Davidi, I. ; Shenhar, R. Synthesis of disk-shaped nanoparticle aggregates organized in hierarchical structures in block copolymer matrixes. Polymer 2015, 64, 39-45.Abstract

Disk-shaped nanoparticle aggregates organized in a hierarchical structure in a microphase separated block copolymer were prepared in a two-step process. First, a system comprising of polystyrene-block-poly(2-vinyl pyridine) and a palladium-pincer based surfactant was let to thermally equilibrate, resulting in the formation of structured material with hierarchically distributed concentrations of the palladium precursors. Then, in-situ reduction of the palladium precursors yielded the hierarchically organized nanocomposite. The importance of using an amphiphilic molecule for obtaining the hierarchical arrangement of the nanoparticle aggregates is demonstrated. Hierarchically arranged nanocomposites consisting of shape-controlled nanoparticle aggregates can potentially be useful as photonic materials with unique anisotropic optical response. (C) 2015 Elsevier Ltd. All rights reserved.

43. disk-shaped aggregates

Halevi, A. ; Halivni, S. ; Oded, M. ; Müller, A. H. E. ; Banin, U. ; Shenhar, R. Co-Assembly of A-B Diblock Copolymers with B'-type Nanoparticles in Thin Films: Effect of Copolymer Composition and Nanoparticle Shape. Macromolecules 2014, 47, 3022-3032.Abstract

The coassembly of A B diblock copolymers with B'-type nanoparticles (i.e., nanoparticles that are slightly incompatible with the B domain) leads to hierarchical structures, where the block copolymer phase separates first and the nanoparticles create close-packed arrays within the B domains due to a slower, secondary phase separation process. Here we report the results of a comprehensive study, which focused on two aspects: the influence of the nanoparticle shape (spherical vs rod-like) and the effect of the volume composition of the blocks. Three polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) copolymers featuring similar molecular weights but differing in PS volume fraction were mixed with spherical and rod-shaped poly(ethylene oxide)- (PEO-) capped CdS nanoparticles at different filling fractions and cast as thin films. Our results highlight the mutual influence between the block copolymer and the nanoparticles on the resulting morphology, demonstrating the ability to control the film morphology by the filling fraction of the nanoparticles and their tendency to localize at the film surface, and by confinement-induced nanoparticle aggregation. Most importantly, the results reveal the influence of the nanoparticle shape on the structure of the film.

41. co-assembly of B'-type nanorods in A-B block copolymers

This paper was highlighted in Advances in Engineering!

Davidi, I. ; Hermida-Merino, D. ; Keinan-Adamsky, K. ; Portale, G. ; Goobes, G. ; Shenhar, R. Dynamic Behavior of Supramolecular Comb Polymers Consisting of Poly(2-Vinyl Pyridine) and Palladium-Pincer Surfactants in the Solid State. Chemistry-A European Journal 2014, 20, 6951-6959.Abstract

When poly(2-vinyl pyridine) is combined with Pd-pincer-based organometallic surfactants, a mesomorphic structure forms due to weak stacking interactions between the pyridine units and the Pd-pincer headgroups. The weak binding between the surfactant and the polymer competes with the tendency of the aliphatic tails of the surfactant to crystallize. Here, we demonstrate that over extended periods of incubation, the crystallization tendency of the surfactant tails causes the surfactant molecules to detach from the polymer and gives rise to additional packing modes of the alkyl tails featuring higher crystalline order. The dynamic behavior of these aged structures was investigated by variable-temperature small-angle X-ray scattering (SAXS) and solid-state 13CNMR, and revealed the influence of thermal changes on the molecular level, and how these changes propagate to the mesoscale structure.

40. dynamic behavior of pi-stacked amphiphile-block copolymer system

Davidi, I. ; Patra, D. ; Herrnida-Merino, D. ; Portale, G. ; Rotello, V. M. ; Raviv, U. ; Shenhar, R. Hierarchical Structures of Polystyrene-block-poly(2-vinylpyridine)/Palladium-Pincer Surfactants: Effect of Weak Surfactant-Polymer Interactions on the Morphological Behavior. Macromolecules 2014, 47, 5774-5783.Abstract

Selective segregation of surfactant molecules to one domain type of block copolymers in the melt leads to the formation of hierarchical structures. Here we show that combining an organometallic, Pd-pincer-based surfactant (Pd-SCS) with a polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer leads to hierarchical structures due to weak stacking interactions between the Pd-pincer complex and the pyridine units. These structures feature a different morphological behavior than analogous systems, including the formation of perforated lamellae (PL) over a wide range of surfactant filling fractions and a distinct swelling anisotropy behavior of the copolymer chains by the added surfactant molecules. The results suggest that the strength of interaction between the surfactant and the compatible block influences the degree of segregation between the blocks. This study lays the foundations for the creation of organized, hierarchical arrays of inorganic nanoclusters that are periodic on two different length scales.

