真35断块储层渗透率与KY聚合物相对分子质量的匹配性研究

为了筛选适合真35断块储层的KY系列聚合物,测定了岩心的气/液(汞)测渗透率、孔隙度及KY系列聚合-物在地层条件下的水动力学半径,建立了真35-6井岩心气测渗透率Kg、平均孔喉半径R及KY系列聚合物相对分-子质量M、聚合物在江苏油田真35断块的地层水中分子水动力学半径Rh之间的关联性,在此基础上根据1/3架桥-堵塞理论获得满足驱替要求的KY系列聚合物相对分子质量与岩心气测渗透率Kg的关系R=0.026Kg+0.2071。研究结果表明,真35储层的气测渗透率与平均孔喉半径成线性相关的关系,KY系列聚合物的水动力学半径与其--相对分子质量存在对数相关关系(R=0.1212ln M0.6831)。真35断块实施KY聚合物驱时储层气测渗透率与KY-系列聚合物相对分子质量应满足的匹配关系为:M<615e0.01Kg。即KY聚合物的相对分子质量应不超过此上限,从而可以避免因选择相对分子质量过大的聚合物而导致的油层堵塞。

亲水性高分子对冰重结晶的抑制作用研究

研究了聚丙烯酸、聚丙烯胺、聚乙烯醇三种亲水性高分子对冰重结晶过程的影响。结果表明,随着溶液浓度的增加,三种高分子对冰重结晶的抑制作用均逐渐增强。不同侧链基团会影响高分子对冰重结晶过程的调控效果,聚丙烯胺和聚丙烯酸没有明显抑制冰重结晶的效果,而聚乙烯醇具有很强的抑制冰重结晶的能力。对不同醇解度的聚乙烯醇研究发现,聚乙烯醇抑制冰重结晶的效果会随着醇解度的提高而不断增强。通过研究水分子的质子自旋-自旋弛豫时间(T2)发现:高羟基含量的聚乙烯醇可以更加有效地限制水的扩散运动,从而抑制冰重结晶。

Molecular Dynamics Study on Microstructure of Potassium Dihydrogen Phosphates Solution

Molecular dynamics simulations were carried out to study the internal energy and microstructure of potassium dihydrogen phosphates （KDP） solution at different temperatures. The water molecule was treated as a simple-point-charge model, while a seven-site model for the dihydrogen phosphate ion was adopted. The internal energy functions and the radial distribution functions of the solution were studied in detail. An unusually large local particle number density fluctuation was observed in the system at saturation temperature. It has been found that the specific heat of oversaturated solution is higher than that of unsaturated solution, which indicates the solution experiences a crystallization process below saturation temperature. The radial distribution function between the oxygen atom of water and the hydrogen atom of the dihydrogen phosphate ion shows a very strong hydrogen bond structure. There are strong interactions between potassium cation and oxygen atom of dihydrogen phosphate ion in KDP solution, and much more ion pairs were formed in saturated solution.

New Hexagonal-rhombic Trilayer Ice Structure Confined between Hydrophobic Plates

We perform molecular dynamics simulations for water confined between two smooth hydrophobic walls and observe two crystalline structures with one being first reported. Both of these structures obey the ice rule. The novel ice phase is a flat hexagonal-rhombic trilayer ice, obtained under 1 GPa load at wall separation of 1.0 nm. In this structure, the water molecules in the two layers next to one of the walls （outer layers） and in the middle layer form hexagonal rings and rhombic rings, respectively. For a molecule in the outer layers, three of its four hydrogen bonds are in the same layer, and the other one hydrogen bond connects to the middle layer. For a molecule in the middle layer, only two of its four hydrogen-bonds are located in the same layer, and the other two connect to two different outer layers. Despite their different motifs, the area densities of the three layers are almost equal. The other structure is a flat hexagonal bilayer ice produced at wall separation of 0.8 nm under lateral pressure of 100 MPa, analogous to a system demonstrated by Koga et al [Phys. Rev. Lett. 79, 5262 （1997）]. Both first-order and continuous phase transitions take place in these simulations.

