Monitoring oil displacement processes with k‐t accelerated spin echo SPI

Magnetic resonance imaging (MRI) is a robust tool to monitor oil displacement processes in porous media. Conventional MRI measurement times can be lengthy, which hinders monitoring time‐dependent displacements. Knowledge of the oil and water microscopic distribution is important because their pore scale behavior reflects the oil trapping mechanisms. The oil and water pore scale distribution is reflected in the magnetic resonance T₂ signal lifetime distribution. In this work, a pure phase‐encoding MRI technique, spin echo SPI (SE‐SPI), was employed to monitor oil displacement during water flooding and polymer flooding. A k‐t acceleration method, with low‐rank matrix completion, was employed to improve the temporal resolution of the SE‐SPI MRI measurements. Comparison to conventional SE‐SPI T₂ mapping measurements revealed that the k‐t accelerated measurement was more sensitive and provided higher‐quality results. It was demonstrated that the k‐t acceleration decreased the average measurement time from 66.7 to 20.3 min in this work. A perfluorinated oil, containing no ¹H, and H₂O brine were employed to distinguish oil and water phases in model flooding experiments. High‐quality 1D water saturation profiles were acquired from the k‐t accelerated SE‐SPI measurements. Spatially and temporally resolved T₂ distributions were extracted from the profile data. The shift in the ¹H T₂ distribution of water in the pore space to longer lifetimes during water flooding and polymer flooding is consistent with increased water content in the pore space. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental investigation on spontaneous counter‐current imbibition in water‐wet natural reservoir sandstone core using MRI

Counter‐current imbibition is a process whereby a wetting phase spontaneously imbibes into a porous media, displacing the non‐wetting phase. This process is considered an important oil recovery mechanism during water flooding in fractured oil reservoirs. In this study, the dynamic process of counter‐current imbibition for a natural reservoir sandstone core with an all‐face‐open boundary condition was monitored using magnetic resonance imaging (MRI). A series of images and relaxation time T₁ spectra were acquired. The movement of water spontaneously entering the core sample while oil escapes, the spatial distribution of oil and water, and the in situ saturation change of oil and water in porous media can be accurately detected using MRI. MRI assists the direct evaluation of the basic mechanisms of imbibitions. Experimental results suggest the remaining oil was trapped in some large pores because of the capillary pressure, and the oil recovery in some large‐pore regions is lower than that in some small‐pore regions at the end of imbibition. Experimental findings show a close agreement between conventional material balance and oil recovery determined from MRI. The in situ oil recovery data agree well with the empirical models. The observations from MRI images could provide test cases to enable the development of mathematical models and to facilitate the evaluation of the proposed imbibition mechanisms. Copyright © 2016 John Wiley & Sons, Ltd.     

Dispersion‐solidification liquid–liquid microextraction for volatile aromatic hydrocarbons determination: Comparison with liquid phase microextraction based on the solidification of a floating drop

Two microextraction techniques – liquid phase microextraction based on solidification of a floating organic drop (LPME‐SFO) and dispersive liquid–liquid microextraction combined with a solidification of a floating organic drop (DLLME‐SFO) – are explored for benzene, toluene, ethylbenzene and o‐xylene sampling and preconcentration. The investigation covers the effects of extraction solvent type, extraction and disperser solvents' volume, and the extraction time. For both techniques 1‐undecanol containing n‐heptane as internal standard was used as an extracting solvent. For DLLME‐SFO acetone was used as a disperser solvent. The calibration curves for both techniques and for all the analytes were linear up to 10 μg/mL, correlation coefficients were in the range 0.997–0.998, enrichment factors were from 87 for benzene to 290 for o‐xylene, detection limits were from 0.31 and 0.35 μg/L for benzene to 0.15 and 0.10 μg/L for o‐xylene for LPME‐SFO and DLLME‐SFO, respectively. Repeatabilities of the results were acceptable with RSDs up to 12%. Being comparable with LPME‐SFO in the analytical characteristics, DLLME‐SFO is superior to LPME‐SFO in the extraction time. A possibility to apply the proposed techniques for volatile aromatic hydrocarbons determination in tap water and snow was demonstrated.     

