Newtonian fluid mechanics, in which the shear stress is proportional to the strain rate, is synonymous with the flow of simple liquids such as water. We report the measurement and theoretical verification of non-Newtonian, viscoelastic flow phenomena produced by the high-frequency (20 GHz) vibration of gold nanoparticles immersed in water-glycerol mixtures. The observed viscoelasticity is not due to molecular confinement, but is a bulk continuum effect arising from the short time scale of vibration. This represents the first direct mechanical measurement of the intrinsic viscoelastic properties of simple bulk liquids, and opens a new paradigm for understanding extremely high frequency fluid mechanics, nanoscale sensing technologies, and biophysical processes. DOI: 10.1103/PhysRevLett.111.244502 PACS numbers: 47.50.Àd, 47.61.Àk, 62.25.Fg, 87.15.ht A fluid is said to be Newtonian if it exhibits a simple linear relationship between shear stress and strain rate. This description, which underlies conventional fluid dynamics, provides an excellent approximation to the behavior of real fluids, provided the time scale for measurement is long compared to the time required for stresses to propagate in the fluid. In simple liquids, including water and glycerol, these ''relaxation times'' are on the order of 1 ps-1 ns [1][2][3]. These time scales are short compared to the time scales associated with the motion of macroscopic objects in the fluids, which allows interactions between solid structures and simple fluids to be described by classical Navier-Stokes treatments [4,5]. These treatments hold even for micrometer-scale objects, such as the cantilevers found in atomic force microscopes and microelectromechanical devices, because they have characteristic vibrational frequencies in the kHz to MHz range [6,7]. Non-Newtonian fluid mechanics is therefore conventionally associated only with complex fluids that have long relaxation times, such as polymer solutions and melts, dense colloidal suspensions such as corn starch in water, and fluids near their phase transitions [8,9]. Scaling objects down to nanometer size scales increases their characteristic vibrational frequencies up to the GHz or THz range [10]. Fluid-structure interactions on these length scales thus have the potential to show significant deviations from Newtonian behavior, even for simple liquids.Departures from Newtonian behavior have been reported for simple liquids under extreme confinement, due to structural reorganization and surface effects on the molecular scale [11][12][13]. For bulk fluids, by contrast, direct mechanical observation of non-Newtonian behavior has been limited to solid structures interacting with dilute gases [14]. In this case, the effects can be predicted rigorously by the Boltzmann equation [15]. For simple bulk liquids, however, rigorous theoretical description of, and experimental access to, the non-Newtonian regime remain outstanding problems in the physical sciences.We access this regime directly for the first time by exciting a...

Colloidal perovskite nanocrystals support bright, narrow PL tunable over the visible spectrum. However, bandgap tuning of these materials remains limited to laboratory-scale syntheses. In this work, we present a polar-solvent-free ligand-mediated transport synthesis of high-quality organic-inorganic perovskite nanocrystals under ambient conditions with photoluminescence quantum yields up to 97%. Our synthesis employs a ligand-mediated transport mechanism that circumvents the need for exquisite external control (e.g., temperature control, inert-gas protection, dropwise addition of reagents) required by other methods due to extremely fast reaction kinetics. In the ligand-mediated transport mechanism, multiple equilibria cooperatively dictate reaction rates and enable precise control over NC size. These small nanocrystals exhibit high photoluminescence quantum yields due to quantum confinement. Nanosecond transient absorption spectroscopy experiments reveal a fluence-independent PL decay originating from exciton recombination. Two-dimensional electronic spectroscopy resolves multiple spectral features reflecting the electronic structure of the nanocrystals. The resolved features exhibit size-dependent spectral positions, further indicating the synthesized nanocrystals are quantum-confined.

We present a facile methodology for the end-to-end assembly of gold nanorods of various aspect ratios on corrugated, horizontal, cylinder-forming diblock copolymer templates. Although the depth of corrugation is significantly smaller than the diameter of the nanorods, they exhibit excellent selectivity (>98%) and alignment for placement in the polymer grooves due to capillary forces and the substrate's topography. Enhanced corrugation of the diblock template is achieved by chemical swelling prior to deposition of the metallic nanorods. Graphoepitaxy of the diblock copolymer in nanoconfining channels is employed to achieve essentially perfect long-range orientation of the substrate, while subsequent deposition of nanorod arrays whose alignment maps onto that of the diblock template with high fidelity provides novel organic−inorganic hybrid surfaces whose surface enhanced Raman spectroscopy (SERS) properties are characterized. These arrays of aligned gold nanorods exhibit polarization-dependent spectra for adsorbed molecular species with a 24-fold enhancement in signal intensity when the trenches are aligned with parallel versus perpendicular orientation with respect to the incident polarization of the excitation laser. The simple construction of these systems and their unique SERS properties provide a new and efficacious platform for the construction of functional nanodevices. ■ INTRODUCTIONThin films of nanoparticles (NPs) have attracted considerable attention due to their potential applications related to electronic devices, 1,2 magnetic storage, 3 and sensors. 4,5 Investigations into the last category have focused on noble metal NPs due to their well-documented surface enhanced Raman spectroscopic (SERS) properties. 5−7 Gold NP (AuNP) SERS systems are typically fabricated using either top-down or bottom-up techniques, where the regions of electric field enhancement, called hot spots, are made by electron beam lithography (EBL) 8,9 or ion-beam sputtering 10 or through the deposition of colloidally synthesized AuNPs. Controlling the deposition of colloidal AuNPs is attractive because the locations of the hot spots are determined by the order and alignment of the AuNPs on the substrate. This has been done by chemically functionalizing 11−14 or patterning 12,15−20 the substrates or by modifying the AuNP colloid. 21−23 This paper presents a facile, bottom-up technique that produces highly ordered arrays of colloidal gold nanorods (AuNRs) aligned end-to-end with favorable and polarizationdependent SERS properties. AuNRs have received particular attention due to their controllable syntheses, 24−28 tunable plasmon resonances, 29 and electromagnetic field enhancements, 30 making these NPs 6 and their assemblies 7 of interest for SERS. 7,20,23 Coupling between plasmonic NPs makes AuNR assemblies exhibit stronger hot spots than individual structures and increases the SERS response, 7 as documented for AuNR chains 21,31,32 and for various large-scale 2D and 3D AuNR aggregates. 20,23,33 The AuNR arrays presented in this p...

