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Fluid saturation plays an important role in rock weakening. However, few researches reveal the controlling factor(s) behind the rock weakening particularly from geochemical perspective. We performed rock failure/fracture reactivation tests on dry and wet samples (saturated with high/low salinity brine). We examined the effect of fluid saturation and salinity on rock mechanical properties through a unique triaxial compression system with combination of micro-seismicity monitoring. Besides, the induced time-dependent micro-seismicity events were located to characterize the fracture orientation together with medical CT imaging. Moreover, we performed geochemical modelling to link the surface energy to rock mechanics from geochemical perspective.Our results show that the peak stress of saturated samples is 11.7% to 15.0% less than unsaturated samples, confirming that fluid saturation can weaken rock. Lowering salinity appears to play a negligible role in the reduction of elastic modulus and peak stress of intact sandstones. We also did not observe the expansion of micro-seismicity cloud along main fracture plane, suggesting that lowering salinity may not trigger micro-fracture generation under confining condition. However, sample saturated with low salinity brine shows a much slower increase rate of differential stress during the plastic deformation to reach yield point during fracture reactivation process compared to the sample saturated with high salinity brine. This work contributes to the existing knowledge of rock weakening by providing quantitative geochemical characterization with implications in water-assisted enhancing hydrocarbon recovery and CO2 geological storage.

Objectives/Scope Underground hydrogen storage (UHS) has been raising more interest to safely and cost-effectively store hydrogen at large-scale to help the transition from fossil fuel to sustainable energy and to achieve net-zero emission target. During hydrogen subsurface storage particularly in depleted gas reservoirs, the wellbore plays an important role in injection and reproduction to meet seasonal energy demand. However, it is still unclear how wellbore cement would react with stored hydrogen in the presence of formation brine, which may effect long-term cement integrity. We thus performed thermodynamic modelling on cement reactions with hydrogen and water at reservoirs conditions. Methods, Procedures, Process The dissolution of individual components of cement including C3S, C2S, C3A, C4AF and gypsum of Class G/H, and potential precipitation of twenty secondary minerals were simulated at an infinite time scale at reservoir temperature and pressure (representing the worst case scenario of cement degradation from geochemical perspective; in real case, the degree of cement degradation would be much less than the results from thermodynamic modelling as it is a time-dependent process). The extent of cement mineral reactions with hydrogen was compared with that of methane and carbon dioxide to assess the wellbore cement integrity during UHS compared to UGS and CCS. Results, Observations, Conclusions The cement hydration process would lead to the transformation of the major cement compositions C3S and C2S to C1.5SH (CSH) and portlandite. Adding hydrogen would only slightly change the percentage of C1.5SH and portlandite and generate a small fraction of new mineral mackinawite. As a comparison, adding methane would generate a considerable amount of calcite. When CO2 is involved, all CSH compounds would transform to calcite through the cement carbonation process. Overall, the compositional mineral phases of cement after cement hydration is more closed to the case involving H2 compared to CH4 and CO2, implying a relatively low risk of wellbore cement degradation during UHS. Novel/Additive Information Our work underlines the importance of incorporating geochemical modelling in hydrogen geo-storage evaluation when using existing old wells and new drilled wells.

There has been a “trade-off” between ion exchange capacity (IEC) and mechanical properties in anion exchange membranes. Thinking out of the box, high ion conductivity was realized with only a small...

Hydraulic fracturing has been widely implemented to enhance hydrocarbon production from shale reservoirs. However, one of the main challenges during hydraulic fracturing is to understand what factor(s) triggers high salinity of flowback water, which sometimes can be up to 300,000 mg/L. While several mechanisms have been proposed to explain the controlling factor behind the high salinity of flowback water, there has been little discussion about the effect of fluid-shale interactions (e.g., mineral dissolution and surface complexation) on the high salinity, and far too attention has been paid to quantify the contribution of fluid-shale interactions. We thus conducted spontaneous imbibition experiments using deionised water and outcrops from Marcellus, Barnett and Eagle Ford shale plays with minor in-situ precipitated salts. We also monitored the pH, electrical conductivity and ion concentrations (Cl-, K+, Ca2+, NO3-, F-, Br- and NH+) of the surrounding water during spontaneous imbibition process in consecut...

