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Eugene R Zubarev

Publications and source records attributed to Eugene R Zubarev.

13 recordsLinked to original sources
PubMed2006

Amphiphilicity-driven organization of nanoparticles into discrete assemblies.

We present a method for organizing metallic nanoparticles in solution that is based on the hydrophobic effect and does not require either hydrogen bonding or molecular recognition. When amphiphilic V-shaped molecules are attached to a gold cluster, an aggregation process ensues in aqueous solution and leads to the formation of well-defined cylindrical and vesicular nanoarrays of particles. The metallic clusters densely pack at the boundary separating the hydrophobic core from the hydrophilic corona of the hybrid micelle-like aggregates. This design allows one to assemble and disassemble the nanoparticles in a reversible manner and control the size and the morphology of the arrays by changing the conditions of the solution preparation. The versatility of this method is demonstrated by its applicability to different metals with covalently attached amphiphilic arms with various chemical compositions (PS-PEO and PB-PEO) and molecular weights.

Journal Article↗
PubMed2006

The molecular basis of self-assembly of dendron-rod-coils into one-dimensional nanostructures.

We describe here a comprehensive study of solution and solid-state properties of self-assembling triblock molecules composed of a hydrophilic dendron covalently linked to an aromatic rigid rod segment, which is in turn connected to a hydrophobic flexible coil. These dendron-rod-coil (DRC) molecules form well-defined supramolecular structures that possess a ribbonlike morphology as revealed by transmission-electron and atomic-force microscopy. In a large variety of aprotic solvents, the DRC ribbons create stable networks that form gels at concentrations as low as 0.2% by weight DRC. The gels are thermally irreversible and do not melt at elevated temperatures, indicating high stability as a result of strong noncovalent interactions among DRC molecules. NMR experiments show that the strong interactions leading to aggregation involve mainly the dendron and rodlike blocks, whereas oligoisoprene coil segments remain solvated after gelation. Small-angle X-ray scattering (SAXS) profiles of different DRC molecules demonstrate an excellent correlation between the degree-of-order in the solid-state and the stability of gels. Studies on two series of analogous molecules suggest that self-assembly is very sensitive to subtle structural changes and requires the presence of at least four hydroxyl groups in the dendron, two biphenyl units in the rod, and a coil segment with a size comparable to that of the rodlike block. A detailed analysis of crystal structures of model compounds revealed the formation of stable one-dimensional structures that involve two types of noncovalent interactions, aromatic pi-pi stacking and hydrogen bonding. Most importantly, the crystal structure of the rod-dendron compound shows that hydrogen bonding not only drives the formation of head-to-head cyclic structures, but also generates multiple linkages between them along the stacking direction. The cyclic structures are tetrameric in nature and stack into ribbonlike objects. We believe that DRC molecules utilize the same arrangement of hydrogen bonds and stacking of aromatic blocks observed in the crystals, explaining the exceptional stability of the nanostructures in extremely dilute solutions as well the thermal stability of the gels they form. This study provides mechanistic insights on self-assembly of triblock molecules, and unveils general strategies to create well-defined one-dimensional supramolecular objects.

Anthracenes↗
PubMed2006

Langmuir-Blodgett monolayers of gold nanoparticles with amphiphilic shells from V-shaped binary polymer arms.

Gold nanoparticles functionalized with amphiphilic polybutadiene-poly(ethylene glycol) (PB-PEG) V-shaped arms formed stable Langmuir monolayers at the air-water and the air-solid interfaces. At these interfaces, the binary arms vertically segregated into a dense polymer corona, which surrounded the gold nanoparticles, preventing their large-scale agglomeration and keeping individual nanoparticles well-separated from each other and forming flattened, pancake nanostructures. The presence of both PEG and PB chains in the close proximity to the gold core was confirmed by surface enhanced Raman spectroscopy, whereas the AFM phase contrast images revealed the presence of 2 nm gold cores surrounded by the polymer shell with the diameter of 11 nm. We suggest that the amphiphilic shell drives their spontaneous organization into discrete 2D pancake-like hybrid structures that measured up to 10 microm in diameter and had a high packing density of gold clusters.

Journal Article↗
PubMed2006

Amphiphilic gold nanoparticles with V-shaped arms.

Here we describe a very efficient method to produce well-defined amphiphilic gold nanoparticles (Au NPs) with an equal number of hydrophobic and hydrophilic arms which are distributed along the surface of a 2-nm gold core in an alternating fashion. The strategy involves direct coupling of V-shaped block copolymer amphiphile 2 with a carboxylic group at its junction point to mercaptophenol-terminated Au NPs. The reaction proceeds under mild esterification conditions and yields the product with a molecular weight of 40 kDa, high grafting density (2.9 chains/nm2), and extremely low polydispersity (1.07). The big advantage of this approach is the opportunity to avoid the use of expensive and often inaccessible polymeric thiols. The method described here is applicable to any carboxyl-terminated molecules and can be used for the preparation of complex, yet well-defined, macromolecular hybrid structures such as 1 (Au(PB-PEG)n). The new product, which was characterized by a combination of SEC, NMR, UV-vis, DLS, and TEM, represents a unique example of gold nanoparticles soluble in any conventional solvent.

Journal Article↗
PubMed2006

From small building blocks to complex molecular architecture.

[reaction: see text] We describe a synthesis of a dendrimer-like amphiphile containing a flat rigid core and 12 hydrophobic and hydrophilic arms. We employ a modular approach based on stepwise protection chemistry starting from simple building blocks. The key feature of this approach is the absence of a polymerization step, which makes it applicable for linear monofunctionalized precursors of any kind. This strategy also allows for precise control of the number of arms and ensures their alternating arrangement.

