A facile and efficient method was developed to prepare highly stretchable and conductive graphene conductors with wrinkled structures by the mechanical stretching and shrinking of elastomeric substrates, in which graphene inks were printed on a prestretched elastomeric substrate. Stretchable and exfoliated graphene inks were prepared by mixing graphite and Ecoflex in a shear-assisted fluid dynamics reactor. The resultant graphene conductor exhibited excellent stretchability at 150% strain and high electrical conductivity of 64 ± 1.2 S m− 1. The resistance of the conductor did not change in bent, twisted, and stretched states. The resistance did not change during 10,000 cycles of stretching/releasing, with a maximum strain of 150%. Based on the graphene conductor, a stretchable conductometric sensor with a two-electrode configuration was fabricated to measure impedance changes at different concentrations of electrolyte ions. This sensor exhibited a good and linear sensitivity curve (298.61 Ω mM− 1, R2 = 0.999) in bent and stretched states.

Flexible zinc-air batteries have many merits, including low cost, high safety, environmentally friendliness applicability, etc. One of the key factors to improve the performance of flexible zinc-air batteries is to use a gel electrolyte. In this study, gel electrolytes were synthesized from potato, sweet potato, and corn starch. In a comparison of each starch, the corn starch-based gel electrolyte showed the highest discharge capacity of 12.41 mAh/cm2 in 20 mA and 6.47 mAh/cm2 in 30 mA. It also delivered a higher specific discharge capacity of 7.06 mAh/cm2 than the other materials after 100° bending. In addition, the electrochemical impedance spectroscopy (EIS) was analyzed to calculate the ionic conductivity. The potato, sweet potato, and corn starch-based gel electrolytes showed electrolyte resistances (Re) of 0.306, 0.298, and 0.207 Ω, respectively. In addition, the corn starch-based gel electrolyte delivered the highest ionic conductivity of 0.121 S cm-1 among the other gel electrolytes. Thus, the corn starch-based gel electrolyte was verified to improve the performance of flexible zinc-air batteries

Piezoelectric composite films which are enabled by inorganic piezoelectric nanomaterials-embedded polymer, have attracted enormous attention as a sustainable power source for low powered electronics, because of their ease of fabrication and flexible nature. However, the absorption of applied stress by the soft polymeric matrices is a major issue that must be solved to expand the fields of piezoelectric composite applications. Herein, a flexible and porous piezoelectric composite (piezoelectric sponge) comprised of BaTiO3 nanoparticles and polydimethylsiloxane was developed using template method to enhance the energy conversion efficiency by minimizing the stress that vanishes into the polymer matrix. In the porous structure, effective stress transfer can occur between the piezoelectric active materials in compression mode due to direct contact between the ceramic particles embedded in the pore-polymer interface. The piezoelectric sponge with 30 wt% of BaTiO3 particles generated an open-circuit voltage of ~12 V and a short-circuit current of ~150 nA. A finite element method-based simulation was conducted to theoretically back up that the piezoelectric output performance was effectively improved by introducing the sponge structure. Furthermore, to demonstrate the feasibility of pressure detecting applications using the BaTiO3 particles-embedded piezoelectric sponge, the composite was arranged in a 3 × 3 array and integrated into a single pressure sensor. The fabricated sensor array successfully detected the shape of the applied pressure. This work can provide a cost-effective, biocompatible, and structural strategy for realizing piezoelectric composite-based energy harvesters and self-powered sensors with improved energy conversion efficiency

Due to its capacity to manufacture low-cost 3D-printed structures, 3D-printing technology offers a unique opportunity for the fast epitome of various applications. Using a typical fused deposition modeling 3D printer along with a Discovery extruder, a graphene-ink can be 3D printed to produce an interdigitated electrode (IDE) arrangement. This work fabricated a 3D-printed planar supercapacitor from pristine graphene-ink without using high-temperature processing or functional additives. The printable ink (89%) is formulated from pristine graphene without the addition of any functional additives. The symmetric flexible supercapacitor is demonstrated with an excellent specific capacitance of 137.50 F/g at 0.5 A/g and an energy density of 12.23 Wh/kg. The obtained gravimetric energy density beats reported earlier carbon-based supercapacitors that are 3D or inkjet printed. The flexibility and robustness of 3D-printed devices are achieved up to 150° folding angles. This work demonstrates an efficient and easy method for fabricating practical energy storage devices featuring a customizable shape and excellent flexibility.