42. hierarchical structures of Pd-pincer-block copolymer system

Eisenberg, D. ; Quimby, J. M. ; Scott, L. T. ; Shenhar, R. 1,3,5-tricorannulenylbenzene: stereochemistry, reduction and supramolecular dimerization of a branched oligocorannulene. Journal of Physical Organic Chemistry 2013, 26, 124-130.Abstract

Oligocorannulenes are polyarenes composed of several corannulene units that are covalently linked. Their behavior arises both from the diverse properties of each corannulenyl unit and from the interactions between them. In this paper, we present the synthesis, stereochemistry, reduction, and self-assembly properties of a novel type of oligocorannulene: branched 1,3,5-tricorannulenylbenzene. Several stereodynamical elements combine to give rich stereochemistry: bowl-to-bowl inversion, rotation about the aryl-aryl single bonds, and residual stereoisomerism of molecular propellers. Reduction with lithium metal yields an intermediate hexaanion and ultimately produces a highly charged dodecaanion. Self-diffusion NMR demonstrates that the dodecaanion undergoes supramolecular dimerization through charged polyarene stacking, wherein two molecules are linked at all three contact points. The preference for dimerization over dendrimerization is attributed to an entropic effect. The dimer is found to undergo complex structural dynamics, as well as ion-pairing dynamics, as revealed by variable-temperature 1H- and 7Li-NMR. Copyright (C) 2012 John Wiley & Sons, Ltd.

35. tricorannulenyl benzene anions

Liedel, C. ; Pester, C. W. ; Ruppel, M. ; Lewin, C. ; Pavan, M. J. ; Urban, V. S. ; Shenhar, R. ; Bösecke, P. ; Böker, A. Block Copolymer Nanocomposites in Electric Fields: Kinetics of Alignment. ACS Macro Letters 2013, 2 53-58.Abstract

We investigate the kinetics of block copolymer/nanoparticle composite alignment in an electric field using in situ transmission small-angle X-ray scattering. As a model system, we employ a lamellae forming polystyrene-block-poly(2-vinyl pyridine) block copolymer with different contents of gold nanoparticles in thick films under solvent vapor annealing. While the alignment improves with increasing nanoparticle fraction, the kinetics slows down. This is explained by changes in the degree of phase separation and viscosity. Our findings provide extended insights into the basics of nanocomposite alignment.

36. kinetics of nanocomposite alignment under E-field

Pavan, M. J. ; Shenhar, R. Effect of Channel Confinement on the Coarsening Kinetics of Nanoparticles Deposited on Semicrystalline Polymer Templates. ChemPlusChem 2013, 78, 1015-1023.Abstract

Dodecanethiol-capped gold nanoparticles (NPs) deposited onto a poly(ethylene glycol) substrate quickly coarsen over a timescale of days when stored under ambient conditions. The NP coarsening was studied at different surface coverages and temperatures. The coarsening of NPs depended on their location on the film; NPs located inside the channels coarsened in a different fashion than NPs deposited on the plateaus. Size distributions studied by image analysis and comparison to theoretical distribution functions shed light on the coarsening mechanism in each case, revealing the role of dimensionality.

39. effect of channel confinement

This paper was highlighted in Chemistry Views!

Liedel, C. ; Schindler, K. A. ; Pavan, M. J. ; Lewin, C. ; Pester, C. W. ; Ruppel, M. ; Urban, V. S. ; Shenhar, R. ; Böker, A. Electric-Field-Induced Alignment of Block Copolymer/Nanoparticle Blends. Small 2013, 9 3276-3281.Abstract

External electric fields readily align birefringent block-copolymer mesophases. In this study the effect of gold nanoparticles on the electric-field-induced alignment of a lamellae-forming polystyrene-block-poly(2-vinylpyridine) copolymer is assessed. Nanoparticles are homogeneously dispersed in the styrenic phase and promote the quantitative alignment of lamellar domains by substantially lowering the critical field strength above which alignment proceeds. The results suggest that the electric-field-assisted alignment of nanostructured block copolymer/nanoparticle composites may offer a simple way to greatly mitigate structural and orientational defects of such films under benign experimental conditions.