The transition of energy from fossil fuels to renewable energy particularly hydrogen is becoming the centre of decarbonization and roadmap to achieve net-zero carbon emission. To meet the requirement of large-scale hydrogen storage as a key part of hydrogen supply chain, underground hydrogen storage can be the ultimate solution to economically store hydrogen thus meet global energy demand. Compared to other types of subsurface storage sites such as salt caverns and aquifers which are limited to geographical locations, depleted gas reservoirs have been raising more interest because of the wider distribution and higher storage capacity. However, safely storing and cycling of hydrogen in depleted gas reservoirs requires caprock, reservoir and wellbore to remain high stability and integrity. Nevertheless, current research on storage integrity during underground hydrogen in depleted gas reservoirs is still scarce and non-systemic. We therefore reviewed the major challenges on storage integrity associated with geochemical reactions, microbial activities, faults and fractures and hydrogen cycling perspectives. The processes and impacts of abiotic and biotic mineral dissolution/precipitation, faults and fracture reactivation and propagation in caprock and host-rock, wellbore instability due to cement degradation and casing corrosion, stress change during hydrogen cycling, etc. on storage integrity were comprehensive reviewed and analysed. Furthermore, a technical screening tool with consideration of controlling variables, risks and consequences on storage integrity was developed to identify the potential risks associated with storage integrity. Lastly, knowledge gaps together with feasible methods and pathways have been identified to mitigate the risks and thus enables large-scale underground hydrogen storage.

For high-performance anion exchange membrane fuel cells (AEMFCs), the anion exchange membrane (AEMs) should be as thin as possible to reduce the ohmic resistance. However, the mechanical stability of ultrathin AEMs cannot be guaranteed, as well as a huge risk of gas (H

The wettability of shale oil reservoirs is an important petrophysical property to determine subsurface multiphase flow and residual oil saturation. While a few studies have been undertaken to under...

Hydraulic fracturing technique is of vital importance to increase fuel energy, in particular to unlock the unconventional resources (e.g., tight oil, shale oil and shale gas reservoirs). However, low recovery of hydraulic fracturing fluid has been in the centre of attention from both technical and environmental perspectives in the last decade. To gain a deeper understanding of controlling factor(s) over low recovery of hydraulic fracturing fluids, we hypothesized that hydraulic fracturing fluid (usually low salinity water) increases hydrophilicity of reservoir rocks, thus stress intensity factor, which in return facilitates in-situ micro-fractures extension. To test this hypothesis, we developed a physical model with consideration of capillary pressure which is associated with wettability. Moreover, we calculated stress intensity factor using our previous contact angle results with presence of low salinity and high salinity water [Xie et al., The low salinity effect at high temperatures, Fuel, 200 (2017) 419–426]. Furthermore, we examined the effect of tip width of in-situ micro-fractures, distance from main hydraulic fractures on micro-fractures extension at different wetting systems. Our results demonstrate that low salinity water indeed increases stress intensity factor as compared to high salinity water due to the wettability alteration. Our results also show that the length of micro-fracture extension increases up to 15 times than the original micro-fracture length due to the wettability alteration when the tip width of in-situ micro-fracture reaches 10 nm. This likely explains the extension of micro-fractures due to water uptake by shale. Moreover, micro-fracture extension is more pronounced for micro-fractures located nearby a wellbore, suggesting that a huge amount of hydraulic fluids likely remains at the vicinity of the wellbore. Knowing wettability thus stress intensity factor, the disappearance of hydraulic fracturing fluids and EOR potential in tight sandstone and shale reservoirs can therefore be quantified.

