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The utilization of accelerators has been a common approach to prepare low‐temperature curable polyimide (PI). However, the accelerators have gradually fallen out of favor because of their excessive dosages and negative effect on the properties of PI. In this work, a new strategy of introducing accelerators by grafting to eliminate these disadvantages is presented. A novel quinoline derivative named 6‐([1,1′‐biphenyl]−4‐yl)−4‐chloroquinoline (NQL) is designed for this purpose, and an ultralow dosage of only 2.5 mol% is sufficient to prepare low‐temperature curable PI. The favorable low‐temperature curing effect of NQL is attributed to its strong alkalinity (pKa = 18.47) and electron‐donating ability. At a curing temperature of 200 °C, the PI with 2.5 mol% NQL showed outstanding properties (Young's modulus of 5.73 GPa, elongation of 37.3%, tensile strength of 237 MPa, and coefficient of thermal expansion of 16 ppm K−1). In particular, NQL can even lower the curing temperature to 180 °C and the ultralow temperature curable PI film still retains excellent properties. These results demonstrate that introducing low‐temperature curable accelerators by partial grafting instead of blending is a promising way to furnish low‐temperature curable PI, and provide insights into the preparation of polyimide with high performance in advanced packaging. [ABSTRACT FROM AUTHOR]

There is an increasing demand for polyimide (PI) with excellent mechanical properties, good heat resistance, and low dielectric constant in integrated circuits and advanced packaging. Based on this, we report a strategy of tailoring the PI via fluorinated nanofillers modification to improve its mechanical properties, heat resistance, hydrophobicity, and reduce its dielectric constant. Specifically, different fluorinated nanofiller, including fluorinated graphene (FG), fluorinated carbon nanotubes (FCNT), fluorinated carbon black (FCB), and fluorinated graphene quantum dots (FGQD) were introduced into PI matrix to prepared composite films by a simple method of in‐situ polymerization, and the effect of different nanofillers on the properties of polyimide was systematically investigated. The results showed that the introduction of fluorinated nanofillers significantly improved the comprehensive performance of the composite films, especially the FGQD. FGQD/PI composite film with 0.5 wt% FGQD exhibits superior tensile strength (145.8 MPa), Young's modulus (2.83 GPa) and elongation at break (45.4%) the best comprehensive performance which are 10.0%, 19.4%, and 32.0% of those of pure PI, respectively. Most importantly, the FGQD/PI composite film shows decreased dielectric constant (from 3.38 to 2.93) at 1 MHz improved hydrophobicity and excellent heat resistance. The FGQD/PI composite film exhibits excellent comprehensive performance, thereby showing the potential in the future development of advanced packaging and microelectronics industry. [ABSTRACT FROM AUTHOR]

One challenge in the high‐performance dielectric material of polyimide (PI) is to obtain the excellent comprehensive properties at low curing temperature for advanced IC package. In this work, 6‐aminoquinoline (AQL) is introduced through covalent bonds for end capping to obtain a low‐temperature curable PI at first. The results demonstrate that with very limited introduce (2.76%) of AQL, the imidization index could reach as high as 1.01 at 200°C. Then, fluorinated nano carbon (FC) is further introduced resulting in the fluorinated nano carbon/polyimide (FCPI) composites, which effectively reduces the dielectric constant (1 wt%, 2.75 @ 1 MHz). Besides, the as‐prepared FCPIs also possess excellent thermal property of which FCPI‐0.3 exhibited the 5% weight loss temperature of 540°C and the glass transition temperature is also as high as 385°C. Furthermore, the tensile strength of the film is 127 MPa, the elongation at break is around 15.82%, and the Youngs' modulus is about 3.10 GPa proving the superior mechanical property. As a result, the successful preparation of the FCPI nanocomposites not only possess low‐temperature curing and low‐dielectric performance but also exhibit excellent thermal and mechanical properties, which shows a wide range of application prospects in the field of microelectronics for the advanced electronic package. [ABSTRACT FROM AUTHOR]

