Characteristics of evolution of mining-induced stress field in the longwall panel:insights from physical modeling

The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stress field.This study investigated its evolution by constructing a large-scale physical model according to the in situ conditions of the longwall panel.Theoretical analysis was used to reveal the mechanism of stress distribution in the overburden.The modelling results showed that:(1)The major principal stress field is arch-shaped,and the strata overlying both the solid zones and gob constitute a series of coordinated load-bearing structures.The stress increasing zone is like a macro stress arch.High stress is especially concentrated on both shoulders of the arch-shaped structure.The stress concentration of the solid zone in front of the gob is higher than the rear solid zone.(2)The characteristics of the vertical stress field in different regions are significantly different.Stress decreases in the zone above the gob and increases in solid zones on both sides of it.The mechanical analysis show that for a given stratum,the trajectories of principal stress are arch-shaped or inverselyarched,referred to as the‘‘principal stress arch’’,irrespective of its initial breaking or periodic breaking,and determines the fracture morphology.That is,the trajectories of tensile principal stress are inversely arched before the first breaking of the strata,and cause the breaking lines to resemble an inverted funnel.In case of periodic breaking,the breaking line forms an obtuse angle with the advancing direction of the panel.Good agreement was obtained between the results of physical modeling and the theoretical analysis.

Stretchable supercapacitor based on a hierarchical PPy/CNT electrode and hybrid hydrogel electrolyte with a wide operating temperature

Hydrogel is frequently used as a solid electrolyte for all solid-state supercapacitors(SCs)because of its liquid-like ion-transport property and high conformability.However,due to the higher water content,the hydrogel electrolyte undergoes inevitable freezing and/or dehydration with climate change.Herein,polypyrrole/carbon all-solid-state SCs(PCSCs)were developed based on a hierarchical polypyrrole/carbon nanotube electrode and a highly stretchable double-network polymer hydrogel electrolyte with LiCl/ethylene glycol as a mixed solvent.The PCSCs showed excellent electrochemical performance and cycle stability with a wide operating temperature.The specific capacitances could reach 202.2 and 112.3 mF cm^(−2) at current densities of 0.5 and 3.0 mA cm^(−2),respectively.Meanwhile,the PCSCs showed outstanding mechanical properties in maintaining a high areal capacitance under deformations of bending and tension.The excellent water retention of the device also ensured the stable electrochemical performance of PCSCs in a wide temperature range(30–80℃),which could potentially represent a reliable application in various harsh environments.

Highly Stretchable,Elastic,and Sensitive MXene-Based Hydrogel for Flexible Strain and Pressure Sensors

Electronic skin is driving the next generation of cutting-edge wearable electronic products due to its good wearability and high accuracy of information acquisition.However,it remains a challenge to fulfill the requirements on detecting full-range human activities with existing flexible strain sensors.Herein,highly stretchable,sensitive,and multifunctional flexible strain sensors based on MXene-(Ti_(3)C_(2)T_(x)-)composited poly(vinyl alcohol)/polyvinyl pyrrolidone double-network hydrogels were prepared.The uniformly distributed hydrophilic MXene nanosheets formed a three-dimensional conductive network throughout the hydrogel,endowing the flexible sensor with high sensitivity.The strong interaction between the double-network hydrogel matrix and MXene greatly improved the mechanical properties of the hydrogels.The resulting nanocomposited hydrogels featured great tensile performance(2400%),toughness,and resilience.Particularly,the as-prepared flexible pressure sensor revealed ultrahigh sensitivity(10.75 kPa^(-1))with a wide response range(0-61.5 kPa),fast response(33.5 ms),and low limit of detection(0.87 Pa).Moreover,the hydrogel-based flexible sensors,with high sensitivity and durability,could be employed to monitor fullrange human motions and assembled into some aligned devices for subtle pressure detection,providing enormous potential in facial expression and phonation recognition,handwriting verification,healthy diagnosis,and wearable electronics.

Ultradurable,freeze-resistant,and healable MXene-based ionic gels for multi-functional electronic skin

Hydrogel is a potential matrix material of electronic-skins(E-skins)because of its excellent ductility,tunability,and biocompatibility.However,hydrogel-based E-Skins will inevitably lose their sensing performance in practical applications for water loss,physical damage,and ambient interferences.It remains a challenge to manufacture highly durable gel-based E-skins.Herein,an E-Skin is fabricated by introducing ionic liquids(ILs)into MXene-composited binary polymer network.The obtained ionic gel shows excellent mechanical properties,strong adhesion,and superior tolerance to harsh environments.The E-skin exhibits high sensitivity to both strain and pressure in a wide range of deformations,which enables a monitoring function for various human motions and physiological activities.Importantly,the E-skin shows consistent electrical response after being stored in the open air for 30 days and can be quickly healed by irradiation with 808 nm near-infrared light,originating from the photo-thermal effect induced self-healing acceleration.It is noteworthy that the E-skin also reveals a highly sensitive perception of temperature and near-infrared light,displaying the promising potential applications in the multifunctional flexible sensor.