Megalitres of water with associated dissolved oxygen are injected into shale reservoirs during the hydraulic fracturing process. Pyrite oxidation, if it occurs in-situ, can generate extra H+, thereby dissolving calcite and increasing the salinity of flowback water. The process of calcite dissolution may soften the hydraulic fracture surfaces, resulting in proppants embedment and thus decreasing fracture conductivity for calcite-rich shales. Therefore, it is of vital importance to understand the impact of in-situ pyrite oxidation on fluid-shale interactions, particularly calcite dissolution, to help industry screen and design hydraulic fracturing fluids in shales. Spontaneous imbibition experiments were performed using Marcellus shale samples under three conditions: i) ambient conditions, where the fluid was in equilibrium with atmospheric air throughout the tests, ii) limited O2 condition, where the fluid was free equilibrated with air in a sealed cylinder and iii) vacuum condition, where the fluid in a sealed cylinder was degassed. The pH and ion concentrations were measured upon completion of the experiments. To further explore how pyrite oxidation affects fluid-rock interactions, we performed geochemical simulations with considerations of mineral dissolution (calcite, albite, quartz, chalcopyrite, pyrite and dolomite), surface complexation and the dissolved O2 on fluid salinity. The spontaneous imbibition tests show that the salinity of fluids in ambient conditions is higher than the limited or vacuumed saturation fluids, confirming that pyrite oxidation generates H+ which would dissolve minerals such as calcite and dolomite. This result is also supported by the observed pH and the concentration of dissolved Ca2+. The fluid fully saturated with O2 has the lowest pH and highest Ca2+ compared to limited O2 saturation condition and degassed condition. Scanning electron microscopy analyses show that brine saturation barely affects the morphology and elemental distribution of pyrite at ambient conditions, suggesting that pyrite oxidation plays a minor role in fluid salinity. Geochemical modelling also indicates that although pyrite oxidation can slightly increase fluid salinity, the salinity increment is less than 5% of reported flowback water salinity, confirming that the dissolved O2 in hydraulic fracturing fluids has a minor effect on fluid-rock interaction thus the salinity increment. This work demonstrates that pyrite dissolution at lab-scale would overestimate the impact of fluid-shale interactions and calcite dissolution in reservoir conditions. We prove that pyrite dissolution in in-situ conditions results in minor implications for fluid-shale interactions and calcite dissolution. Consequently, we limit intrinsic uncertainty of hydraulic fluid design associated with pyrite oxidization especially for calcite-rich shales.

The microseismicity associated with hydraulic fracturing in unconventional reservoir (i.e. shale gas play) has been investigated in the past several decades. Few experimental studies with respect to the focal mechanism and stress inversion was conducted, especially for Glutenite reservoir. In this study, the glutenite core was taken from the underground of 2600 m. Next, we performed scaled hydraulic fracturing tests on the cubic core (50×50×50mm) under geological principle stress condition in true tri-axial stress cell. Meanwhile, we monitored wellbore and pore pressure, and micro-seismic events during the fracture propagation from six faces of the cubic rock. Micro-seismic survey and events were interpreted to identify the induced fractures distribution in three dimension. Source mechanism and stress inversion were analyzed by moment tensor decomposition. The correlation of failure plane from microseismicity and tested sample implied that the microseismic events were accurately localized. The distribution of microseismic events from secondary and reopening tests indicated that the hydraulic fracturing induced microseismicity are mainly caused by significant tip effect (i.e. reactivate preexisting natural fractures). Based on source mechanism analysis, we found that the most of the failure are dominated by double-couple (DC). The correlation between original principle stress state and the one from STESI inversion indicated that the direction of principle stresses, especially for σ2 and σ3 inversed from reopening test, can be highly influenced by the hydraulic induced fracture or weak planes during secondary fracturing test.

A high-performance anion exchange membrane (AEM) is critical for the development of alkaline fuel cell. In this work, AEMs with an interpenetrating polymer network (IPN) are synthesized. An electron microscope clearly reveals a highly efficient “ion channel” network, which is constructed with a small amount of cation exchange groups. This specially designed ion channel leads to extraordinary hydroxide conductivity (e.g., 257.8 mS cm -1 at 80 °C) of IPN AEMs at moderate ion exchange capacity ( IEC = 1.75 mmol g − 1 ), as well as excellent long-term alkaline stability at harsh condition which showed that 81% of original conductivity can be retained after a long time for 1248 hours. Moreover, a remarkable peak power density of 1.20 W cm -2 (0.1 MPa backpressure) with nonprecious metal (FeNx-CNTs) as oxygen reduction reaction (ORR) catalyst in a fuel cell test was achieved. This work offers a general strategy to prepare high-performance AEMs based on IPN structure design.

This work, using three-dimension proton exchange membrane fuel cell (PEMFC) model combined with theoretical analysis, is mainly to improve the performance of PEMFC through optimizations of fuel cell structure, adding rectangle blockages in the gas channel. Performance comparison, velocity distribution, interface reactant concentration difference, and pressure drop have been studied in the paper. The result shows that, longitudinal vortices would appear and the performance could be improved with the addition of blockages in the gas channel, especially at high current density with closer arrangement. According to field synergy principle, average mass transfer synergy angle could prove the superiority of optimized structure in the ability of mass transfer. Besides, a novel physical quantity, effective mass transfer coefficient, has been proposed. The effective mass transfer coefficient, is the ability of mass transfer in the direction of electrochemical reaction in PEMFC, which could also give mechanism explanation for the performance improvement.