The mechanical properties of shales, a type of heterogeneous and multiphase composite, are of multiscale characteristics in nature. A large number of indentation measurements were performed under the continuous stiffness measurement (CSM) mode on the Longmaxi shale, followed by data segmentation, Gaussian mixture modeling (GMM) deconvolution of segmented datasets, and results re-integration. Accompanying compositional analyses by X-ray powder diffraction and surface imaging were also conducted to assist data interpretation. Results showed that the studied shale consisted of a fine-grained, relatively homogeneous clay matrix with randomly embedded, coarse-grained solid inclusions of up to ~ 100 μm in size. The CSM mode enabled the analysis of phase angle lag, which is an effective indicator for surface roughness. The Young's moduli of both microscopic constituent phases (e.g., clay matrix, carbonates, quartz, pyrite) and macroscopic bulk shale were precisely determined and, through the probability analysis of the indent locations, the characteristic lengths of the shale's constituent phases were estimated. The clay matrix and carbonates have relatively large characteristic lengths than quartz and pyrite. The data analytics proposed in this study may provide a feasible framework to assess the multiscale mechanical properties as well as the characteristic lengths of the shale's constituent phases via a single type of measurement technique on the same piece of sample. [ABSTRACT FROM AUTHOR]

This paper presents a newly observed phenomenon of upscaling of rocks' properties using big data nanoindentation and analytics involving Gaussian mixture modeling (GMM), leading to characterizing the cross-scale mechanical properties of four shales and one sandstone. A large number (i.e., ~ 500) of statistical indentation measurements to depths of 6–8 μm were performed on each rock, resulting in continuous depth-dependent hardness and Young's modulus data from unknown phases, which were then segmented at various depths to extract an array of discretized subdatasets. Two-dimensional GMM of each subdataset yields the number, fraction, and properties of mechanically distinct phases, and re-assembly of these results leads to clearly discernible property-depth curves. Such improved data analytics consisting of data segmentation, GMM deconvolution, and re-assembly enables the transformation of a massive number of chaotic curves from unknown phases into a few discernible lines corresponding to identified phases, from which the mechanical properties of individual phases are accurately determined at relatively small depths. With increasing depth, initially unique mechanical properties of individual phases undergo multistage merging at the intermediate mesoscale and progressively homogenize into a unified value at large depths or macroscale (e.g., > ~ 5 μm), which is regarded as the bulk rock's properties. More importantly, such depth-dependent transition and progressive merging and homogenization actually manifest the micromechanics of nanoindentation on a heterogeneous composite, including the indentation surround effect and rock's microstructure (e.g., sizes and spacings of different solid particles and their properties). Compared to different micromechanical upscaling models, this newly developed big data indentation technique and pertinent data analytics enable more accurate, multi-parameter, and cross-scale characterization of highly heterogeneous materials and explicitly uncover the multi-staged, progressively-homogenized, depth-dependent upscaling of elasticity from individual constituents at the nanoscale to merged virtual interface phases at the mesoscale and to bulk material at the macroscale. [ABSTRACT FROM AUTHOR]

A novel statistical nanoindentation technique is presented that obtains massive data on the basis of shale sample's large volume (LV) to assess water-induced softening in terms of Young's moduli of both individual minerals at the micro/nano-scale and the bulk rock at the macroscale, with the latter extracted by a newly proposed surround effect model. Distinguished from traditional statistical nanoindentation that only examines the material at shallow depths of up to a few micrometers, this LV-based method obtains successive measurements to much larger depths of up to ~ 300 μm via sacrificial removal of the previously indented surface layer, enabling assessment of changes in mechanical properties over a large volume. Natural shale sample was first hydrothermally treated to cause softening, followed by statistical indentation with continuous stiffness measurement (CSM) on successive layers of increasing depth upon removal by polishing of the prior tested layers. For each tested surface, cumulative distribution function (CDF)-based deconvolution was performed to analyze multiple subsets of the massive data (i.e., ~ 1000 curves), each of which was extracted from the CSM curves via segmentation at a fixed depth. Such results on different segmentation depths were then fitted by the surround effect model to extract the Young's modulus of individual minerals and bulk rock. The clay matrix is highly sensitive to rock–water interactions and its Young's modulus decreases significantly from 29.2 to 16.5 GPa upon 30 days' treatment. The average rate of softening advancement was estimated to be ~ 10.5 μm/day, suggesting that softening advancement is intrinsically controlled by permeability, despite various physical and chemical softening mechanisms. [ABSTRACT FROM AUTHOR]