Effects of Solvent Molecules on the Interlayer Spacing of Graphene Oxide

Graphene oxide （GO） contains numerous functional groups that facilitate the intercalation of polar solvents. The properties and applications of GO are closely related to its interlayer spacing. We report on the changes in the interlayer spacing of GO after the adsorption of water molecules and the polar organic solvents C2H602 （EG）, C3HTNO （DMF）, C5H9NO （NMP）. Experiments were conducted to investigate the variations in the functional groups and structure of GO after solvent adsorp-tion, and they play a vital role in modeling and verifying the results of molecular dynamics simulation. The most stable GO structures are obtained through molecular dynamics simulation. The expansion of the interlayer spacing of GO after the adsorption of monolayer solvent molecules corresponds to the minimum three-dimensional size of the solvent molecules. The spatial arrangement of solvent molecules also contributes to the changes in interlayer spacing. Most adsorbed molecules are oriented parallel to the carbon plane of GO. However, as additional molecules are adsorbed into the interlaminations of GO, the adsorbed molecules are oriented perpendicular to the carbon plane of GO, and a large space forms between two GO interlayers. In addition, the role of large molecules in increasing interlayer spacing becomes more crucial than that of water molecules in the adsorption of binary solvent systems by GO.

Kinetic-Thermodynamic Analysis of the Reactive Distillation Process of the Cyclohexene Hydration Using the Zeolite Catalyst

Reactive distillation could be utilized to produce cyclohexanol through the cyclohexene hydration. By means of highly active zeolite catalyst HZSM-5, the kinetic-thermodynamic analysis of this reactive distillation has been carried out to get the characteristics of the reactive distillation. Results from kinetic and thermodynamic analysis indicate that the optimal pressure of this reactive distillation process should be set to higher pressure such as 0.3 or 0.4 MPa. To avoid the recovery of cyclohexanol at the top of the column, an unreactive section should be allocated at the upper column. In addition, the inert component benzene is more unfavorable to the reactive distillation process in comparison with the inert cyclohexane.

Electron transfer kinetics in CdS/Pt heterojunction photocatalyst during water splitting

Noble metal cocatalysts have shown great potential in boosting the performance of CdS in photocatalytic water splitting.However,the mechanism and kinetics of electron transfer in noble-metal-decorated CdS during practical hydrogen evolution is not clearly elucidated.Herein,Pt-nanoparticle-decorated CdS nanorods(CdS/Pt)are utilized as the model system to analyze the electron transfer kinetics in CdS/Pt heterojunction.Through femtosecond transient absorption spectroscopy,three dominating exciton quenching pathways are observed and assigned to the trapping of photogenerated electrons at shallow states,recombination of free electrons and trapped holes,and radiative recombination of locally photogenerated electron-hole pairs.The introduction of Pt cocatalyst can release the electrons trapped at the shallow states and construct an ultrafast electron transfer tunnel at the CdS/Pt interface.When CdS/Pt is dispersed in acetonitrile,the lifetime and rate for interfacial electron transfer are respectively calculated to be~5.5 ps and~3.5×10^(10) s^(−1).The CdS/Pt is again dispersed in water to simulate photocatalytic water splitting.The lifetime of the interfacial electron transfer decreases to~5.1 ps and the electron transfer rate increases to~4.9×10^(10) s^(−1),confirming that Pt nanoparticles serve as the main active sites of hydrogen evolution.This work reveals the role of Pt cocatalysts in enhancing the photocatalytic performance of CdS from the perspective of electron transfer kinetics.

Molecular Dynamics Investigation of Benzene in Supercritical Water

Microscopic structure and diffusion properties of benzene in ambient water (298 K, 0.1 MPa) and super critical water (673－773 K, 25－35 MPa) are investigated by molecular dynamics simulation with site-site models. It is found that at the ambient condition, the water molecules surrounding a benzene molecule form a hydrogen bond network. The hydrogen bond interaction between supercritical water molecules decreases dramatically under supercritical conditions. The diffusion coefficients of both the solute molecule and solvent molecule at supercritical conditions increase by 30－180 times than those at the ambient condition. With the temperature approaching the critical temperature, the change of diffusion coefficient with pressure becomes pronounced.