Thermoelectric devices can convert thermal energy directly into electrical energy. The aim of this study was to develop an approach for integrating computer-aided analysis with an optimization method that could be applied to the design and optimization of thermoelectric generators. The optimization framework consisted of a model generator, a direct solver, and a numerical optimizer. The simplified conjugate-gradient method (SCGM) was used to build the optimizer, and the general-purpose finite-element code was used for the direct solver and model generator. This approach was applied to the multi-objective and multi-parameter optimization of geometric thermoelectric generators to design an optimal structure for both a two-stage bismuth-telluride (BiTe)-based and skutterudite-based thermoelectric generator (TEG) module. The leg length and the ratio between the cross-sectional areas (i.e., footprint) of the semiconductor columns and the TEG module were found to significantly affect the TEG performance; hence, all were incorporated into the present optimization study. Multi-objective optimization was used to realize a design that properly balanced the power output and conversion efficiency so that both improved simultaneously.

A channel is a significant part of a proton exchange membrane fuel cell (PEMFC), and the configuration of the channel has a great effect on the mass transfer of the PEMFC, which directly influences the performance. In this study, a three-dimensional, single-phase, and non-isothermal model of a PEMFC with a single straight channel is developed. Based on the model, genetic algorithm (GA) is adopted to obtain an optimal design of the channel configuration. Power consumption of flow and output power of a PEMFC are considered into the objective function, and the width of bottom and top edges of the channel, in both the anode and cathode sides, are selected as variables. The optimal design obtained is a trapezoidal channel. At an operating potential of 0.4 V, the increment in current density in the optimal design is 10.92% compared to a basic design having a square channel. Moreover, the optimal design shows more uniform distributions of reactants and current density than the basic design.

Super-insulating aerogels are promising materials to improve the energy efficiency of buildings. However, fabricating super-insulating yet mechanically robust and shape-memory aerogels remains challenging. Here, we integrate graphene oxide and a block copolymer to fabricate hybrid aerogels with triple networks and systematically study their mechanical and thermal properties. We show that the first network serves as sacrificial bonds and dissipates energy upon deformation, enabling the aerogels to have a high mechanical performance. The second network allows the aerogels to memorize the original permanent shape, and the third network is able to store strain energy and fix the aerogels in a temporary shape by vitrification. Remarkably, the strong phonon-scattering effect generated by the enormous interfaces between the three networks yields an ultra-low solid thermal conductivity of ∼8 mW m−1 K−1. The multi-functionality makes this class of hybrid aerogels particularly suitable for super-insulation applications on complex surfaces and in small spaces of buildings, industry and spacecrafts.

Water uptake induced by fluid&ndash, rock interaction plays a significant role in the recovery of flowback water during hydraulic fracturing. However, the existing accounts fail to fully acknowledge the significance of shale anisotropy on water uptake typically under in situ reservoir temperature. Thus we investigated the shale-hydration anisotropy using two sets of shale samples from the Longmaxi Formation in Sichuan Basin, China, which are designated to imbibe water parallel and perpendicular to shale bedding planes. All the samples were immersed in distilled water for one to five days at 80 &deg, C or 120 &deg, C. Furthermore, samples&rsquo, topographical and elemental variations before and after hydration were quantified using energy-dispersive spectroscopy&ndash, field-emission scanning electron microscopy. Our results show that shale anisotropy and imbibition time strongly affect the width of pre-existing micro-fracture in hydrated samples. For imbibition parallel to lamination, the width of pre-existing micro-fracture initially decreases and leads to crack-healing. Subsequently, the crack surfaces slightly collapse and the micro-fracture width is enlarged. In contrast, imbibition perpendicular to lamination does not generate new micro-fracture. Our results imply that during the flowback process of hydraulic fracturing fluid, the shale permeability parallel to bedding planes likely decreases first then increases, thereby promoting the water uptake.