Light-activated self-healing (LSH) materials have received extensive attentions recently due to their environmentally friendly repairing methods and excellent healing performance. However, the current reported LSH materials have poor mechanical strength and elasticity, which limit their applications. Herein, a novel series of coumarin-based polyurethanes with enhanced mechanical properties and elasticity have been synthesized which possessed a dramatic breaking stress of 27 MPa with a high breaking strain of 890%. Besides, the energy dissipation efficiency in continuous stretch cycles of the as-prepared polyurethanes varied negligibly, which proves the as-prepared LSHs have excellent elasticity. Meanwhile, after cutoff, the polymers exhibited excellent self-healing performance by UV irradiation for 40 min and the best healing efficiency of strain, stress and Young's modulus were 84%, 92%, 94%, respectively. The prepared self-healing polyurethanes showed great potential applications in the fields of smart materials such as self-healing coatings, electrochemical sensors and devices, electronic skin, etc. Image 1 • The first study to synthesize the light-activated self-healing polyurethanes based on coumarin with excellent elasticity. • The mechanical properties of this polymers are better than other coumarin polymers. • The polymers exhibited superior self-recovery performance. [ABSTRACT FROM AUTHOR]

This paper presents an integrated experimental and computational study of the compression behavior of individual thin-walled metallic hollow spheres (MHS) with patterned distributions of microporosity. Quasi-static compression testing, including purely elastic loading, was conducted on two groups of individual MHS with two different sizes to examine the entire deformation process as well as the purely elastic response. Three-dimensional finite element modeling was then performed to investigate the effects of different microporosity distribution patterns on the MHS compression behavior and to understand the pertinent deformation and failure mechanisms. Results show that the Young's modulus and collapse stress of individual MHS with a uniform microporosity distribution decrease nonlinearly with porosity, which follows the same power-law functions developed for the porous wall material. For other patterned (i.e., vertical, horizontal, and random) distributions of microporosity involving localized weak wall sections, buckling commences at the weak sections, generating “buckling lines”, followed by buckling failure along these adjacent or converged “buckling lines”. Moreover, among the “buckling lines” generate some hinges that contribute to the increased load-bearing capability during the densification process. These findings can shed lights on the design, manufacturing, and modeling of individual MHS and MHS-based materials with specifically tailored engineering performance. [ABSTRACT FROM AUTHOR]

The production of coarse-grained aggregates and sands from tuff, a naturally occurring rock composed of primarily fine volcanic detritus, usually generates 20 wt% powder as a solid waste. This paper presents the attempt to synthesize two high-performance, low carbon footprint, binders using fine tuff powder: a tuff-based binder (TBB) and a tuff and ground granulated blast-furnace slag (GGBS)-based binder (T-GGBS). The maximum compressive strength, flexural strength, Young's modulus, and density of the NaOH and Na-silicate activated TBB cured at 60 °C for 28 days are 71.3, 17.0, 2100 MPa, and 1892 kg/m3 respectively, while those for the T-GGBS are 73.3, 15.8, and 1980 MPa, and 1880 kg/m3. To reveal the mechanisms for their high performance, an array of microstructure characterizations were performed on both the raw materials and final binders. For the TBB, the surfaces of irregular angular crystalline constituents in the tuff powder are partially dissolved and activated, while the undissolved part plays a key role as skeletons, as evidenced by the decrease of crystalline phases but increase in the N-A-S-H with increasing the NaOH concentration. For the T-GGBS, the amorphous GGBS constituents are fully dissolved and hence change the main product from the N-A-S-H gel to N/C-A-S-H cross-linked gel etc. However, overdosage of the GGBS consumes the majority of NaOH but leaves little to the reaction of tuff particles, most of which hence just act as inert fillers rather than reactants in the final binders. The effects of porosity on the mechanical performance are also discussed with reference to conventional geopolymers. • Two alkali-activated tuff-based binders were synthesized with low carbon footprint. • Their optimum strengths without and with 20 wt% GGBS reach 71.3 and 73.3 MPa. • The tuff-based binders consist of partially reacted crystalline constituents. • The added GGBS consumes most NaOH and leaves the tuff particles as inert fillers. • NASH and C/NASH are the main cementitious products in the binders. [ABSTRACT FROM AUTHOR]