37. E-field induced alignment of nanocomposites

Ploshnik, E. ; Langner, K. M. ; Halevi, A. ; Ben-Lulu, M. ; Müller, A. H. E. ; Fraaije, J. G. E. M. ; Agur Sevink, G. J. ; Shenhar, R. Hierarchical Structuring in Block Copolymer Nanocomposites through Two Phase-Separation Processes Operating on Different Time Scales. Advanced Functional Materials 2013, 23, 4215-4226.Abstract

Tailoring the size and surface chemistry of nanoparticles allows one to control their position in a block copolymer, but this is usually limited to one-dimensional distribution across domains. Here, the hierarchical assembly of poly(ethylene oxide)-stabilized gold nanoparticles (Au-PEO) into hexagonally packed clusters inside mesostructured ultrathin films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is described. A close examination of the structural evolution at different nanoparticle filling fractions and PEO ligand molecular weights suggests that the mechanism leading to this structure-within-structure is the existence of two phase separation processes operating on different time scales. The length of the PEO ligand is shown to influence not only the interparticle distances but also the phase separation processes. These conclusions are supported by novel mesoscopic simulations, which provide additional insight into the kinetic and thermodynamic factors that are responsible for this behavior.

38. co-assembly of B'-nanoparticles with A-B block copolymers

Davidi, I. ; Semionov, A. ; Eisenberg, D. ; Goobes, G. ; Shenhar, R. Mesomorphic behavior induced by stacking interactions between poly(2-vinyl pyridine) and palladium pincer surfactants in the solid state. Soft Matter 2012, 8 7393-7401.Abstract

Combining poly(2-vinyl pyridine) (P2VP) with organometallic surfactants based on a Pd-SCS pincer complex in the solid state leads to the formation of mesomorphic structures even with the lack of coordinative bonding between the pyridine groups and the surfactant molecules. Through a combination of spectroscopic methods and quantum chemical calculations we reveal that the interaction responsible for the formation of the supramolecular, comb polymer architectures leading to these mesomorphic structures is a dipolar stacking interaction between the Pd-C bond of the surfactant and the pyridine ring of the polymer. This conclusion is further supported by comparison to a system where coordinative binding between the surfactant and the polymer was induced. Additional DSC analysis shows that, unlike the system featuring coordinative binding, the weak binding to the polymer through dipolar stacking facilitates the crystallization of the alkyl residues. Such organized assemblies of metal precursors can serve for the creation of hybrid materials and organized nanocomposites.

32. Inbal Soft Matter 2012

Pavan, M. J. ; Ploshnik, E. ; Shenhar, R. Nanoparticle Assembly on Topographical Polymer Templates: Effects of Spin Rate, Nanoparticle Size, Ligand, and Concentration. Journal of Physical Chemistry B 2012, 116, 13922-13931.Abstract

The ability to assertible nanoparticles (NPs) into desired patterns. in a controlled fashion is crucial for the study. of collective properties and for the fabrication of a variety of devices. Drying mediated assembly directed by a template provides a facile route for organizing NPs in predefined patterns. We utilize the. branched topographical landscapes displayed by partially crystallized poly(ethylene glycol) (PEG) films as a generic template for studying. the drying mediated organization of dodecanethiol- and polystyrene thiol-protected gold NPs (Au-DT and Au-PS), and explore the combined effects of NP size and ligand, concentration, and spin rate on the distribution. of NPs inside the channels. We Show how NP concentration and the spin rate applied during NP deposition can be used to influence the tendency of NPs either to fill channel uniformly or to localize near the channel edges, explain the important role of the enhanced aggregation tendency of larger NPs on the resulting morphologies, and demonstrate how this tendency can be tuned by the proper choice Of ligands. The different effects are explained in the context of possible scenarios of drying mediated assembly by analyzing the relevant interactions and forces acting on the NPs during solvent evaporation.

34. nanoparticle assembly on PEG 2

Eisenberg, D. ; Shenhar, R. Polyarene anions: interplay between theory and experiment. Wiley Interdisciplinary Reviews-Computational Molecular Science 2012, 2 525-547.Abstract

Polyarenes, or polycyclic aromatic hydrocarbons (PAHs), represent a ubiquitous and heavily studied type of compounds, appealing for their interesting spectroscopic, supramolecular, organometallic, and other properties. A major branch of research is concerned with polyarene anions: their electronic and structural properties, reactivity, aromaticity, and spectroscopy. This review describes the major role of computational investigations in complementing, explaining, and guiding experimental research, and thus providing invaluable contribution to our understanding of polyarene anions. The scope of this review focuses on polyarenes composed only from sp(2)-hybridized carbons and limits the discussion to the quantum-mechanical method of calculation. The topics covered include computation-assisted characterization; choice of methods; transformations induced by reduction, including anistropic charge redistributions, reorganization of bonding structure, flattening of curved polyarenes (buckybowls), and Jahn-Teller distortion; aromaticity topics such as ring currents and aromaticity measures; reactivity, for example, toward electrophilic substitution or ring closure, acidity and basicity, and self-assembly interactions in solution and in the gas phase; and finally, spectroscopy, mainly for astrochemical research, ranging from the mid-infrared to the far-ultraviolet spectral ranges. (C) 2011 John Wiley & Sons, Ltd.