To reveal the enhanced oil recovery (EOR) potential of CO2 huff-n-puff in fractured tight conglomerate reservoirs, hydraulic fracturing combined with CO2 huff-n-puff experiments were conducted using a true triaxial stress cell core fracturing and displacement system. To better understand the potential mechanisms behind CO2 huff-n-puff, the change in rock properties and formation water properties caused by the interactions among supercritical CO2/formation water/oil/rock were investigated. Experimental results demonstrate that CO2 huff-n-puff is viable to boost oil recovery in tight conglomerate reservoirs with recovery factor of 23.2% after hydraulic fracturing and depletion process. Rock surface morphology, mineralogical composition and formation water composition analysis indicate that supercritical CO2 leads the water-oil-rock system to more water-wet by increasing rock surface roughness. Geochemical simulation results combining the surface complexation and ion-exchange shows that supercritical CO2 weakens the crude oil adsorption on rock surface, which also contributes to the oil recovery increment. These results reveal the EOR feasibility of CO2 huff-n-puff in fractured tight conglomerate reservoirs, and provide insights to characterize geochemical features of carbonated brine/oil/rock.

We reported an interface-induced synthesis of iron nitrogen (FeNx) enriched carbon nanotubes (FeNx-CNTs) with high activity in alkaline and acidic environment for oxygen reduction reaction (ORR) by coating polypyrrole (PPy) thin layers on iron-doped zeolitic imidazolate framework-8 (Fe-ZIF). The constructed polymer/metal-organic framework (MOF) interface suppresses the agglomeration of iron (Fe) atomic sites during the thermal activation, and thus facilitates carbon nanotubes (CNTs) formations with FeNx coordination in carbon matrix. The produced FeNx-CNTs catalyst shows excellent ORR activities with extremely high peak power density of 1.15 and 1.16 W cm−2 in anion and proton exchange membrane fuel cells, respectively.

Interpenetrating polymer network anion exchange membrane (IPN AEM) consists of cross-linked quaternized poly (vinylbenzyl chloride) and cross-linked poly (vinyl alcohol) is synthesized in this work. Electron microscope clearly reveals the IPN structure, and with this structural design, a highly efficient ion channel within IPN AEMs is constructed. This specially designed structure leads to high hydroxide (OH−) conductivity (e.g., 141.7 mS cm−1 at 80 °C) at a moderate ion exchange capacity (IEC) of 1.61 mmol g−1, and a remarkable peak power density of 0.64 W cm−2 with non-noble metal oxygen reduction reaction (ORR) catalyst in H2/Air (CO2-free) anion exchange membrane fuel cells (AEMFCs) test.

Fluid-shale interactions appear to significantly affect shale micromechanical properties, which regulate fracture network propagation during multistage hydraulic fracturing in shales and thus the gas production. While published works confirm that fluid-shale interactions can reduce Young's modulus and rock strength compared to dry shale samples, few attentions have been paid to unveil the nature of the physics with a combination of geochemical modelling and disjoining pressure isotherm, and fewer works have envisaged the effect of mineralogy (calcite-rich or quartz-rich rock) on shale weakening with presence of aqueous liquids. We hypothesize that fluid-mineral interactions likely generate electrical double layer force between mineral surfaces which would shift the disjoining pressure from strongly negative (mineral-air-mineral) to less negative or even positive (mineral-fluid-mineral) thus triggering Young's modulus reduction. To test the hypothesis, geochemical modellings including minerals dissolution (calcite, dolomite, quartz, pyrite and illite) and surface complexation were performed together with disjoining pressure isotherm using literature experimental data, accounting for the Young's modulus reduction induced by fluid-shale interactions. The geochemical modelling shows that the amount of mineral dissolution at in-situ condition is negligible, and thus may play a minor role in Young's modulus. Disjoining isotherm shows that both calcite and quartz (plane-plane geometry) give a strong negative disjoining pressure generated by van der Waals force and structural force in the presence of air, whereas the disjoining pressure can be shifted from strongly negative to less negative for calcite and even positive for quartz in presence of fluids due to the electrostatic force, suggesting a Young's modulus reduction due to the weaker adhesion in line with literature experimental data. This work provides an overall conceptual framework, which supports the hydraulic fracturing fluid design and treatment in shale reservoirs from geochemical and disjoining pressure isotherm perspectives.