• Nanoindentation (Ni) was used to characterize cement-elastomer composites. • Big data Ni (BDNi) can characterize cross-scale mechanical properties. • Emulsion and particulate elastomers play different roles in microstructure. • Hematite can counteract the influence of elastomers. • Multiple functioning phases contribute to the overall behavior of composites. Intensive big data nanoindentation (BDNi) characterization was performed to reveal the cross-scale mechanical properties of, and hence distinguish the different phases in, inorganic–organic hybrid oilwell cement-elastomer composites, hydrothermally cured at 160 °C and 20 MPa for 28 days. Totally-three emulsified and particulate elastomers, including styrene-butadiene latex (SBL) emulsion (6, 12, and 14 wt.%), polypropylene (PP) powder (12 wt.%), and nitrile rubber (NR) powder (6 wt.%), and a weighting agent, hematite (50 wt.%), were used as additives to finely adjust the mechanical properties and microstructure of the hybrid composites, which were respectively examined by the BDNi and mercury intrusion porosimetry and scanning electron microscopy. BDNi data were statistically deconvoluted by the Gaussian mixture modeling (GMM) to discern mechanically distinct phases and their Young's moduli and hardness at the micro/nano scale and the bulk composites' properties at the macro scale. Results show that the SBL emulsion can be more homogeneously dispersed into the cement matrix, due to its emulsified soft consistency and hydrophilicity, resulting in the formation of soft coatings on, and softer infills intermixed with, the cement hydration products (CHPs). In contrast, the two hydrophobic, inert, particulate elastomers, PP and NR powders, only act as isolated soft inclusions embedded in the hydrated cement matrix. The NR melts at high temperatures and permeates into the pores of the cement matrix, leading to the formation of complex intervened micromorphology and hence functions better than the PP. All elastomers can effectively reduce the composites' Young's moduli: with increasing the elastomer contents, while the modulus of a BDNi-identified major CHP phase decreases from 20.9 to 11.3 GPa, the bulk composites' counterpart from 17.3 to 10.7 GPa. The BDNi enables the identification of multiple mechanically distinct phases in the hybrid composites and quantification of the property changes of these phases. [ABSTRACT FROM AUTHOR]

The creep of shales affects the fracture conductivity, well production rate, and hence ultimate recovery of hydrocarbons from reservoir formations. This paper presents an experimental study of the creep characteristics of a shale softened by thermo-hydro-mechano-chemical (THMC) treatments that mimic the rock-fluid interactions affected by high temperature, high pressure, and hydraulic fracturing fluids. Microindentation was conducted to characterize the creep behavior of the THMC-treated specimens with the data analyzed by the Kelvin-Voigt (KV) and compliance methods, while X-ray diffraction and scanning electron microscopy were performed to analyze the compositional and microstructural changes respectively to aid interpretation of indentation measurements. Results show that the THMC treatments increase the creep rate by 46–162%, owing to the treatment-induced softening that varies with the treatment time and distance from the fluid-rock interface, while the Young's modulus and hardness decrease with both the THMC-treatment and creep durations. The softened zones become more viscous, as reflected by the decreased KV model's viscoelastic coefficients for the softened specimens. The higher creep rate of the softened zones is primarily attributed to the weakening in cementation bond and increase in microscale porosity due to the dissolution of carbonates. The findings help understand the mechanisms for creep deformation and pertinent proppant embedment in fractured shales, and hence can be used to predict shale gas production and optimize fracturing fluid additives and stimulants. [ABSTRACT FROM AUTHOR]