A molecular dynamics study of calcium silicate hydrates-aggregate interfacial interactions and influence of moisture

The interface properties between hydrated cement paste(hcp)and aggregates largely determine the various performances of concrete.In this work,molecular dynamics simulations were employed to explore the atomistic interaction mechanisms between the commonly used aggregate phase calcite/silica and calcium silicate hydrates(C-S-H),as well as the effect of moisture.The results suggest that the C-S-H/calcite interface is relatively strong and stable under both dry and moist conditions,which is caused by the high-strength interfacial connections formed between calcium ions from calcite and high-polarity non-bridging oxygen atoms from the C-S-H surface.Silica can be also adsorbed on the dry C-S-H surface by the H-bonds;however,the presence of water molecules on the interface may substantially decrease the affinities.Furthermore,the dynamics interface separation tests of C-S-H/aggregates were also implemented by molecular dynamics.The shape of the calculated stress-separation distance curves obeys the quasi-static cohesive law obtained experimentally.The moisture conditions and strain rates were found to affect the separation process of C-S-H/silica.A wetter interface and smaller loading rate may lead to a lower adhesion strength.The mechanisms interpreted here may shed new lights on the understandings of hcp/aggregate interactions at a nano-length scale and creation of high performance cementitious materials.

Orientation and Motion of Water Molecules at Air/Water Interface

Here we report a quantitative study of the orientational structure and motion of water molecule at the air/water interface. Analysis of Sum Frequency Generation （SFG） vibrational peak of the free O-H stretching band at 3700 cm^-1 in four experimental configurations showed that orientational motion of water molecule at air/water interface is libratory within a limited angular range. The free OH bond of the interracial water molecule is tilted around 33°from the interface normal and the orientational distribution or motion width is less than 15°. This picture is significantly different from the previous conclusion that the interracial water molecule orientation varies over a broad range within the ultrafast vibrational relaxation time, the only direct experimental study concluded for ultrafast and broad orient, ational motion of a liquid interface by Wei et al. （Phys. Rev. Lett. 86, 4799, （2001）） using single SFG experimental configuration.

Molecular dynamics simulation of water transport through graphene-based nanopores: Flow behavior and structure characteristics

The flow behavior of pressure-driven water infiltration through graphene-based slit nanopores has been studied by molecular simulation.The simulated flow rate is close to the experimental values,which demonstrates the reasonability of simulation results.Water molecules can spontaneously infiltrate into the nanopores,but an external driving force is generally required to pass through the whole pores.The exit of nanopore has a large obstruction on the water effusion.The flow velocity within the graphene nanochannels does not display monotonous dependence upon the pore width,indicating that the flow is related to the microscopic structures of water confined in the nanopores.Extensive structures of confined water are characterized in order to understand the flow behavior.This simulation improves the understanding of graphene-based nanofluidics,which helps in developing a new type of membrane separation technique.

Dynamic Simulation on Surface Hydration and Dehydration of Monoclinic Zirconia

The commonly used oxide-supported metal catalysts are usually prepared in aqueous phase,which then often need to undergo calcination before usage.Therefore,the surface hydration and dehydration of oxide supports are critical for the realistic modeling of supported metal catalysts.In this work,by ab initio molecular dynamics(AIMD)simulations,the initial anhydrous monoclinic ZrO_(2)(111)surfaces are evaluated within explicit solvents in aqueous phase at mild temperatures.During the simulations,all the two-fold-coordinated O sites will soon be protonated to form the acidic hydroxyls(HO_(L)),remaining the basic hydroxyls(HO^(∗))on Zr.The basic hydroxyls(HO^(∗))can easily diffuse on surfaces via the active proton exchange with the undissociated adsorption water(H_(2)O^(∗)).Within the temperatures ranging from 273 K to 373 K,in aqueous phase a certain representative equilibrium hydrated m-ZrO_(2)(¯111)surface is obtained with the coverage(θ)of 0.75 on surface Zr atoms.Later,free energies on the stepwise surface water desorption are calculated by density functional theory to mimic the surface dehydration under the mild calcination temperatures lower than 800 K.By obtaining the phase diagrams of surface dehydration,the representative partially hydrated m-ZrO_(2)(111)surfaces(0.25≤θ<0.75)at various calcination temperatures are illustrated.These hydrated m-ZrO_(2)(111)surfaces can be crucial and readily applied for more realistic modeling of ZrO_(2) catalysts and ZrO_(2)-supported metal catalysts.