CO2 huff-n-puff process appears to be important to unlock hydrocarbon resources from shale oil reservoirs after multi-stage hydraulic fracturing. While existing literature shows that CO2 diffusion plays a significant role in kinetics of oil recovery, few studies have been able to draw on any systematic research into fluid-shale interaction due to water uptake of CO2 in connate water (water carbonation), which governs fluids flow in fractures thus CO2 huff-n-puff performance. We therefore hypothesized that water carbonation would depress ion exchange process between oil and organic matter (OM) thus forming a more water-wet system. Moreover, water carbonation would also decrease the electrostatic forces between oil and edge charge on OM, thereby further promoting water-wet system. To test the hypothesis, we measured contact angles in non‑carbonated high salinity brine (HS), carbonated high salinity brine (CO2 HS) and carbonated low salinity brine (CO2 LS) at temperature of 25 °C and under pressure of 3000 psi. Moreover, a geochemical modelling was conducted to evaluate ion exchange and surface complexation reactions in three different brines. Our contact angle measurements showed that HS gave a contact angle of 130°, while CO2 HS and CO2 LS resulted a contact angle of 23.5° and 23.0°, suggesting a more water-wet system. Geochemical modelling shows that ion exchange reactions between oil and shale surfaces are dramatically depressed in carbonated brine. In particular, the bridges number between oil and shale surfaces decreases from 5.2 × 10−4 μmol/m2 to 5.3 × 10−6 μmol/m2 in carbonated brines, supporting the contact angle measurements. Moreover, the computed surface potential at oil and rock surfaces increases from around −40 mV to 150 mV, suggesting more repulsive forces in the presence of carbonated brine, further supporting contact angle results. This work reveals for the first time that water carbonation during CO2 huff-n-puff process likely triggers a hydrophilic shale surface, which may significantly affects multiphase flow in natural and hydraulic fractures in particular.

Subcritical crack growth in calcite-bearing reservoirs plays a vital role in rock deformation. Published experimental results show that fluid-rock interaction likely affects rock surface energy and triggers fracture propagation. However, much of research up to now has been only descriptive in nature, impairing a substantial interpretation to predict subcritical crack growth. In this study, we developed a physicochemical model to relate fluid-calcite interaction in particular surface potential to surface energy in light of capacitance theory. To test the model, we calculated calcite surface chemical species and surface potential as a function of pH, ion type and fluid salinity using surface complexation modeling. Moreover, we compared the predicted surface energy with Bergsaker et al.'s experimental measurements. Our results confirm that fluid chemistry would affect calcite surface species distribution and surface energy. At high acidic condition, lowering salinity increases surface potential of brine-calcite. At alkaline condition, lowering salinity decreases surface potential in the presence of MgSO4 and MgCl2 but increases that of Na2SO4. Furthermore, pH would affect the level of bonding-capable divalent such as Ca2+ through the equilibrium of calcite dissolution-precipitation, and thus indirectly influence surface energy. Our results unveil the importance of fluid-rock interaction on subcritical crack growth and shed light on hydrocarbon exploitation and CO2 capture and storage in carbonate reservoirs. These findings also delineate the inner connection between geochemical and geo-mechanical properties at subsurface.

Unlike conventional optics, plasmonics enables unrivaled concentration of optical energy well beyond the diffraction limit of light. However, a significant part of this energy is dissipated as heat. Plasmonic losses present a major hurdle in the development of plasmonic devices and circuits that can compete with other mature technologies. Until recently, they have largely kept the use of plasmonics to a few niche areas where loss is not a key factor, such as surface-enhanced Raman scattering and biochemical sensing. Here, we discuss the origin of plasmonic losses and various approaches to either minimize or mitigate them based on understanding of fundamental processes underlying surface plasmon modes excitation and decay. Along with the ongoing effort to find and synthesize better plasmonic materials, optical designs that modify the optical powerflow through plasmonic nanostructures can help in reducing both radiative damping and dissipative losses of surface plasmons. Another strategy relies on the development of hybrid photonic–plasmonic devices by coupling plasmonic nanostructures to resonant optical elements. Hybrid integration not only helps to reduce dissipative losses and radiative damping of surface plasmons, but also makes possible passive radiative cooling of nanodevices. Finally, we review emerging applications of thermoplasmonics that leverage Ohmic losses to achieve new enhanced functionalities. The most successful commercialized example of a loss-enabled novel application of plasmonics is heat-assisted magnetic recording. Other promising technological directions include thermal emission manipulation, cancer therapy, nanofabrication, nanomanipulation, plasmon-enabled material spectroscopy and thermo-catalysis, solar water treatment, and thermophotovoltaics., United States. Department of Energy. Office of Basic Energy Sciences (Grant DE-FG02-02ER45977), United States. Defense Advanced Research Projects Agency (Grant DE-AR0000471), Solid-State Solar-Thermal Energy Conversion Center (Award DE-SC0001299), Solid-State Solar-Thermal Energy Conversion Center (Award DE-FG02-09ER46577)