This article presents recent advancements in the development of flexible piezoresistive strain sensors based on carbon nanotubes (CNTs)–polymer composites, with particular attention to their electromechanical properties. Various fabrication approaches and material preparation of CNTs–polymer composites with improved piezoresistive performance are introduced. Moreover, the article presents the working principle of the piezoresistive sensors in terms of the tunneling effect and disconnection-reconnection mechanism. The sensing performances of recently reported applications are studied. This work also reveals that the CNTs–polymer composites have great potential for flexible, skin-mountable, and wearable electronics applications. Finally, possible challenges for the future developments of CNTs–polymer composites are discussed.

레일장대화는 무도상교량의 소음, 진동, 충격 등의 문제점을 해결할 수 있는 경제적인 방안 중 하나이며, 최근 연동식 침목고정장치 를 이용한 SSF 공법이 개발된 바 있다. 이 연구에서는 연동식 침목고정장치 적용 시 레일 높이 조정 및 열차 통과 시의 충격 흡수를 목 적으로 교량침목 하부에 삽입되는 침목패드의 최적 연직강성을 결정하는 과정을 제시하였다. 침목패드의 최적 연직강성 결정을 위하 여 관련 기존 기준을 검토하였으며, 유연다물체동적해석을 통하여 침목패드의 연직강성 변화에 따른 주행안전성, 승차감 및 궤도의 안전성에 대한 지표들과 교량 응답 변화를 검토하였다. 유연다물체동적해석은 상용프로그램인 ABAQUS와 VI-Rail을 이용하여 수행 하였다. 수치해석은 30m 상로판형교에 대한 교량모델을 이용하여 수행하였으며, 침목패드의 연직강성이 7.5kN/mm ~ 240kN/mm로 변화할 때 ITX 새마을, KTX 및 화차 통과 시의 응답을 산정하였다. 수치해석에 적용된 궤도구성품 조건에서 침목패드의 최적 강성은 100kN/mm로 산정되었다.

Conductive carbon cloths (CCs) have been great attention as a promising current collector for flexible supercapacitors that supply power to portable and wearable electronics. However, the hydrophobic surface and weak adhesion with active materials has limited to be adopted as the binder-free and flexible electrode with mechanical/electrochemical stability. In this work, we demonstrate preparation of binder-free and flexible electrodes based on polyaniline (PANI) on carbon cloth. Polydopamine (PDA) layer are used to impart hydrophilicity, leading to uniform growth of PANI on the hydrophobic surface of carbon. Furthermore, PDA layer improves adhesion strength between PANI and carbon substrates, which allows for superior mechanical stability under ultrasonic condition. PANI-based flexible electrode shows high areal capacitance (160.8 mF cm− 2 at 0.5 mA cm− 2), good rate capability (71.1% even at high current density of 10 mA cm− 2), and long-term cycling stability (82.6% capacitance retention after 1500 cycles). Furthermore, a quasi-solid-state flexible supercapacitor reveals remarkable mechanical flexibility and durability, with superior capacitance retention (~ 100%) in bent state and after repetitive 1000 cycles.