Fabrication of Super Hydrophobic Surfaces on Copper by Solution-immersion

Super hydrophobic copper wafer was prepared by means of solution immersion and surface self-assembly methods. Different immersion conditions were explored for the best hydrophobic surface. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and water contact angle measurements were used to investigate the morphologies, microstructures, chemical compositions and hydrophobicity of the produced films on copper substrates, respectively. Results show that the super hydrophobic surface is composed of micro structure of Cu 7 S 4 . The films present a high water contact angle larger than 150°, a low sliding angle less than 3°, good abrasion resistance and storage stability. The molecular dynamics simulation confirms that N-dodecyl mercaptan molecules link up with Cu 7 S 4 admirably, compared with Cu, which contributes to the stable super hydrophobic surface.

Vibrating Carbon Nanotubes as Water Pumps

Nanopumps conducting fluids directionally through nanopores and nanochannels have attracted considerable interest for their potential applications in nanofiltration, water purification, and hydroelectric power generation Here, we demonstrate by molecular dynamics simulations that an excited vibrating carbon nanotube （CNT） cantilever can act as an efficient and simple nanopump. Water molecules inside the vibrating cantilever are driven by centrifugal forces and can undergo a continuous flow from the fixed to free ends of the CNT. Further extensive simulations show that the pumping function holds good not only for a single-file water chain in a narrow （6,6） CNT, but also for bulk-like water columns inside wider CNTs, and that the water flux increases monotonically with increasing diameter of the nanotube.

Dissipative particle dynamics thermostat: a novel thermostat for molecular dynamics simulation of liquid crystals with Gay–Berne potential

The Gay-Berne （GB） model has been proved to be highly successful in the simulation of liquid crystal phases via both molec- ular dynamics （MD） and nonequilibrium molecular dynamics （NEMD）. However, the conventional thermostats used in the simulations of GB systems, such as Nose-Hoover and Langevin thermostats, have serious shortcomings especially in NEMD simulations. Recently, dissipative particle dynamics （DPD） has established itself as a useful thermostat for soft matter simulations, whereas the application of DPD thermostat in （NE）MD simulations is limited to the spherically isotropic potential models, such as the Lennard-Jones model. Considering the virtues of the DPD thermostat, that is, local, momentum conserved, and Galilean invariant, we extend the DPD thermostat to the non-spherical GB model. It is interesting to find that the translational DPD and rotational DPD thermostats can be used in the GB system independently and both can achieve the thermostatting effects. Also, we compared the performance of the DPD thermostat with other commonly used thermostats in NEMD simulations by investigating the streaming velocity profiles and the dynamics of phase separation in a typical but simple binary GB mixture under shear field. It is revealed that the known virtues of DPD thermostats, such as Galilean invariant, shear velocity profile-unbiased, and unscreened hydrodynamic interactions, are still intact when applying to GB systems. Finally, the appro- priate parameters for the DPD thermostat in the GB system are identified for future investigations.

Simulating ion clustering in potassium thiocyanate aqueous solutions with various ion-water models

Using a molecular dynamics simulation technique,we compared several commonly used ion-water models to describe the microscopic structures and dynamics in KSCN aqueous solutions.Results are compared with observations of femtosecond infrared vibrational-energy transfer and anisotropy measurements.The Jorgensen/TIP4P model is found to provide the best reproduction of clustering properties such as percentage of clustered ions,cluster-size distribution,concentration dependence of the water,and ion-rotation time constants.

