Confined straight and branched CdSe nanowires (NWs) are synthesized using a solutionbased approach which leverages advances in the synthesis of colloidal CdSe quantum dots (QDs) with incipient approaches for the seeded (solution) synthesis of semiconductor NWs. The resulting straight and branched NWs have typical diameters below 10 nm with accompanying lengths between 1 and 10 µm. In the case of branched NWs, tripod, v-shaped, and y-shaped morphologies are observed. Variations in this preparation lead to higher order structures with multiple arms. The branching transition is discussed, and a possible mechanism based upon geminate NW nucleation is proposed. Such solution-grown straight, branched, and higher-order NWs exhibit potentially interesting optical, electrical, and transport properties due to their narrow radii below the corresponding bulk exciton Bohr radius of CdSe. Furthermore, this transition from straight to branched morphologies opens up avenues for investigating not only size-but also shape-dependent optical/electrical properties of one-dimensional (1D) and quasi-1D materials.

Fluorescently Labeled PEG-Peptide Synthesis: Peptides RGDS (American Peptide) and REDV (American Peptide) were conjugated to PEG ) by reaction with ACRL-PEG-NHS (Nektar, NHS: N-hydroxysuccinimide) in a 1:1 molar ratio for 2 h in 50 mM sodium bicarbonate buffer, pH 8.5. Alexa Fluor 488 carboxylic acid, tetrafluorophenyl (TFP) ester (Molecular Probes) was then added to the ACRL-PEG-RGDS reaction mixture at approximately 10 moles dye per mole PEG-peptide and allowed to react for 1 h at room temperature. Alexa Fluor 594 carboxylic acid, TFP ester (Molecular Probes) was similarly added to the ACRL-PEG-REDV and allowed to react for 1 h at room temperature. The desired products were purified by dialysis and then lyophilized.Photopolymerization of PEGDA Hydrogels: A solution was prepared containing 10 % (w/v) PEGDA and 1.5 % (v/v) triethanolamine (TEOA) in N-(2-hydroxylethyl)piperazine-N′-(2-ethanesulfonic acid) (HEPES)-buffered saline (pH 7.4, HBS), 0.4 % (v/v) N-vinylpyrrolidone (NVP), and 100 lM eosin Y (a biocompatible, visible-light photoinitiator). This solution was polymerized between two glass plates separated by 0.5 mm spacers by exposure to white light.Laser Scanning Lithography: The surface of a pre-swelled PEGDA hydrogel was positioned at the focal plane of a 10× Plan-Apochromat objective (numerical aperture (NA) 0.45) attached to a LSM 510 META confocal microscope (Zeiss). Virtual masks were drawn using the ROI function of the LSM software.Two-Dimensional Surface Patterns: A thin layer of fluorescently labeled ACRL-PEG-peptide (30 lmol mL -1 ) dissolved in HBS/TEOA containing 0.4 % NVP and 100 lM eosin Y was spread onto the surface of the PEGDA gel. For the fluorescence pattern images in Figures 1,2a,3, patterning was carried out using an irradiation cycle in which a 514 nm argon ion laser line was unidirectionally scanned across the specified ROIs at 0.30 mW lm -2 and 60 ls lm. Unbound ACRL-PEG-peptide was rinsed away with sterile PBS. For the gradient patterns in Figures 2b-d, 514 nm argon ion laser power was maintained at 0.30 mW lm -2 ; however, a range of irradiation times were used across ROIs, with a minimum exposure time of 0.5 ls lm -2 . Successful patterning of the fluorescently labeled peptides was confirmed by visualization under fluorescence (Zeiss LSM 510 META). The bioactivity of patterned cell adhesion peptide RGDS was evaluated by seeding HDFs onto patterned hydrogel surfaces and examining cell adhesion via DIC imaging (Zeiss LSM 510 META) at days 1 and 4.Three-Dimensional Surface Patterns: A thin layer of 0.2 g mL -1 MW 600 g mol -1 PEGDA (Sarcomer) dissolved in HBS/TEOA containing 0.4 % NVP and 100 lM eosin Y was spread onto the surface of the PEGDA gel. Patterning was carried out using an irradiation cycle in which a 514 nm argon ion laser line was unidirectionally scanned across the specified ROIs at 0.30 mW lm -2 and 60 ls lm -2. Unbound ACRL-PEG-peptide was rinsed away with sterile PBS, and patterning was confirmed through DIC imaging (Zeiss LSM 510 META). The optical, electrical, an...