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An aqueous synthesis of gold bipyramid dimers is presented. The methodology, its selectivity, and the characterization of the resulting structures with optical dark-field and scanning electron microscopy are presented and discussed. In the bowtie orientation, the dimers exhibit a 20% red shift in their plasmon resonance as compared to the individual particles, with a weak dependence on the interparticle separation. From the analysis, it was found that the in situ absorption peaks that develop during the assembly can be assigned to specific dimer structures, which has not been shown previously. Last, the kinetics of the assembly are analyzed.

A new technical standard has been developed for assessing the performance and physical characteristics of heavy brines used in completion, packer, and drill-in operations. This technical standard includes procedures for evaluating the density, specific gravity, clarity, amount of suspended particulate matter, crystallization point, pH, and iron contamination. It also contains a discussion of gas hydrate formation and mitigation, brine viscosity, brine crystallization at high pressures, corrosion testing, buffering capacity, and a standardized reporting form. Introduction The American Petroleum Institute (API) has developed recommended practices (RP) for testing heavy brines. These recommended practices have been generated and documented by brine experts from industry under the auspices of API Committee 3, Subcommittee 13, Task Group 6. The first recommended practice for clear completion brines was published June 1, 1986 as "API Recommended Practice 13J Recommended Practice for Testing Heavy Brines" (RP-13J) [1]. This document contained three sections: Brine Density, Brine Crystallization Temperature, and Brine Clarity. Each section of the document was enhanced in the Second Edition[2] published March 1996. The Third Edition[3] was published December 2003 and greatly expanded the scope of RP-13J. In addition to substantially upgrading the existing sections of the document, the Third Edition added four new sections and six annex sections. The new additions to RP-13J are titled:Section 9Solids evaluation by gravimetric procedures,Section 10pH,Section 11Iron contamination,Section 12Daily completion fluid report,Annex ACompletions Fluid Report Form,Annex BGas Hydrates,Annex CBuffering capacity of brines,Annex DPressure crystallization of brines,Annex EBrine viscosity, andAnnex FPrinciple of corrosion testing. As we entered into the 21st Century, it became abundantly clear that recommended practices and standards needed to be globalized. Consequently, the API and authors of the Third Edition of RP-13J transformed that edition into the format required by the International Organization for Standardization (ISO). The resulting document, " Petroleum and natural gas industries- Completion fluids and materials- Part 3: Testing of heavy brines" [4] was generated and given the designation "ISO 13503–3: Testing of heavy brines" or more commonly ISO 13503–3. As of this writing, the document was being circulated in Final Draft for vote that will conclude in November 2005. This document and its counterpart API RP-13J (3rd Edition) are "living documents" that undergo continual enhancement. By convening appropriate work groups, Task Group 6 will continue to expand and update the documents, and provide procedures and standards for new sections such as buffering capacity and pressure crystallization. The purpose of this paper is to communicate information about the document "ISO 13503–3: Testing of heavy brines" to the oilfield industry, particularly to those engineers involved with the use and maintenance of clear completion brines.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA new technical standard has been developed for assessing the performance and physical characteristics of heavy brines used in completion, packer, and drill-in operations. This technical standard includes procedures for evaluating the density, specific gravity, clarity, amount of suspended particulate matter, crystallization point, pH, and iron contamination. It also contains a discussion of gas hydrate formation and mitigation, brine viscosity, brine crystallization at high pressures, corrosion testing, buffering capacity, and a standardized reporting form.

Use of a Non-Aqueous Drilling Fluid (NADF) on the Chuandongbei (CDB) gas project wells will increase the rate of penetration (ROP) and decrease non productive time (NPT) and thus the overall development costs. The use of non aqueous fluids instead of water based drilling fluids (WBM) will however, require significant changes and improvements to the waste management practices previously used in the region which are not suitable for use with non aqueous drilling fluids. A non-aqueous drilling fluid based on a proprietary synthetic paraffin base fluid and a potassium acetate internal phase will be used to maximize the bioremediation potential of the drilling fluid and allow the use of an enhanced bioremediation process that combines the use of fertilizer, top soil and organic amendments to speed up the rate of degradation to produce a useful soil that is able to support plant growth that can be used for reclamation and landscaping of the drill site. This paper provides a concise overview of the proof of concept studies that were carried out at the University of Tulsa (Phase I and II) and the subsequent refinements using locally sourced soils and organic amendments at the South Western Petroleum University in China (Phase III). The data show that the synthetic based drilling fluid can be successfully biodegraded in soil bio-piles composed of soil and organic amendments from the CDB operating area. The resultant product was successfully used as a plant growth medium.