Journal Article↗
PubMed2005

In-situ observation of switchable nanoscale topography for y-shaped binary brushes in fluids.

Direct, in-fluid observation of the surface morphology and nanomechanical properties of the mixed brushes composed of Y-shaped binary molecules PS-PAA revealed nanoscale network-like surface topography formed by coexisting stretched soluble PAA arms and collapsed insoluble PS chains in water. Placement of Y-shaped brushes in different fluids resulted in dramatic reorganization ranging from soft repellent layer covered by swollen PS arms in toluene to an adhesive, mixed layer composed of coexisting swollen PAA and collapsed PS arms in water. These binary layers with the overall nanoscale thickness can serve as adaptive nanocoatings with stimuli-responsive properties.

Acrylic Resins↗
PubMed2004

Interfacial micellar structures from novel amphiphilic star polymers.

An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic/hydrophilic arms of polystyrene (PS) and poly(acrylic acid) (PAA) connected to a well-defined rigid aromatic core was studied at the air-water and the air-solid interfaces. At the air-water interface, the molecules spontaneously form pancakelike micellar aggregates which measure up to several microns in diameter and 5 nm in thickness. Upon reduction of the surface area per molecule to 7 nm2, the two-dimensional micelles merged into a dense monolayer. We suggest that confined phase separation of dissimilar polymer arms occurred upon their segregation on the opposite sides of the rigid disklike aromatic core, forcing the rigid cores to adopt a face-on orientation with respect to the interface. Upon transfer onto solid supports the PS chains face the air-film interface making it completely hydrophobic, and the PAA chains were found to collapse and form a thin flattened underlayer. This study points toward new strategies to create large 2D microstructures with facial amphiphilicity and suggests a profound influence of star molecular architecture on the self-assembly of amphiphiles at the air-water interface.

Acrylic Resins↗
PubMed2003

Y-shaped amphiphilic brushes with switchable micellar surface structures.

We observed novel nanoscale surface structures of segregated pinned micelles and craterlike micelles formed by grafted Y-shaped molecules and their reversible reorganization in selective solvents. The Y-shaped molecules have two incompatible polymer chains (polystyrene and poly(tert-butyl acrylate)) attached to a functional stemlike segment capable of covalent grafting to a functionalized silicon surface. Postgrafting hydrolysis of poly(tert-butyl acrylate) arms imparts amphiphilicity to the brush. We demonstrated that spatial constraints induced by a chemical junction of two relatively short (6-10 nm) dissimilar arms in such Y-shaped molecules lead to the formation of segregated micellar surface nanostructures in the grafted layer. We proposed a model of these segregated pinned micelles and the corresponding reverse micelles (craterlike structures) featuring different segregation states of hydrophobic polystyrene and hydrophilic poly(acrylic acid) arms. The arms undergo conformational rearrangements in selective solvents in a controlled and reversible fashion. These nanoscale structural reorganizations define adaptive macroscopic wetting surface properties of the amphiphilic Y-shaped brushes. This surface structure and switchable behavior can be considered as a promising way toward the patterning of solid substrates with adaptive nanowells, which could be used for trapping of adsorbing nanoscale objects.

Journal Article↗
PubMed2003

Synthesis and self-assembly of a heteroarm star amphiphile with 12 alternating arms and a well-defined core.

We report on a stepwise synthesis of a heteroarm starlike amphiphile containing 12 alternating arms (six polystyrene and six poly(acrylic acid)) connected to a hexabiphenyl aromatic core. The synthesis does not involve polymerization, and only commercially available precursors are used. Most importantly, this amphiphile undergoes self-assembly into spherical and wormlike cylindrical micelles in aqueous and methanol solutions, and forms reverse 1D micellar structures in chloroform. This remarkable morphological diversity of the reported amphiphile 1 is believed to be a direct consequence of its well-defined molecular architecture.

Journal Article↗
PubMed2003

Assembling a lasing hybrid material with supramolecular polymers and nanocrystals.

The combination of bottom-up and top-down processes to organize nanophases in hybrid materials is a key strategy to create functional materials. We found that oxide and sulphide nanocrystals become spontaneously dispersed in organic media during the self-assembly of nanoribbon supramolecular polymers. These nanoribbon polymers form by self-assembly of dendron rodcoil molecules, which contain three molecular blocks with dendritic, rod-like, and coil-like architectures. In an electric field these supramolecular assemblies carrying bound nanocrystals migrate to the positive electrode in an etched channel and align in the field. In the system containing ZnO nanocrystals as the inorganic component, both phases are oriented in the hybrid material forming an ultraviolet lasing medium with a lower threshold relative to pure ZnO nanocrystals.

Crystallization↗
PubMed2002

Dendron rodcoils: synthesis of novel organic hybrid structures.

Convergent and divergent syntheses of novel organic hybrid structures termed dendron rodcoils (DRC) containing dendritic, rodlike, and coillike segments are described. The aryl ester dendron masked with 32 trifluoromethyl groups is prepared via a convergent approach using 5-(tert-butyldimethylsiloxy)isophthalic acid as the monomer unit. The activation of the focal point of the dendron allows for successful coupling between the dendron and the diblock rodcoil molecules synthesized separately. In another example, the dendritic block is grown via divergent strategy from the terminus of rodcoil using 3,5-bis(tert-butyldimethylsiloxy)benzoic acid as an AB(2) monomer. A combination of catalyzed esterification reactions and silyl deprotection chemistry proved to be a very efficient method for construction of these nanosized structures with unusual molecular architecture. Both synthetic strategies allowed for the preparation of DRCs with nearly monodisperse dendritic blocks as demonstrated by NMR, MALDI-TOF, and GPC measurements.

Journal Article↗