DTPA-BpABA与锰配合物的结构表征和弛豫研究

X-ray single crystal analysis of a new paramagnetic manganese（Ⅱ） complex with DTPA-BpABA （a DTPAbisamide derivative）, Mn（DTPA-BpABA）·4H2O, shows that four oxygen atoms and three nitrogen atoms from the ligand coordinate to Mn（Ⅱ） cation, forming a seven-coordinate distorted pentagonal bipyramid polyhedron. In the crystal, the carboxyl groups and the nitrogen atoms extensively form hydrogen bonds with the lattice water molecules, building a 3D-network. The relaxometric study indicates that the R1 value of the paramagnetic manganese（Ⅱ）complex is 5.12 mmol·L·s^-1. The higher R1 value means that this complex may find an application in magnetic resonance imaging （MRI） technique.     

A comparison of magnetic resonance imaging methods for fluid content imaging in porous media

Quantitative measurements are important for imaging fluid content in porous media. Conventional MRI methods suffer from contrast because of relaxation times in porous media, resulting in measurements of apparent fluid content, not the true fluid content. We compare four magnetic resonance imaging methods for fluid content imaging in several water‐saturated reservoir core plugs: frequency‐encoded spin echo, single point ramped imaging with T₁ enhancement, hybrid spin echo single point imaging (SE‐SPI), and T₂ mapping SE‐SPI. 1‐D profiles obtained with each method were compared in terms of image quality, image sensitivity, and quantification of water content. The image quality of short T₂ lifetime samples suffered from blurring in hybrid SE‐SPI images. Image sensitivity was the highest in the profiles obtained with frequency‐encoded spin echo. The quantification of frequency‐encoded spin echo, T₂ mapping SE‐SPI, and hybrid SE‐SPI suffered in core plugs with a significant population of short T₂ components because of T₂ attenuation. Overall, single point ramped imaging with T₁ enhancement was found to be the most general method for fluid content imaging. Copyright © 2013 John Wiley & Sons, Ltd.     

Roaming dynamics in acetone dissociation

DC slice imaging has been employed to study the photodissociation dynamics of acetone at 230 nm, with detection of the CO photoproduct via the B (v' = 0) (1)Sigma(+) <-- X (v' = 0) (1)Sigma(+) transition. A bimodal translational energy distribution observed in the CO fragments points to two distinct dissociation pathways in the 230 nm photolysis of acetone. One pathway results in substantial translational energy release (E(ave) approximately 0.3 eV) along with rather high rotational excitation (up to J' = 50) of CO, and is attributed to the thoroughly investigated stepwise mechanism of bond cleavage in acetone. The other dissociation pathway leads to rotationally cold CO (J' = 0-20) with very little energy partitioned into translation (E(ave) approximately 0.04 eV) and in this way it is dynamically similar to the recently reported roaming mechanism found in formaldehyde and acetaldehyde dissociation. We ascribe the second dissociation pathway to an analogous roaming dissociation mechanism taking place on the ground electronic state following internal conversion. For acetone, this would imply highly vibrationally excited ethane as a coproduct of rotationally cold CO, with the ethane formed above the threshold for secondary decomposition. We estimate that about 15% of the total CO fragments are produced through the roaming pathway. Rotational populations were obtained using a new Doppler-free method that simply relies on externally masking the phosphor screen under velocity map conditions in such a way that only the products with no velocity component along the laser propagation direction are detected.     

Velocity of a Molecule Evaporated from a Water Nanodroplet: Maxwell–Boltzmann Statistics versus Non‐Ergodic Events

The velocity of a molecule evaporated from a mass‐selected protonated water nanodroplet is measured by velocity map imaging in combination with a recently developed mass spectrometry technique. The measured velocity distributions allow probing statistical energy redistribution in ultimately small water nanodroplets after ultrafast electronic excitation. As the droplet size increases, the velocity distribution rapidly approaches the behavior expected for macroscopic droplets. However, a distinct high‐velocity contribution provides evidence of molecular evaporation before complete energy redistribution, corresponding to non‐ergodic events.     