Structural properties of hydroxyl-substituted alkyl benzenesulfonates at the water/vapor and water/decane interfaces

Molecular dynamics simulations have been performed to investigate the structural properties of hydroxyl-substituted alkyl benzenesulfonate monolayers formed at the water/vapor and water/decane interfaces.We report a detailed study of the interfacial properties-liquid density profile,hydrogen bond structure,surfactant aggregate structure and order parameter-of the novel anionic surfactant,sodium 2-hydroxy-3-decyl-5-octylbenzenesulfonate(C10C8OHphSO3Na).Simulation results show that:with increasing number of surfactant molecules,the average number of intramolecular hydrogen bonds per surfactant molecule in the monolayer decreases,but the structures forming the intramolecular hydrogen bonds still play a dominant role;the hydrophobic part of the alkyl tail chain,especially the decyl substituent on the third carbon atom in the benzene ring,becomes straighter,and more ordered towards the external interface at higher surfactant coverage;two-dimensional radial distribution functions can describe the characteristic of surfactant aggregate structures and highlight the decane phase effect on the orientation of the hydrophobic part of the surfactant;the surfactant molecules readily form long-range hydrogen bonded structures.Our results are an important complement to experimental studies.We used the all-atom model by employing the GROMACS and ffAMBER programs in the simulations,which provides a new way to simulate the interfacial behavior of alkyl benzenesulfonate surfactants.

Crystal-oriented wrinkles with origami-type junctions in few-layer hexagonal boron nitride

Understanding layer interplay is the key to utilizing layered heterostructures formed by the stacking of different two-dimensional materials for device applications. Boron nitride has been demonstrated to be an ideal substrate on which to build graphene devices with improved mobilities. Here we present studies on the morphology and optical response of annealed few-layer hexagonal boron nitride flakes deposited on a silicon substrate that reveal the formation of linear wrinkles along well-defined crystallographic directions. The wrinkles formed a network of primarily threefold and occasionally fourfold origami-type junctions throughout the sample, and all threefold junctions and wrinkles formed along the armchair crystallographic direction. Furthermore, molecular dynamics simulations yielded, through spontaneous symmetry breaking, wrinkle junction morphologies that are consistent with both the experimental results and the proposed origami-folding model. Our findings indicate that this morphology may be a general feature of several two-dimensional materials under proper stress-strain conditions, resulting in direct consequences in device strain engineering.

STOCHASTIC SYNCHRONIZATION OF CIRCADIAN RHYTHMS

Models of circadian genetic oscillators involving interlinked feedback processes in molecular level genetic networks in Drosophila melanogaster and Neurospora crassa are studied, and mechanisms whereby synchronization can arise in an assembly of cells are examined. The individual subcellular circadian oscillatory processes are stochastic in nature due to the small numbers of molecules that are involved, and are subject to large fluctuations. The authors investigate and present the simulations of the stochastic dynamics of ensembles of clock-regulating proteins in different nuclei that communicate via ancillary small molecules, environmental parameters, additive cellular noise, or through diffusive processes. The results show that the emergence of collective oscillations is a macroscopic observable which has its origins in the microscopic coupling between distinct cellular oscillators.

Molecular Mechanism of the Early Stage of Amyloidogenic Hexapeptides(NFGAIL) Aggregation

Peptides/proteins aggregation can give rise to pathological conditions of many human diseases.Small partially ordered oligomers formed in the early stage of aggregation,rather than mature fibrils,are thought to be the main toxicity agent for the living cell.Thus,understanding the pathway and the underlying physical mechanism in the early stage of aggregation is very important for prevention and treatment of these protein functional diseases.Herein we use all-atom molecular dynamics simulations to study the aggregation of four NFGAIL hexapeptides(NFGAIL peptide is a core segment of human islet amyloid polypeptide and exhibits similar aggregation kinetics as the full-length polypeptide).We observe that the peptide monomers in water mainly adopt non-structural coil configurations;the four peptides which are randomly placed in water aggregate spontaneously to partially ordered oligomer(β-sheets)through dimerization or trimerization,with the dimerization predominated.Both parallel and anti-parallelβ-sheets are observed.The hydrophobic interactions drive the initial peptides associations,and the subsequent conformational fluctuations promote the formation of more hydrogen bonds between the dangling hydrogen sites in the main chains of peptides.