Thermoresponsive Lignin-Reinforced Poly(Ionic Liquid)Hydrogel Wireless Strain Sensor

To meet critical requirements on flexible electronic devices,multifunctionalized flexible sensors with excellent electromechanical performance and temperature perception are required.Herein,lignin-reinforced thermoresponsive poly(ionic liquid)hydrogel is prepared through an ultrasound-assisted synthesized method.Benefitting from the electrostatic interaction between lignin and ionic liquid,the hydrogel displays high stretchability(over 1425%),excellent toughness(over 132 kPa),and impressive stress loading-unloading cyclic stability.The hydrogel strain sensor presents excellent electromechanical performance with a high gauge factor(1.37)and rapid response rate(198 ms),which lays the foundation for human body movement detection and smart input.Moreover,owing to the thermal-sensitive feature of poly(ionic liquid),the as-prepared hydrogel displays remarkable thermal response sensitivity(0.217℃^(-1))in body temperature range and low limit of detection,which can be applied as a body shell temperature indicator.Particularly,the hydrogel can detect dual stimuli of strain and temperature and identify each signal individually,showing the specific application in human-machine interaction and artificial intelligence.By integrating the hydrogel strain sensor into a wireless sensation system,remote motion capture and gesture identification is realized in real-time.

MXene-composited highly stretchable,sensitive and durable hydrogel for flexible strain sensors

The flourishing development in flexible electronics has provoked intensive research in flexible strain sensors to realize accurate perception acquisition under different external stimuli.However,building hydrogel-based strain sensors with high stretchability and sensitivity remains a great challenge.Herein,MXene nanosheets were composited into polyacrylamide-sodium alginate matrix to construct mechanical robust and sensitive double networked hydrogel strain sensor.The hydrophilic MXene nanosheets formed strong interactions with the polymer matrix and endowed the hydrogel with excellent tensile properties(3150%),compliant mechanical strength(2.03 kPa^(-1)in Young’s Module)and long-lasting stability and fatigue resistance(1000 dynamic cycles under 1,600%strain).Due to the highly oriented MXene-based three dimensional conductive networks,the hydrogel sensor achieved extremely high tensile sensitivity(18.15 in gauge factor)and compression sensitivity(0.38 kPa^(-1)below 3 kPa).MXene hydrogel-based strain sensors also displayed negligible hysteresis in electromechanical performance,typical frequent-independent feature and rapid response time to external stimuli.Moreover,the sensor exhibited accurate response to different scales of human movements,providing potential application in speech recognition,expression recognition and handwriting verification.

原位沉积多层集成水凝胶用于可变形拉伸超级电容器

因其固有的机械弹性和离子电导率,水凝胶体系极大地促进了柔性储能设备的发展.然而,对于水凝胶装置而言,在剧烈的机械变形下实现稳定的能量存储仍然是一个挑战.本文通过在离子结合水凝胶电解质的两侧原位沉积聚苯胺/氧化石墨烯(PANI/GO)纳米复合材料,组装一体化集成超级电容器(AISC),简化了器件组装过程,并避免了水凝胶储能器件在机械变形过程中多层结构的置换和分离;同时,离子添加剂水凝胶电解质表现出较强的粘附性、柔韧性以及高离子电导率,确保了AISC优异的比电容和倍率性能.其在0.2 mA cm^(−2)电流密度下比电容为222.8 mF cm^(−2),在3.2 mA cm^(−2)电流密度下比电容为151.7 mF cm^(−2),电容保持率为68.1%.器件在120.0μW cm^(−2)的功率密度下,能量密度达到44.6μW h cm^(−2).此外,在弯曲、压缩和拉伸的变形下可以获得稳定的能量存储,串联组装的AISC可以为LED灯供电.该工作在改善超级电容器机械性能的同时进一步提高了其电学性能,为构建新型柔性超级电容器提供了一种新策略.

Thermoresponsive Lignin-Reinforced Poly(Ionic Liquid) Hydrogel Wireless Strain Sensor

To meet critical requirements on flexible electronic devices,multifunctionalized flexible sensors with excellent electromechanical performance and temperature perception are required.Herein,lignin-reinforced thermoresponsive poly(ionic liquid)hydrogel is prepared through an ultrasound-assisted synthesized method.Benefitting from the electrostatic interaction between lignin and ionic liquid,the hydrogel displays high stretchability(over 1425%),excellent toughness(over 132 kPa),and impressive stress loading-unloading cyclic stability.The hydrogel strain sensor presents excellent electromechanical performance with a high gauge factor(1.37)and rapid response rate(198 ms),which lays the foundation for human body movement detection and smart input.Moreover,owing to the thermal-sensitive feature of poly(ionic liquid),the as-prepared hydrogel displays remarkable thermal response sensitivity(0.217℃^(-1))in body temperature range and low limit of detection,which can be applied as a body shell temperature indicator.Particularly,the hydrogel can detect dual stimuli of strain and temperature and identify each signal individually,showing the specific application in human-machine interaction and artificial intelligence.By integrating the hydrogel strain sensor into a wireless sensation system,remote motion capture and gesture identification is realized in real-time.