Low-temperature curable and low-dielectric polyimides (PIs) are required in wafer-level packaging (WLP) which is an advanced microelectronic packaging technology. Herein, a low-cost and multifunctional nanofiller (aminoquinoline-functionalized graphene oxide, AQL-GO) is synthesized, which ingeniously achieved the above-mentioned requirements of polyimide nanocomposites by nucleophilic attack of QL and chaotic packing of the polymer chain. The results show that the nanocomposite can be fully cured at only 200 °C and have a low dielectric constant (2.96@1 MHz) with 0.5 wt% addition of AQL-GO. Furthermore, the mechanical and thermal properties of all nanocomposites cured at 200 °C (the elongation at break can reach 39.69%, the Young's modulus can reach 2.38 GPa and T 5% can reach 530.55 °C) are almost equal or even better than those of pure PI cured at 350 °C. Therefore, the PI/AQL-GO nanocomposites have industrial prospects in advanced microelectronic packaging. Low-temperature curing (200 °C) and low-dielectric (2.96@1 MHz) polyimide/aminoquinoline-functionalized graphene oxide (PI/AQL-GO) nanocomposites have been synthesized for next-generation microelectronic packaging. [Display omitted] • Polyimide/aminoquinoline-functionalized graphene oxide (PI/AQL-GO) nanocomposites were successfully synthesized. • The nanocomposites can be fully cured at 200 °C and possess low dielectric constant (2.96@1 MHz). • The nanocomposites also possess excellent mechanical and thermal properties. • In situ grafting process was proposed to explain the mechanism. [ABSTRACT FROM AUTHOR]

One challenge in tailoring polyimide (PI) for microelectronics is to obtain excellent properties of films when cured at low temperature. To meet this challenge, this study put forwards an investigation of pyrazine moieties incorporated polyimide, which is comprehensively investigated on curing temperature dependence with thermal, mechanical, and dielectric properties. Self-catalytic effect stemming from pyrazine moiety has a significant improvement on imidization degree of PI films from 10.1% to 13.3% under 200 °C as revealed with ATR-FTIR spectrum. The resulting low temperature cured polyimide films with higher imidization degree exhibit excellent comprehensively properties. It is demonstrated that PI-1 shows high tensile strength (136 MPa), high Young's modulus (3.4 GPa) and low CTE value (4.7 ppm/°C) when cured at 200 °C. Besides, the temperature for 5% weight loss as high as 556 °C and glass transition temperature (T g) as 367 °C of the PI film turn out to be superior thermal stability. Moreover, molecular dynamics simulation was carried out to get a theoretical perspective on the effect of intrinsic factors on a microscopic level associated with the molecular structure of the polyimides to gain a deeper view on the effect of imidizaiton degree on the T g , chain mobility and conformational rigidity. This research gives a comprehensive study of pyrazine constructed polyimide for low-temperature cured polyimide and paves a way for its application in the microelectronics. Low temperature curable polyimides are synthesized and studied with 4,4'-(pyrazine-2,5-diyl)dianiline monomer showing excellent comprehensive properties, and the effect of imidizaiton degree on the T g , chain mobility and conformational was investigated by molecular dynamics simulation. [Display omitted] • 4,4'-(pyrazine-2,5-diyl)dianiline is synthesized to prepare low temperature curable polyimide. • Catalytic effect of pyrazine moiety in monomer can improve imidization degree of PI films from 10.1% to 13.3% under 200 °C. • Molecular dynamics simulation was carried out to understand relationship between imidizaiton degree and T g. [ABSTRACT FROM AUTHOR]

Cross-scale mechanical characterization of two sandstones was performed using big data statistical nanoindentation involving continuous stiffness measurement to profile the depth-dependent changes in Young's modulus and hardness, with a particular focus on the evaluation of three different data analytics and four upscaling models. A massive number (i.e., >1000) of indents with depths of up to ~6000 nm were made on each of the two sandstones with highly contrasting microstructures and dissimilar compositions, followed by intensive data processing using the recently developed data analytics consisting of data segmentation to extract subdatasets at various depths, statistical deconvolution of each subdataset to identify mechanically distinct phases, re-assembly of results from different subdatasets, and indentation surround effect modeling to extract the properties of both individual phases and bulk rocks. Moreover, the composition and microstructure of the two sandstones were analyzed by quantitative X-ray diffraction and electron microscopy with elemental mapping, respectively. The new development is the three different statistical deconvolution techniques, including probability density function (PDF), cumulative distribution function (CDF), and Gaussian mixture modeling (GMM), used for data processing. Moreover, four micromechanical homogenization and upscaling models were also employed to derive Young's moduli of the two bulk rocks using experimental results. Surprisingly, the three deconvolution techniques yield similar results, and GMM can provide more accurate phase separation due to the use of two-dimensional datasets. Yet, none of the four upscaling models works well for the two rocks. These results manifest well the rocks' mineralogical composition and microstructure: while one consists of primary, inter-contacted, coarse-grained skeleton with secondary fine-grained particles filling the pores, the other is mainly made of primary fine-grained clay matrix with a large fraction of coarse particles as isolated inclusions. [ABSTRACT FROM AUTHOR]

