Oren Regev - Profile on Academia.edu (original) (raw)

Papers by Oren Regev

Zeolites, 1994

The microstructural evolution in the nucleation stage of a synthesis reaction of ZSM-5 zeolite wa... more The microstructural evolution in the nucleation stage of a synthesis reaction of ZSM-5 zeolite was studied, with particular emphasis on the role of the organic cation, TPA + (tetrapropylammonium).. Direct observation of the microstructure was achieved by cryo-transmission electron microscopy (cryo-TEM). The quantitative evaluation of the structural units was obtained by small-angle X-ray scattering (SAXS) measurements. In the presence of the organic cation TPA ÷, we found globular structural units 5 nm in diameter that aggregate to elongated bodies 44 nm long. The globular structural units were found in reaction mixtures with or without the organic template TPA-OH, as long as the pH of the initial solution was kept above 11.6. Without TPA ÷, aggregation to cylindrical particles was not observed after 2 h of heating, and no ZSM-5 crystallinity was attained at the end of the reaction (after 8 d). These results suggest that the zeolite ZSM-5 building blocks are globular structural units, 5 nm in diameter, containing silica, alumina, organic cation, and water, which fuse together to produce elongated aggregates that may compose the final unit cell. It is concluded that the globular structural unit is a cluster of tetrapods similar to those found in the final ZSM-5 crystals.

Enhancing the immunogenicity of liposomal hepatitis B surface antigen (HBsAg) by controlling its delivery from polymeric microspheres

Journal of Pharmaceutical Sciences, 2000

Microencapsulated liposome systems (MELs) were investigated as a potential immunization carrier f... more Microencapsulated liposome systems (MELs) were investigated as a potential immunization carrier for a recombinant 22-nm hepatitis B surface antigen (HBsAg) particle. MELs were prepared by first entrapping the HBsAg particles within liposomes composed of phosphatidylcholine:cholesterol (1:1 molar ratio), which were then encapsulated within alginate-poly(L-lysine) (PLL) hydrogel microspheres. The entrapped HBsAg particles retained immunoreactivity, as judged by an enzyme-linked immunosorbent assay (ELISA). Direct imaging of HBsAg particles and HBsAg incorporated into liposomes by cryo-transmission electron microscopy (cryo-TEM) indicated that HBsAg is embedded in the liposomal membrane. The antigenic particles were released from MELs mainly within the context of liposomes. The release rates in vitro and in vivo depended on the molecular weight of PLL used for MEL coating; MELs-214, coated with 214 kDa PLL, released the liposomal HBsAg at much higher rates than MELs-25, which was coated with 25 kDa PLL. Concomitantly, the specific anti-HBsAg titers in mice receiving HBsAg in MELs-214 were higher than those induced by MELs-25. MELs-214 were more efficient than conventional liposomes or alum in eliciting higher and prolonged antibody levels in mice. The ability of MELs to provide an HBsAg depot as well as a sustained release of liposomal HBsAg suggests that these carriers may be an ideal immunoadjuvant.

Directing Silver Nanoparticles into Colloid−Surfactant Lyotropic Lamellar Systems

Journal of Physical Chemistry B, 1999

... Wei Wang, † Shlomo Efrima,* † and Oren Regev ‡. Departments ... respectively. The structural ... more ... Wei Wang, † Shlomo Efrima,* † and Oren Regev ‡. Departments ... respectively. The structural characteristics of the phase can be derived from SAXS, as the position (q max ) of the firstBragg peak is related to the lamellar spacing, d l = 2π/q max . ...

Directing Oleate Stabilized Nanosized Silver Colloids into Organic Phases

Langmuir, 1998

Nanosized hydrophobic, oleate stabilized silver organosols in various organic solvents are obtain... more Nanosized hydrophobic, oleate stabilized silver organosols in various organic solvents are obtained using a solvent exchange method. The silver particles are initially prepared as a hydrosol in the presence of sodium oleate (surfactant). Then a transfer of the colloid to an ...

Characterization of graphene-nanoplatelets structure via thermogravimetry

Analytical Chemistry, 2015

The rapid increase in graphene-based applications has been accompanied by novel top-down manufact... more The rapid increase in graphene-based applications has been accompanied by novel top-down manufacturing methods for graphene and its derivatives (e.g., graphene nanoplatelets (GnPs)). The characterization of the bulk properties of these materials by imaging and surface techniques (e.g., electron microscopy and Raman spectroscopy) is only possible through laborious and time-consuming statistical analysis, which precludes simple and efficient quality control during GnP production. We report that thermogravimetry (TG) may be utilized, beyond its conventional applications (e.g., quantification of impurities or surfactants, or labile functional groups) to characterize bulk GnP properties. We characterize the structural parameters of GnP (i.e., defect density, mean lateral dimension, and polydispersity) by imaging and surface techniques, on one hand, and by a systematic TG, on the other. The combined data demonstrate that the combustion temperature of commercially available and laboratory-prepared GnPs is correlated with their mean lateral dimension and defect density, while the combustion temperature range is proportional to their polydispersity index. Mapping all these parameters allows one to evaluate the GnPs&amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; structure following a simple thermogravimetric experiment (without necessitating further statistical analysis). Finally, TG is also used to detect and quantify different GnP constituents in powder and to conduct rapid quality-control tests during GnP production.