The synthesis of narrow diameter (<10 nm) straight and branched PbSe nanowires (NWs) using a seeded solution approach is described. Solution-based PbSe NWs are obtained by injecting a solution consisting of trioctylphosphine selenide (TOPSe) and Au/Bi core/shell nanoparticles (NPs) into a mixture composed primarily of a mild coordinating solvent, a fatty acid, and a Pb precursor at moderate temperatures. The resulting NWs have diameters between 5 and 10 nm and lengths ranging from 1 to 5 µm. High-resolution transmission electron microscopy (TEM) reveals that the NWs exhibit a high degree of crystallinity and grow along the 〈100〉 directions of the lattice. By varying the initial reaction conditions, in particular the Pb to Se precursor ratio, branched NWs can be obtained. The growth mechanism appears similar to the case of analogous (branched) CdSe NWs, although the underlying rock salt structure of PbSe leads to right angles and t-shapes as opposed to CdSe, where v-shape, y-shape, and tripod morphologies are observed due to its underlying zinc blende and wurtzite lattices. In addition, "mergedy" NWs and higher order structures exhibiting multiple branching points are observed. Both straight and branched NWs have radii well below the bulk exciton Bohr radius of PbSe (46 nm), opening up opportunities for interesting optical and electrical studies of strong confinement in this system. The current investigation also sheds additional light on the mechanism behind self-induced branching in onedimensional (1D) nanowires.

Summary Hydraulic-fracturing fluids are used to break down subterranean formations where oil and gas are trapped. Pad or prepad fluids are first pumped into the formation to generate the fracture geometry. Once the fracture geometry is created, additional fluid containing proppant is used to transport these solid particles into the fractures. Then, the hydraulic pressure is released and the fracture will tend to close. At that stage, the proppant prevents fracture closure and provides a conductive channel for hydrocarbons to flow into the wellbore. Biopolymers, synthetic polymers, foams, viscoelastic surfactant (VES) fluids, and slickwater are all used as fracturing fluids, each with properties that are beneficial under certain conditions. Today, their formulations are well-developed, and more recently, may incorporate small-sized particles in the nanometer size range. Such nanoparticles have addressed certain technological limitations of fracturing fluids. For example, VES fluids were reported to suffer high leakoff rates in moderate permeability reservoirs (200 md) and were limited in temperature (beyond approximately 220°F, viscosity was diminished significantly). Another challenge is the pressure-dependent behavior of borate-crosslinked gels, where the viscosity was found to drop significantly under high pressures. Also, in high-temperature reservoirs (&gt;350°F), it is very challenging to design a fluid that can sustain enough viscosity for a required period of time. Synthetic polymers (mainly acrylamide-based polymers) are commonly used and have been reported to be used at high concentrations. These high-concentration requirements are imposed by the need for a stable viscosity under high-temperature conditions. High polymer loading increases the potential of formation damage caused by the fluid residue. These challenges, which can be addressed by nanotechnology, could have a major impact on hydraulic-fracturing applications. For instance, the working temperature limit of VES-based fluids was improved from 200 to 250°F (93 to 121°C) by adding zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles. The borate-crosslinked gels were found to maintain their viscosity at pressures up to 20,000 psi when using boronic acid-functionalized nanolatex silica particles as crosslinkers, while under such high pressures, conventional borate crosslinkers showed more than 80% reduction in viscosity. Moreover, the rheological properties of mixed VES/polymer fluids were enhanced when using nanoparticles. Use of foams can reduce the amount of water consumed in hydraulic fracturing. Alfa olefin sulfonate (AOS) surfactant can be foamed by use of carbon dioxide (CO2). Aluminum oxide nanoparticles were found to stabilize the foams created by AOS, VES, and CO2. This has a potential application in waterless fracturing. This review paper will capture all of these aspects and summarize the most recent experience of nanoparticle usage in hydraulic-fracturing fluids design.

Oil and gas production from shale formations has proven to be economical because of advances in hydraulic fracturing but remains very challenging in part because of the presence of the ductile, polymer nature of the hydrocarbon source material, kerogen. This organic matter is intertwined among silicates, aluminosilicates, and other minerals as fine laminae that weave among the shale rock fabric, adding soft mechanical cohesion to the material. A potential solution has been developed, a new type of reactive fracturing fluid composed of strong oxidizers such as bromate (BrO3 –), which could mitigate the adverse effects of the polymeric nature of kerogen on the hydraulic conductivity of the fractured shale formation. High-resolution scanning electron microscopy of kerogen-rich shale samples before and after fluid treatment demonstrates notable porosity enhancement evident by cracks forming in the macerals and augmenting the volumetric porosity. The stability of the reactive components at elevated reservoir temperatures in addition to the demonstrated results suggest the potential for measureable improvements in hydraulic conductivity and hence in the ultimate recovery of oil and gas from future hydraulic fracturing operations.