This paper describes a viable nanoindentation-enhanced technique for screening hydraulic fracturing fluid additives via quantifying the effects of rock-fluid interactions on the mechanical properties of a clay-rich shale. Big data nanoindentation testing was conducted on both the intact shale and counterparts hydrothermally treated by four fracturing fluids, including water, KCl solution, and two surfactants, to extract simultaneously the statistical, cross-scale mechanical properties of both the bulk rock and individual constituent phases (e.g., clay matrix, carbonate, and quartz), accompanied by scanning electron microscopy for surface imaging and elemental mapping. Results show that pure water and KCl solution significantly degrade the clay matrix's Young's modulus and hardness by up to 39.4–42.5% and 42.9–57.1%, respectively, which can be mitigated or prevented by appropriate surfactant additives. The physicochemical rock-fluid interactions, such as dissolution of carbonate, are mainly responsible for the property degradation, as evidenced by the hydrothermal treatment-induced large cavities and secondary pores on the surface that tend to impair microstructural integrity of the shale. The big data nanoindentation technique can be implemented as an adaptive toolkit for screening, tailoring, and optimizing the chemical additives in fracturing fluids used for a specific shale formation to prevent shale softening, protect reservoir stability, and maximize well production. [ABSTRACT FROM AUTHOR]

An experimental study is presented of the elastic anisotropy of a shale at different length scales probed by a cross-scale, big data-based, statistical nanoindentation technique. A large number (~1000) of indentation measurements with depths of up to ~8 μm were conducted under continuous stiffness measurement mode on each of three differently oriented (i.e., 0°, 45°, and 90° relative to the bedding plane) samples, yielding massive depth-dependent Young's modulus datasets for different orientations. Segmentation at different depths of these continuous modulus-depth curves resulted in multiple sub-datasets that were statistically deconvoluted, leading to the extraction of Young's moduli of mechanically distinct phases at each segmentation depth, which were then re-assembled against depth. Such modulus-depth curves, each pertaining to a specific phase, were further fitted by the surround effect model to determine the elastic moduli of individual minerals at the microscale and the bulk rock at the macroscale. Results show that the shale possesses multiscale elastic anisotropy: at the macroscale, the bulk rock's horizontal Young's modulus is 1.24 times greater than the vertical counterpart; at the microscale, the clay matrix is highly anisotropic, with anisotropy ratios of 1.36 and 1.96 at the 45° and 90° orientations referenced to the bedding plane, while the anhedral, coarse-grained minerals (i.e., quartz and feldspar) are only slightly anisotropic owing to their random orientation and equidimensional geometry, suggesting that the macroscale elastic anisotropy is mainly attributed to the highly anisotropic clay matrix that acts as a major load-bearing medium, but disturbed by isolated, randomly distributed silt and sand particles embedded as solid inclusions in the clay matrix. As such, the degree of anisotropy decreases with increasing length scale. The origin, formation, and evolution of such multiscale anisotropy are discussed in terms of the shale's composition, depositional history, and post-depositional geological processes. Image 1 • Multiscale anisotropy of a shale was probed by cross-scale nanoindentation. • Macroscale anisotropy of bulk rock stems from highly anisotropic clay matrix. • Anisotropic but randomly oriented silt/sand inclusions reduce the anisotropy. • The degree of anisotropy of shale decreases with increasing length scale. • Anisotropy of shales evolves through post-depositional geologic processes. [ABSTRACT FROM AUTHOR]