The ␤-lactoglobulin (␤-LG) protein was discovered to be an efficient and selective dispersant for... more The ␤-lactoglobulin (␤-LG) protein was discovered to be an efficient and selective dispersant for carbon nanotubes (CTNs) with certain diameters. A dispersion process of CTNs by the ␤-LG was studied, focusing on the relationships between the surface curvature of the CNT and the ␤-LG's efficiency in dispersing them, using cryogenic-transmission electron microscopy (cryo-TEM) and optical spectroscopy. Plausible binding sites of the ␤-LG, responsible for the interaction of the protein with CNTs of various diameters (surface curvatures) were also investigated and were found to be in good agreement with corresponding docking calculations.

High aspect ratio (>1000) CdS nanostructures were prepared via ultrasound treatment of parent nan... more High aspect ratio (>1000) CdS nanostructures were prepared via ultrasound treatment of parent nanowires (NWs) dispersed in sodium dodecyl sulfate (SDS) aqueous solution. The CdS parent NWs were prepared using ordered mesoporous silica, SBA-15, as a template. The elongated nanostructures (ENS), namely, NWs, nanoribbons and nanotubes, form stable dispersions in aqueous solutions. Electron microscopy and X-ray diffraction techniques were used to characterize both the parent NWs and the ENS. While the structure of the parent NWs is crystalline cubic, the ENS are amorphous. We show that the amorphous ENS bud from the parent bundled NWs. Ultrasound power and duration, presence of commensurate surfactant and calcination temperature of the templating SBA-15 are critical parameters in the formation of ENS in aqueous solution.

Templating nanostructures by mesoporous materials with an emphasis on room temperature and cryogenic TEM studies

Current Opinion in Colloid & Interface Science, 2005

Rapid strides realized in the field of ordered mesoporous silica (OMS) with a well-defined pore s... more Rapid strides realized in the field of ordered mesoporous silica (OMS) with a well-defined pore shape and nanometric sizes, provide new gateways for the preparation of nanostructured materials having controlled shape and size with a very narrow distribution. The focus of the current review is on the synthesis of nanostructures templated by OMS either in bulk or in thin film

Shape Changes of C 16 TABr Micelles on Benzene Solubilization

The Journal of Physical Chemistry B, 1999

... Niklas Hedin, Ruslan Sitnikov, István Furó,* Ulf Henriksson, and Oren Regev . Divisi... more ... Niklas Hedin, Ruslan Sitnikov, István Furó,* Ulf Henriksson, and Oren Regev . Division of Physical Chemistry, Department of Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden, and Department ...

Talanta, 2008

Biological sensing is explored through novel stable colloidal dispersions of pyrrole-benzophenone... more Biological sensing is explored through novel stable colloidal dispersions of pyrrole-benzophenone and pyrrole copolymerized silica (PPy-SiO 2 -PPyBPh) nanocomposites, which allow covalent linking of biological molecules through light mediation. The mechanism of nanocomposite attachment to a model protein is studied by gold labeled cholera toxin B (CTB) to enhance the contrast in electron microscopy imaging. The biological test itself is carried out without gold labeling, i.e., using CTB only. The protein is shown to be covalently bound through the benzophenone groups. When the reactive PPy-SiO 2 -PPyBPh-CTB nanocomposite is exposed to specific recognition anti-CTB immunoglobulins, a qualitative visual agglutination assay occurs spontaneously, producing as a positive test, PPy-SiO 2 -PPyBPh-CTB-anti-CTB, in less than 1 h, while the control solution of the PPy-SiO 2 -PPyBPh-CTB alone remained well-dispersed during the same period. These dispersions were characterized by cryogenic transmission microscopy (cryo-TEM), scanning electron microscopy (SEM), FTIR and X-ray photoelectron spectroscopy (XPS).