Poly(bis‐2,2,2‐trifluoroethoxymethyl oxetane): Multiple crystal phases,crystallization‐induced surface topological complexity and enhanced hydrophobicity

Semicrystalline poly(bis‐trifluoroethoxymethyl)oxetane, P(B‐3FOx), was prepared by cationic ring‐opening polymerization at ?5 °C with M_n up to 21 kDa. Differences in cooling rates from the melt have substantial effects on crystal phase, percent crystallinity, surface topography, and wetting behavior. DSC and WAXD show that cooling from the melt at slow rates (<5 °C/min) gives α‐P(B‐3FOx) with ΔH_f = 22–27 J/g. Quenching from the melt results in β‐P(B‐3FOx) for which a mesophase structure is suggested. β‐P(B‐3FOx) melts at 53 °C followed by recrystallization to α‐P(B‐3FOx). Solution casting from THF results in third phase, γ‐P(B‐3FOx). TM‐AFM and SEM imaging for α‐P(B‐3FOx) showed that cold crystallization at 25 °C brought about increased crystallinity and surface topologies characterized by sharp asperities and lath‐shaped crystals. Spontaneous surface roughening of α‐P(B‐3FOx) results in a discontinuous three‐phase contact line with water and an increase in water sessile drop contact angle from 106° to 136°. The ～30° increase in water contact angle was attributed primarily to a topological change from a relatively smooth surface (Wenzel state) to an asperity‐rich surface yielding a discontinuous three‐phase contact line (composite of Wenzel and Cassie‐Baxter state). The oleophobicity for this polymer, which contains only a single ? CF₃ end group on each side chain, compares favorably with more highly fluorinated acrylates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1022–1034, 2010     

Comparative Adsorption of Acetone on Water and Ice Surfaces

Small organic molecules on ice and water surfaces are ubiquitous in nature and play a crucial role in many environmentally relevant processes. Herein, we combine surface‐specific vibrational spectroscopy and a controllable flow cell apparatus to investigate the molecular adsorption of acetone onto the basal plane of single‐crystalline hexagonal ice with a large surface area. By comparing the adsorption of acetone on the ice/air and the water/air interface, we observed two different types of acetone adsorption, as apparent from the different responses of both the free O?H and the hydrogen‐bonded network vibrations for ice and liquid water. Adsorption on ice occurs preferentially through interactions with the free OH group, while the interaction of acetone with the surface of liquid water appears less specific.     

Organic Nanoprobes for Fluorescence and 19F Magnetic Resonance Dual‐Modality Imaging

Multimodal imaging techniques have been demonstrated to be greatly advantageous in achieving accurate diagnosis and gained increasing attention in recent decades. Herein, we present a new strategy to integrate the complementary modalities of ¹⁹F magnetic resonance imaging (¹⁹F MRI) and fluorescence imaging (FI) into a polymer nanoprobe composed of hydrophobic fluorescent organic core and hydrophilic fluorinated polymer shell. The alkyne‐terminated fluorinated copolymer (Pn) of 2,2,2‐trifluoroethyl acrylate (TFEA) and poly(ethylene glycol) methyl ether acrylate (PEGA) was first prepared via atom transfer radical polymerization (ATRP). The PEGA plays an important role in both improving ¹⁹F signal and modulating the hydrophilicity of Pn. The alkynyl tail in Pn is readily conjugated with azide modified tetra‐phenylethylene (TPE) through click chemistry to form azo polymer (TPE‐azo‐Pn). The core‐shell nanoprobes (TPE‐P3N) with an average particle size of 57.2 ± 8.8 nm are obtained via self‐assembly with ultrasonication in aqueous solution. These nanoprobes demonstrate high water stability, good biocompatibility, strong fluorescence and good ¹⁹F MRI performance, which present great potentials for simultaneous fluorescence imaging and ¹⁹F–MR imaging.     

Design of a Gd‐DOTA‐Phthalocyanine Conjugate Combining MRI Contrast Imaging and Photosensitization Properties as a Potential Molecular Theranostic

The design and synthesis of a phthalocyanine – Gd‐DOTA conjugate is presented to open the way to novel molecular theranostics, combining the properties of MRI contrast imaging with photodynamic therapy. The rational design of the conjugate integrates isomeric purity of the phthalocyanine core substitution, suitable biocompatibility with the use of polyoxo water‐solubilizing substituents, and a convergent synthetic strategy ended by the use of click chemistry to graft the Gd‐DOTA moiety to the phthalocyanine. Photophysical and photochemical properties, contrast imaging experiments and preliminary in vitro investigations proved that such a combination is relevant and lead to a new type of potential theranostic agent.     