The geminal organodimetallic complexes [({Ph2P(NSiMe3)}2C)2M4], where M4=Na4, 3; Li2Na2, 4; LiNa3, 5; Li2K2, 6; Na2K2, 7, and Na3K, 8, have been prepared through a variety of methods including direct or sequential deprotonation of the neutral ligand with strong bases (tBuLi, nBuNa, (Me3Si)2NNa, PhCH2K or (Me3Si)2NK), transmetalation of the homometallic derivatives (M4=Li4, 2 or Na4, 3) with tBuONa or tBuOK, and by cation exchange upon mixing the homometallic complexes in an arene solution. Complexes 3-8 have been characterized by single-crystal X-ray diffraction and are found to form a homologous series of dimeric structures in the solid-state, in accord with the previously reported structure of 2. Each complex is composed of a plane of four metals, M4, in which the ligands adopt capping positions to form distorted M4C2 octahedral cores. The metals in homometallic complexes 2 and 3 define an approximate square, whereas the heterometallic derivatives 4-8 have distinctly rhombic arrangements. The lighter metals in 4-8 interact strongly with the carbanions and the heavier metals are pushed towards the periphery of the structures. 1H, 13C, 7Li, 31P, and 29Si multinuclear NMR spectroscopic studies, cryoscopic measurements, and electrospray ionization-mass spectroscopic studies are consistent with the dimers being retained in solution. Dynamic solution behavior was discovered for Li2Na2 complex 4, in which all five possible tetrametallic derivatives Li4, Li3Na, Li2Na2, LiNa3 and Na4 coexist. Density functional theory (DFT) and natural bond order (NBO) calculations in association with natural population analyses (NPA) reveal significant differences in the electronic structures of the variously metalated dianions. The smaller cations are more effective in localizing the double negative charge on the carbanion (in the form of two lone pairs), leading to differences in the distribution of the electron density within the ligand backbones. In turn, a complex interplay of hyperconjugation, electrostatics and metal-ligand interactions is found to control the resulting electronic structures of the geminal organodimetallic complexes.

Viscoelastic surfactants (VES) are used in upstream oil and gas applications, particularly hydraulic fracturing and matrix acidizing. A description of surfactant types is introduced along with a description of how they assemble into micelles, what sizes and shapes of micelles can be formed under different conditions, and finally how specific structures can lead to bulk viscoelastic-solution properties. This theoretical discussion leads into a description of the specific VES systems that have been used over the last 20 years in improved oil recovery for upstream applications.VES-based fluids have been used most extensively for hydraulic fracturing. They are preferred over conventional polymer-based fracturing-fluid systems because they are essentially solids-free systems that have demonstrated less damage to the reservoir-rock formation. In fact, approximately 10% of the fracturing treatments use VES-based fluids. Important advancements in VESs have been made by introducing "pseudocrosslinking agents," such as nanoparticles, to enhance the viscosity. Fracturing-fluid systems modeled after VES have also been improved recently by developing internal breakers to lower their viscosity to flow back the well. The flexibility of VES-based fluids has been demonstrated by their application as foamed fluids, as well as their incorporation with brine systems such as produced water.A second key area that has benefited from VES-based systems is matrix acidizing of carbonate-based reservoirs. The viscosity of these VES-based fluids is mostly controlled by pH; at low pH (low viscosity), the acid system flows easily and invades pore spaces in the formation. During acidizing, the acid is spent, and the pH and viscosity increase. Because the spent acid has higher viscosity, fresh acid is diverted to low-permeability, uncontacted zones and penetrates the rocks to form wormholes. A number of experimental studies and field applications to these effects have been performed and will be described in this study.In order for VES-based fluids to play a more-prominent role in the field, inherent limitations such as cost, applicable temperature range, and leakoff characteristics will need to continue to be addressed. If we can efficiently and economically overcome these issues, VES-based fluids offer the industry an excellent clean and nondamaging alternative to conventional polymer-based fluids.

The title disodio complex may be prepared by the double deprotonation of a neutral bis(phosphinimine) ligand using 2 equiv of the strong base n-BuNa, whereas the mixed Li/Na derivative can be prepared by controlled sequential deprotonation, by transmetalation, or by mixing the homometallic analogues. The compounds form dimers with the ligands capping an Na4 square or a Li2Na2 rhomboid, and these are the first examples of R2C2- dianions containing a heavy alkali metal to be structurally characterized.