Small, 2008

The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfact... more The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions is investigated at room temperature. Smallangle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) are used for characterization of bulk dispersions and nanometrically thin films. Additional carbonaceous additives (fullerenes, multi-walled carbon nanotubes, and carbon black) serve as reference systems. It is found that dispersions of carbonaceous additive (excluding fullerenes) at intermediate surfactant concentrations (below the liquid-crystalline region of the native surfactant) induce demixing and macroscopic phase separation in otherwise homogeneous solutions of CTAB. Two coexisting liquid phases of similar CTAB concentrations are observed, with the carbonaceous species residing within the lower phase. At high CTAB concentrations (liquid-crystal region) the SWNTs are found to incorporate into the ordered lyotropic liquid-crystalline phase while preserving the native d-spacing. Investigation of nanometrically thin films at intermediate surfactant concentrations under external shear reveals shear-induced structure (SIS) in the presence of minute amounts of SWNTs. The effect is found to be exclusive to SWNT and does not occur in dispersions of other carbonaceous additives.

Nano Letters, 2002

Single-wall carbon nanotubes pack into crystalline ropes that aggregate into tangled networks due... more Single-wall carbon nanotubes pack into crystalline ropes that aggregate into tangled networks due to strong van der Waals attraction. Aggregation acts as an obstacle to most applications, and diminishes the special properties of the individual tubes. We describe a simple procedure for dispersing as-produced nanotubes powder in aqueous solutions of Gum Arabic. In a single step, a stable dispersion of full-length, well separated, individual tubes is formed, apparently due to physical adsorption of the polymer.

Microporous and Mesoporous Materials, 2000

A novel family of mesoporous molecular sieves (M41-S) has recently been reported by scientists of... more A novel family of mesoporous molecular sieves (M41-S) has recently been reported by scientists of Mobil Oil Research and Development. During its synthesis a base-or acid-catalyzed polymerization of inorganic compounds (silica in most cases) takes place around surfactant micelles that serve as a templating agent. At the end of the synthesis, a silica matrix imbedded by micelles, namely, a mesoporous material, is obtained. Its mechanism of formation is not yet completely understood. We have studied the mechanism of formation and the phase transition sequence occurring during the synthesis of bicontinuous cubic mesoporous phase. It was found that the changes in the surfactant packing parameter, dictated by the time-and temperature-dependent reaction parameters, result in a hexagonal ! lamellar ! hexagonal ! cubic phase transition sequence. In this article, we present a small angle X-ray scattering (SAXS) in situ study of a new preparation procedure of the bicontinuous cubic (Ia3d) phase in which an organic base is used as a reaction catalyst. The coexisting hexagonal and lamellar phases detected at an early reaction stage could indicate their importance in the formation of a cubic (Ia3d) mesophase. We found that the ®nal cubic phase is formed only when heat is applied. The cubic phase is formed by the collapse of a preceding hexagonal phase, where a given hexagonal plane (1 0 0) evolves to a cubic plane (2 1 1) having the same interplanar distance. Ó

Journal of the American Chemical Society, 2003

The unique properties of inorganic, mesoporous materials templated by supramolecular surfactant a... more The unique properties of inorganic, mesoporous materials templated by supramolecular surfactant aggregates include a narrow pore size distribution, high specific surface area, high specific pore volume, and a tunable pore diameter. The mechanism of formation of these materials is now quite well understood, due to careful in situ studies, as recently reviewed by Patarin et al. 1 There is now some agreement in that the early stages of formation involve (i) hydrolysis of the silicate precursor, (ii) condensation of silicate units leading to oligomeric/polymeric silica, (iii) the binding of surfactant to oligomeric/polymeric inorganic species paralleled by a cooperative self-assembly into a mesoscopically ordered inorganic-surfactant phase concentrated in surfactant and in silicate polyions. The phase-separation process increases the local concentration of inorganic species facilitating further condensation into a rigid framework. Much less work has been devoted to the use of surfactant mixtures as structure-directing agents, and only a few reports 2,3 concern the use of a mixture of anionic and cationic surfactants for this purpose. However, catanionic surfactant mixtures are known to form extended rodlike micelles already at low concentration and also to readily form lamellar phases in aqueous solution. Furthermore, the formation of vesicles is often observed in these systems as well. These effects are connected to the charge neutralization by ion-pairing coupled with the release of hydration water and screening, which leads to a pronounced increase in the surfactant packing parameter, to values higher than that of the individual surfactants. 10 Furthermore, nonideal mixing effects may also be involved in the stabilization of vesicular structures in these systems. Recently, we have used a mixture of oppositely charged surfactants, cetyltrimethylammonium bromide, CTAB, and 1-alkyl carboxylates, as structure-directing agents in the room-temperature synthesis of mesoscopically ordered silica under alkaline conditions. 3 A 2D hexagonal-to-lamellar phase transition was observed with increasing decanoate (DA)/CTAB molar ratio by X-ray diffraction (XRD), in agreement with the expected increase in the surfactant packing parameter. Furthermore, very extended thin silica sheets of uniform thickness were observed for calcined samples by transmission electron microscopy (TEM). 3b To study the possible formation of silicate-surfactant vesicles during the course of the reaction, an in situ cryogenic-TEM 4 (Cryo-TEM) study was performed on a selected aqueous system, where the lamellar phase dominates. In Cryo-TEM one studies the supramolecular structure in solution by vitrifying in liquid ethane a drop of solution on a TEM grid without staining or drying the sample. 5 The sample is further imaged under liquid nitrogen temperature in the TEM. Cryo-TEM has previously been shown to give very detailed information on the formation mechanism of cationic surfactant-templated mesoscopically ordered, MCM-41type silica. The synthesis has been described in detail in ref 3. The final molar composition was 157/3/0.15/1/0.062/1.48 H 2 O/NH 3 / CTAB/TEOS/DA/toluene. The reaction was quenched to prepare cryo-TEM samples by vitrification at different points in time after addition of the TEOS. A combination of two images recorded after a reaction time of 85 s of different parts of the sample is shown in . Very extended disordered rodlike micelles, with contour lengths exceeding 1 µm, are observed throughout the sample. The micelles are interconnected in junctions, 7 which are indicated by arrows in . Some other areas in the grid show a more developed network formation .