Flash nanoprecipitation with Gd(III)‐based metallosurfactants to fabricate polylactic acid nanoparticles as highly efficient contrast agents for magnetic resonance imaging

Polylactic acid (PLA) nanoparticles coated with Gd(III)‐based metallosurfactants (MS) are prepared using a simple and rapid one‐step method, flash nanoprecipitation (FNP), for magnetic resonance imaging (MRI) applications. By co‐assembling the Gd(III)‐based MS and an amphiphilic polymer, methoxy poly(ethylene glycol)‐b‐poly(?‐caprolactone) (mPEG‐b‐PCL), PLA cores were rapidly encapsulated to form biocompatible T₁ contrast agents with tunable particle size and narrow size distribution. The hydrophobic property of Gd(III)‐based MS were finely tuned to achieve their high loading efficiency. The size of the nanoparticles was easily controlled by tuning the stream velocity, Reynolds number and the amount of the amphiphilic block copolymer during the FNP process. Under the optimized condition, the relaxivity of the nanoparticles was achieved up to 35.39 mM^?1 s^?1 (at 1.5 T), which is over 8 times of clinically used MRI contrast agents, demonstrating the potential application for MR imaging.     

Subdiffraction‐Resolution Fluorescence Microscopy of Myosin–Actin Motility

Subdiffraction‐resolution imaging by subsequent localization of single photoswitchable molecules can achieve a spatial resolution in the range of ～20 nm with moderate excitation intensities, but have so far been too slow for imaging faster dynamics in biology. Herein, we introduce a novel approach for video‐like subdiffraction microscopy based on rapid and reversible photoswitching of commercially available organic carbocyanine fluorophores. With the present concept, we demonstrate in vitro studies on the motility of fluorophore‐labeled actin filaments along myosin II. Actin filaments were densely labeled with carbocyanine fluorophores, and the gliding velocity adjusted by the concentration of ATP. At imaging frame rates of ～100 Hz, only 100 consecutive frames are sufficient to generate a single high‐resolution image of moving actin filaments with a lateral resolution of ～30 nm. A video‐like sequence is generated from individual reconstructed images by additionally applying a sliding window algorithm. We measured velocities of individual actin filaments of up to ～0.18 μm s^?1, observed strong bending and disruption of filaments as well as locally immobile fragments.     

A New kHz Velocity Map Ion/Electron Imaging Spectrometer for Femtosecond Time-Resolved Molecular Reaction Dynamics Studies

A new velocity map imaging spectrometer is constructed for molecular reaction dynamics studies using time-resolved photoelectron/ion spectroscopy method.By combining a kHz pulsed valve and an ICCD camera,this velocity map imaging spectrometer can be run at a repetition rate of 1 kHz,totally compatible with the fs Ti:Sapphire laser system,facilitating time-resolved studies in gas phase which are usually time-consuming.Time-resolved velocity map imaging study of NH₃ photodissociation at 200 nm was performed and the time-resolved total kinetic energy release spectrum of H+NH₂ products provides rich information about the dissociation dynamics of NH₃.These results show that this new apparatus is a powerful tool for investigating the molecular reaction dynamics using time-resolved methods.     

A general chemical shift decomposition method for hyperpolarized 13C metabolite magnetic resonance imaging

Metabolic imaging with hyperpolarized carbon‐13 allows sequential steps of metabolism to be detected in vivo. Potential applications in cancer, brain, muscular, myocardial, and hepatic metabolism suggest that clinical applications could be readily developed. A primary concern in imaging hyperpolarized nuclei is the irreversible decay of the enhanced magnetization back to thermal equilibrium. Multiple methods for rapid imaging of hyperpolarized substrates and their products have been proposed with a multi‐point Dixon method distinguishing itself as a robust protocol for imaging [1‐¹³C]pyruvate. We describe here a generalized chemical shift decomposition method that incorporates a single‐shot spiral imaging sequence plus a spectroscopic sequence to retain as much spin polarization as possible while allowing detection of metabolites that have a wide range of chemical shift values. The new method is demonstrated for hyperpolarized [1‐¹³C]pyruvate, [1‐¹³C]acetoacetate, and [2‐¹³C]dihydroxyacetone. Copyright © 2016 John Wiley & Sons, Ltd.     

MRI Thermometry Based on Encapsulated Hyperpolarized Xenon

A new approach to MRI thermometry using encapsulated hyperpolarized xenon is demonstrated. The method is based on the temperature dependent chemical shift of hyperpolarized xenon in a cryptophane‐A cage. This shift is linear with a slope of 0.29 ppm °C^?1 which is perceptibly higher than the shift of the proton resonance frequency of water (ca. 0.01 ppm °C^?1) that is currently used for MRI thermometry. Using spectroscopic imaging techniques, we collected temperature maps of a phantom sample that could discriminate by direct NMR detection between temperature differences of 0.1 °C at a sensor concentration of 150 μM . Alternatively, the xenon‐in‐cage chemical shift was determined by indirect detection using saturation transfer techniques (Hyper‐CEST) that allow detection of nanomolar agent concentrations. Thermometry based on hyperpolarized xenon sensors improves the accuracy of currently available MRI thermometry methods, potentially giving rise to biomedical applications of biosensors functionalized for binding to specific target molecules.     

