. These phenomena are explained by a combination of kinetic and thermodynamic factors.

24. Elina PCCP 2010

Daoulas, K. C. ; Cavallo, A. ; Shenhar, R. ; Mueller, M. Directed Assembly of Supramolecular Copolymers in Thin Films: Thermodynamic and Kinetic Advantages. Physical Review Letters 2010, 105, 108301.Abstract

Using computer simulation of a coarse-grained model for supramolecular polymers, we investigate the potential of quasiblock copolymers (QBCPs) assembled on chemically patterned substrates for creating device-oriented nanostructures. QBCPs are comprised of AB diblock copolymers and supramolecular B segments that can reversibly bond to any available B terminus, on either the copolymers or the B oligomers, creating a polydisperse blend of B homopolymers, and AB and ABA copolymers. We demonstrate the defect-free replication of patterns with perpendicularly crossing, A-preferential lines, where the same QBCP can simultaneously replicate patterns differing by up to 50% in their length scales. We demonstrate how the pattern affects the distribution of molecular architectures and the key role of supramolecular associations for replicating patterns with different length scales.

26. quasi-block copolymer on patterns - theory

Ploshnik, E. ; Salant, A. ; Banin, U. ; Shenhar, R. Hierarchical Surface Patterns of Nanorods Obtained by Co-Assembly with Block Copolymers in Ultrathin Films. Advanced Materials 2010, 22, 2774-2779.Abstract

Co-assembly of cadmium selenide nanorods in block copolymer films gives rise to anisotropic, hierarchical nanorod superstructures at the film surface. Unlike their observed behavior in the bulk composite, the nanorods preferentially orient perpendicular to the direction of the block copolymer domain, and the number of nanorods assembled across the domain is controlled by the ratio between the nanorod length and the domain width.

23. block copolymer-nanorod assembly 1

Eisenberg, D. ; Quimby, J. M. ; Jackson, E. A. ; Scott, L. T. ; Shenhar, R. Highly charged supramolecular oligomers based on the dimerization of corannulene tetraanion. Chemical Communications 2010, 46, 9010-9012.Abstract

The supramolecular dimerization of tetraanionic corannulene is utilized as a self-assembly motif for the construction of highly charged, buckybowl-based supramolecular oligomers. Oligomers of up to 7 units (3900 g mol(-1)) of reduced dicorannulenic monomers are identified and characterized by various NMR techniques, and the reversibility of their assembly is established through the concentration dependence of their molecular weight and the effect of monofunctional chain-stoppers.

27. David ChemComm 2010

Ben-Sasson, A. J. ; Avnon, E. ; Ploshnik, E. ; Globerman, O. ; Shenhar, R. ; Frey, G. L. ; Tessler, N. Patterned electrode vertical field effect transistor fabricated using block copolymer nanotemplates. Applied Physics Letters 2009, 95, 213301.Abstract

We report the design and implementation of a vertical organic field effect transistor which is compatible with standard device fabrication technology and is well described by a self consistent device model. The active semiconductor is a film of C(60) molecules, and the device operation is based on the architecture of the nanopatterned source electrode. The relatively high resolution fabrication process and maintaining the low-cost and simplicity associated with organic electronics, necessitates unconventional fabrication techniques such as soft lithography. Block copolymer self-assembled nanotemplates enable the production of conductive, gridlike metal electrode. The devices reported here exhibit On/Off ratio of 10(4).

20. patterned electrode for vertical FET

Daoulas, K. C. ; Cavallo, A. ; Shenhar, R. ; Mueller, M. Phase behaviour of quasi-block copolymers: A DFT-based Monte-Carlo study. Soft Matter 2009, 5 4499-4509.Abstract

We develop a mesoscopic density functional theory (DFT)-based Monte-Carlo approach for studying the phase behaviour of multi-component systems comprised of irreversibly bonded, conventional macromolecules and supramolecular entities. The latter can reversibly associate with each other and the conventional components to ``living'', equilibrium polymers. The computational approach can be applied to a broad class of supramolecular systems and we focus here on quasi-block copolymer systems that contain conventional, ``dead'' AB-copolymers with a supramolecular B-terminus and supramolecular B-units. The simulations show that, by properly selecting the architecture of the ``dead'' copolymers and by varying the supramolecular association constant and the incompatibility between the segment species, A and B, one obtains a variety of different microphase-separated morphologies and macrophase separations. Two representative phase diagrams are reported as a function of the association constant, E(b), and the Flory-Huggins parameter, chi, quantifying the repulsion between A and B segments. The simulation results are qualitatively rationalised by considering the dependence of the stoichiometry on the system's parameters, and fractionation effects between coexisting phases are illustrated.

19. quasi-block copolymer theory

Eisenberg, D. ; Filatov, A. S. ; Jackson, E. A. ; Rabinovitz, M. ; Petrukhina, M. A. ; Scott, L. T. ; Shenhar, R. Bicorannulenyl: Stereochemistry of a C40H18 biaryl composed of two chiral bowls. Journal of Organic Chemistry 2008, 73, 6073-6078.Abstract

The bicorannulenyl molecule is composed of two chiral bowls tethered by a single bond in a helical fashion. This simple combination of two chiral motifs gives rise to rich dynamic stereochemistry, where 12 conformers interconvert through bowl inversions and central bond rotation, and enantiomerizations occur via multistep processes. Interestingly, 8 out of 10 transition states are chiral, giving rise to mostly chiral enantiomerization pathways, where the molecule changes chirality without passing through an achiral conformation. However, analysis of the stereochemical landscape by DFT calculations and variable temperature NMR spectroscopy reveals that the energetically most favorable enantionterization pathway passes through one of the two achiral transition states. Single-crystal X-ray diffraction corroborates the DFT results and provides information on packing modes of bicorannulenyl molecules in the solid state that have not been seen previously for other buckybowls.

18. bicoannulenyl stereochemistry   JOC cover 2008

Kletenik-Edelman, O. ; Ploshnik, E. ; Salant, A. ; Shenhar, R. ; Banin, U. ; Rabani, E. Drying-mediated hierarchical self-assembly of nanoparticles: A dynamical coarse-grained approach. Journal of Physical Chemistry C 2008, 112, 4498-4506.Abstract

A coarse-grained lattice gas model is developed to study the drying-mediated self-assembly of nanoparticles on diblock copolymer substrates. The model describes the nanoparticles, the solvent and the diblock copolymer on length scales that are typical to the solvent bulk correlation length. Monte Carlo simulation techniques are used to delineate the various mechanisms of this out-of-equilibrium hierarchical self-assembly. Several different assembly scenarios corresponding to different selectivity of the nanoparticles/liquid/substrate are discussed. The role of surface tension, evaporation rate, diffusion rate, nanoparticle, coverage, and diblock copolymer periodicity is explored. Optimal conditions to form a stripe phase of nanoparticles along with predictions of novel 3D structures resulting from high nanoparticle and solvent selectivity are described.

16. Rabani JPCC 2008