Characterization of microencapsulated liposome systems for the controlled delivery of liposome-associated macromolecules

Journal of Controlled Release, 1997

This paper describes the preparation and characterization of microencapsulated liposome systems (... more This paper describes the preparation and characterization of microencapsulated liposome systems (MELs) for the controlled delivery of liposome-associated macromolecules. Liposomes were encapsulated within microspheres of calcium-crosslinked alginate, with ...

Journal of Colloid and Interface Science, 2008

The dispersion of nanotubes by pH-responsive polymers (i.e., weak polyelectrolytes) enables the m... more The dispersion of nanotubes by pH-responsive polymers (i.e., weak polyelectrolytes) enables the macroscopic properties of aqueous suspensions to be tuned. Microstructural changes were achieved as a function of pH in aqueous suspensions containing single-walled carbon nanotubes and imaged by cryogenic-TEM. Clear evidence of pH-sensitive nanotube dispersion is shown. We expect that many useful properties of these nanotube-polymer systems could be sensitive to microstructure, making this technique important for aqueous processing of carbon nanotubes and macroscopic tailoring of solid polymer nanocomposite behavior.

Phase transitions in O/W lauryl acrylate emulsions during phase inversion, studied by light microscopy and cryo-TEM

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009

... b Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, I... more ... b Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel. c The Ilse Katz Center for Meso and Nanoscale Science and Technology,Ben-Gurion University of the Negev, Beer Sheva 84105, Israel. ...

Chemical Communications, 2008

Single-walled carbon nanotubes were found to induce elongation and alignment of surfactant micell... more Single-walled carbon nanotubes were found to induce elongation and alignment of surfactant micelles in thin films under the action of shear, leading to the formation of ordered arrays over micron lengths.

Worm-Like Soft Nanostructures in Nonionic Systems: Principles, Properties and Application as Templates

Journal of Nanoscience and Nanotechnology, 2013

The principles, occurrence, structure and properties of worm-like micellar solutions in nonionic ... more The principles, occurrence, structure and properties of worm-like micellar solutions in nonionic surfactant systems is reviewed, with focus in certain experimental methods used to characterize such soft nanostructured systems. Formulation plays a critical role in the design of worm-like micellar systems and derived viscoelastic networks. Micellar growth in one dimension, and hence formation of worm-like aggregates, is favoured by an increase in the average surfactant molecular packing parameter. Such an increase can be induced by addition of cosurfactant or amphiphilic oil that tends to penetrate in the surfactant palisade layer and reduce the specific surface area. On the other hand, long and bulky oils prone to be solubilized in the micellar core, cause a rod-sphere transition and therefore a decrease in viscosity. Salts have a small effect on the behaviour of nonionic worm-like micelles, contrary to what is found for ionic surfactant systems. The effect of raising temperature on worm-like micellar solutions is the result of a balance between the dehydration of the surfactant head groups, which favors elongation, the kinetics of micellar disruption and the formation of structures with nearly zero curvature. Therefore, a viscosity maximum as a function of temperature is found in many systems. Reverse worm-like micelles with a hydrophilic core can also be formed in organic solvents, even in the absence of ionic components or water. Worm-like micelles are useful as templates for the formation of ordered mesoporous oxides. The interaction of micelles with silica species results in the formation of silica-surfactant complexes that later precipitate as hexagonal phase via a cooperative mechanism.