31. polyarene anions review

Eisenberg, D. ; Quimby, J. M. ; Ho, D. ; Lavi, R. ; Benisvy, L. ; Scott, L. T. ; Shenhar, R. Special Electronic Structure and Extended Supramolecular Oligomerization of Anionic 1,4-Dicorannulenylbenzene. European Journal of Organic Chemistry 2012, 6321-6327.Abstract

The chemistry of oligocorannulenes (compounds composed of two or more corannulenyl moieties) arises from the properties of each corannulenyl and from the interactions between them. Varying the linkage between the corannulenyl moieties can influence the interaction and give rise to new properties in these carbon-rich compounds. This work describes the synthesis and reduction of 1,4-dicorannulenylbenzene in which a rigid aromatic benzene spacer leads to new electronic and supramolecular behavior, as shown by NMR, EPR, and UV/Vis spectroscopy, as well as DFT calculations. Structural and energy analyses of the dianion revealed that the benzene ring modifies the electronic communication between the two bowls. To preserve the aromatic character of the benzene, conjugation between the bowls is minimized and the benzene assumes a biradical bonding pattern rather than a quinoidal one. At the octaanionic stage, self-diffusion NMR experiments revealed extended supramolecular polymerization through charged polyarene stacking. The highly charged supramolecular oligomers are composed of up to 11 monomers per chain, significantly longer than the first (bicorannulenyl) oligomers of this type. This observation constitutes a proof-of-principle for controlling this novel type of polymer through modification of the intercorannulenyl spacer.

33. dicorannulenyl benzene electronic structure   European Journal of Organic Chemistry 2012

Avnon, E. ; Yaacobi-Gross, N. ; Ploshnik, E. ; Shenhar, R. ; Tessler, N. Low cost, nanometer scale nanoimprinting - Application to organic solar cells optimization. Organic Electronics 2011, 12, 1241-1246.Abstract

We show that nanoimprinting can be robust and reliable enough to be compatible with device optimization procedure. This is enabled by a method for producing nanoimprint master stamps using block copolymer lithography. This method is not only robust and low cost but it also allows patterning with nanometer size features over centimeter scale area. The large number of stamps easily produced in parallel are used to fabricate organic solar cells with controlled interpenetrating heterojunction. The power conversion efficiency is shown to increase with the pattern depth reaching a two fold increase for only similar to 35 nm deep pattern. (C) 2011 Elsevier B.V. All rights reserved.

29. imprinting for solar cells

Weiss, E. ; Daoulas, K. C. ; Mueller, M. ; Shenhar, R. Quasi-Block Copolymers: Design, Synthesis, and Evidence for Their Formation in Solution and in the Melt. Macromolecules 2011, 44, 9773-9781.Abstract

A family of block copolymers featuring dynamically controlled compositions is presented. These copolymers, termed ``quasi-block copolymers'' (q-BCP), consist of a supramolecular polymer as one of the blocks. A conventional polymer end-capped with a functionality that is complementary to the supramolecular monomer is used to terminate the supramolecular block, giving rise to a block copolymer architecture. In this work we have utilized N,N'-2,4-bis((2-ethylhexyl)ureido)toluene (EHUT) as the supramolecular monomer and employed two types of modified 2,4-bis(ureido)toluene polystyrenes as the end-functionalized conventional polymer. Solution viscosity measurements with different solvent compositions and DSC analysis of poly(EHUT)/functionalized-PS blends provide compelling evidence for the formation of self-assembled q-BCP structures both in solution and in the melt. The qualitative role of chain stoppers on the molecular weight distribution is studied by simulations.

30. quasi-block copolymers

Pavan, M. J. ; Shenhar, R. Two-dimensional nanoparticle organization using block copolymer thin films as templates. Journal of Materials Chemistry 2011, 21, 2028-2040.Abstract

The creation of ordered nanoparticle assemblies is one of the main prerequisites for the utilization of nanoparticles in advanced device applications. However, while considerable progress has been made in the precision synthesis of high quality, uniform nanoparticles of different compositions, sizes and shapes, our ability to organize them into ordered structures still faces major challenges. This Feature Article focuses on a facile approach developed in recent years for the fabrication of two-dimensionally organized nanoparticle assemblies, which is based on patterning as a simple and straightforward assembly mechanism and on block copolymer films as easily created templates.

28. Mariela JMC 2011

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