Water‐in‐oil Emulsions Stabilized by Hydrophobized Microfibrillated Cellulose

The properties of water‐in‐toluene emulsions stabilized solely by hydrophobized microfibrillated cellulose (MFC) were investigated. By varying the degree of surface substitution (DSS), the wettability of the MFC was altered. All emulsions prepared with MFC displayed excellent stability to coalescence. The stability to gravity‐induced sedimentation increased with increasing MFC concentration, the highest stability being obtained with MFC of moderate hydrophobicity. Drop sizes increased with increasing DSS, with a corresponding decrease in stability to sedimentation. An increase in the toluene:water ratio at constant MFC concentration resulted in a decrease in the average drop size. For all emulsions, the polydispersity in drop size decreased with decreasing average drop diameter.     

The use of acetone as a substitute for acetonitrile in analysis of peptides by liquid chromatography/electrospray ionization mass spectrometry

The recent worldwide shortage of acetonitrile has prompted interest in alternative solvents for liquid chromatography/mass spectrometry (LC/MS). In this work, acetone was substituted for acetonitrile in the separation of a peptide mixture by reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and in the positive electrospray ionization mass spectrometry (ESI‐MS) of individual peptides. On both C12 and C18 stationary phases, the substitution of acetone for acetonitrile as the organic component of the mobile phase did not alter the gradient elution order of a five‐peptide retention standard, but did increase peak width, shorten retention times, and increase peak tailing. Positive ESI mass spectra were obtained for angiotensin I, bradykinin, [Leu⁵]‐enkephalin, and somatostatin 14 dissolved in both acetonitrile/water/formic acid (25%/75%/0.1%) and acetone/water/formic acid (25%/75%/0.1%). Under optimized ESI‐MS conditions, the mass spectral response of [Leu⁵]‐enkephalin was increased two‐fold when the solvent contained acetone. The substitution of acetone for acetonitrile resulted in only slight changes in the responses of the remaining peptides. A higher capillary voltage was required for optimum response when acetone was used. Compared with acetonitrile/water/formic acid (50/50/0.1%), more interfering species below m/z = 140 were found in the ESI‐MS spectra of acetone/water/formic acid (50/50/0.1%). Copyright © 2009 John Wiley & Sons, Ltd.     

β‐Methylumbelliferone Surface Modification and Permeability Investigations at PENTEL™ Graphite Electrodes

Electrochemical and micro‐imaging analysis of a commercial graphite‐composite material is presented following electro‐oxidation with β‐methylumbelliferone. Charge‐transfer surface modification was observed for the graphite electrode, presumed to have arisen from adsorbed interfacial umbelliferone moieties. The molecular permeability of the new surface towards a range of similar, yet size‐variable (23 ų–136 ų) molecular redox probes is discussed. Red‐shift fluorescence in confocal microscopy offers further support for the presence of a surface‐bound umbelliferone layer. An SEM‐platinum profiling technique was used as an imaging tool to map the umbelliferone surface and size‐distribution of electro‐active sites.     

Facile fabrication of a superhydrophobic surface from natural Eucommia rubber

In this study, we introduce a fabrication method for a superhydrophobic surface made from natural Eucommia rubber. Based on the Eucommia rubber extract solution, we prepared a type of superhydrophobic material using the simple phase separation method and the addition of a low‐surface‐energy substance method, thus developing a new approach for the application of natural Eucommia rubber. The experimental results showed that a superhydrophobic film could be obtained by both the addition of acetone and induction by water vapor. Additionally, the film exhibited properties closely related to the crystalline Eucommia rubber spherical particles with a hierarchical structure. The addition of hydrophobic silica also increased the hydrophobic property of the Eucommia rubber film. When the content of the silica was 4% (wt%), the contact angle of the composite film reached 160.7°, which could be attributed to the properties of the nano‐silica and the micro‐nano structure of the composites. Copyright © 2017 John Wiley & Sons, Ltd.