We demonstrate the agreement between first-principles calculations and experimental measurements of size effects in thermal transport in SiGe alloys without fitting parameters. Transient thermal grating (TTG) is used to measure the effect of the grating period on the temperature decay. The virtual crystal approximation under the density-functional-theory framework combined with impurity scattering is used to determine the phonon properties for the exact alloy composition of the measured samples. With these properties, classical size effects are calculated for the experimental geometry of reflection mode TTG using the recently developed variational solution to the phonon Boltzmann transport equation, which is verified against established Monte Carlo simulations. We find agreement between theoretical predictions and experimental measurements in the reduction of thermal conductivity (as much as fourfold of the bulk value) across grating periods spanning one order of magnitude. This paper provides a framework for the study of size effects in thermal transport in opaque materials.

Multi-stage hydraulic fracturing is an indispensable approach to enable shale oil available and affordable. However, a low flowback water recovery (usually Surface complexation modelling results show that the oil-brine-OM system wettability is primarily controlled by in-situ salinity and secondarily affected by pH and temperature. At a given pH, decreasing salinity triggers a greater positive surface potential for both oil and OM surfaces, implying a greater electrical double layer expansion thus hydrophilicity. Moreover, the surface potential for oil and OM decreases with increasing pH, which even would be shifted from positive to negative in the presence of low salinity water. Furthermore, the surface potential of both oil and OM decreases with increasing temperature at in-situ pH (from 3.5 to 7). The disjoining pressure results show that saturating sample from high salinity formation brine into the low salinity KCl solution will shift the disjoining pressure from negative values (attraction) to positive values (repulsion). Our results support the hypothesis that lowering salinity increases hydrophilicity of oil-brine-OM, which likely contributes to water uptake by shale. We also argue that geochemical modelling would be an effective tool to characterize the interaction of oil-brine-OM, providing insights into water uptake and enhanced oil recovery in shales.

Significance Thermoelectric technology can boost energy consumption efficiency by converting some of the waste heat into useful electricity. Heat-to-power conversion efficiency optimization is mainly achieved by decreasing the thermal conductivity in many materials. In comparison, there has been much less success in increasing the power factor. We report successful power factor enhancement by improving the carrier mobility. Our successful approach could suggest methods to improve the power factor in other materials. Using our approach, the highest power factor reaches ∼106 μW⋅cm −1 ⋅K −2 at room temperature. Such a high power factor further yields a record output power density in a single-leg device tested between 293 K and 868 K, thus demonstrating the importance of high power factor for power generation applications.

Tailoring the thermal conductivity of polymers is central to enlarge their applications in the thermal management of flexible integrated circuits. Progress has been made over the past decade by fabricating materials with various nanostructures, but a clear relationship between various functional groups and thermal properties of polymers remains to be established. Here, we numerically study the thermal conductivity of single-stranded carbon-chain polymers with multiple substituents of hydrogen atoms through atomic mass modification. We find that their thermal conductivity can be tuned by atomic mass modifications as revealed through molecular dynamics simulations. The simulation results suggest that heavy homogeneous substituents do not assist heat transport and trace amounts of heavy substituents can in fact hinder heat transport substantially. Our analysis indicates that carbon chain has the biggest contribution (over 80%) to the thermal conduction in single-stranded carbon-chain polymers. We further demonstrate that atomic mass modifications influence the phonon bands of bonding carbon atoms, and the discrepancies of phonon bands between carbon atoms are responsible for the remarkable drops in thermal conductivity and large thermal resistances in carbon chains. Our study provides fundamental insight into how to tailor the thermal conductivity of polymers through variable substituents., National Science Council (China) (51376069), National Key Basic Research Program of China (2013CB228302)