본 연구는 유연근무제가 직원들의 직무열의에 미치는 영향을 분석하여, 유연근무제의 효과성을 분석하는 데에 목적을 두고 있다. 개인-환경 간의 적합성 이론(person-environment fit theory) 을 가반으로 하여, 유연근무제는 직원이 일과 삶의 균형을 이룰 수 있고 개인 생활의 요구를 충족 시키는 지원제도로서 이는 직원이 자신이 소속되어 있는 업무환경에 잘 적응하고 부합하도록 도울 것으로 기대할 수 있다. 따라서 본 연구는 유연근무제가 직원들의 직무열의에 미치는 긍정적인 영향력을 분석하고자 한다. 또한 본 연구는 유연근무제와 직무열의 간의 관계를 약화 또는 강화시키는 조절변수들의 영향력을 분석하고자 하는데, 그룹내 집단주의 문화와 제도적 집단주의 문화의 조절효과를 분석하였다. 실증분석을 위해, 본 연구는 보스턴대학의 Sloan센터에서 설문조사를 통해 수집한 “Generations of Talent Study” 데이터베이스와 GLOBE 데이터베이스를 사용하여 분석하였다. 미국, 영국, 중국, 인도, 브라질, 일본, 네덜란드, 멕시코와 스페인, 총 9국가에 위치한 다국적 기업에서 근무하고 있는 직원 7,701명의 설문 자료를 분석에 포함하였다. 분석결과, 유연근무제가 직원의 직무열의에 긍정적인 영향을 미치는 것으로 나타났다. 또한 그룹내 집단주의 문화가 유연근무제가 직무열의에 미치는 긍정적인 영향력을 약화시키는 결과가 밝혀졌다.

유연한 전기변색 소자(electrochromic device, ECD)는 스마트 윈도우 등 다양한 분야에서 응용이 기대되는 유망한 기술이다. 고분자 전해질은 유연한 ECD의 탈-변색 성능 및 물리적 안정성을 결정하는 중요한 구성요소이다. 본 연구에서는 효과적인 유연한 ECD 제조 및 내구성 향상을 위해 치수안정성이 우수한 세공충진 고분자 전해질 멤브레인(PFPEM)을 개발 하였다. 저렴하며 물리적 및 화학적 안정성이 우수한 폴리에틸렌 재질의 다공성 지지체의 세공에 접착력이 우수한 polyvinyl acetate와 이온전도도를 향상시킬 수 있는 polyethylene glycol을 사용하여 제조한 고분자 전해질을 충진하였다. 제조된 PFPEM의 최적 리튬 염(LiTFSI) 함량은 약 27 wt%에서 결정되었으며 우수한 치수안정성와 접착 강도 그리고 종래의 고분자 전해질에 근접하는 이온전도 특성을 가지고 있음을 확인하였다. 다공성 지지체의 사용으로 가시광 투과율이 저하되었으나 변색 상태에서는 오히려 장점으로 작용할 것으로 전망되었다.

Vertically Aligned Carbon Nanotubes (VACNTs)-coated flexible aluminium (Al) foil is studied as an electrode for supercapacitor applications. VACNTs are grown on Al foil inside thermal Chemical Vapor Deposition (CVD) reactor. 20 nm thick layer of Fe is used as a catalyst while Ar, H2 and C2H2 are used as precursor gases. The effect of growth temperature on the structure of CNTs is studied by varying the temperature of CVD reactor from 550 °C to 625 °C. Better alignment of VACNTs arrays on Al foil is recorded at 600 °C growth temperature in comparison to other processing temperatures. Cyclic voltammetry results shows that VACNTs-coated Al foil has a specific capacitance of ~ 3.01 F/g at a scan rate of 50 mV/s. The direct growth of VACNT array results in better contact with Al foil and thus low ESR values observed in impedance spectroscopy analysis. This leads to a fast charge–discharge cycle as well as a very high value of power density (187.79 kW/ kg) suitable for high power applications. Moreover, wettability study shows that the fabricated VACNT electrode has a contact angle of more than 152° which signifies that it is a superhydrophobic surface and hence shows lower specific capacitance in comparison to reported values for VACNT array. Therefore, it is necessary to develop suitable post-processing strategies to make VACNTs hydrophilic to realize their full potential in supercapacitor applications.

Electrochromic devices (ECDs) have been drawing great attention due to their high color contrast, low power consumption, and memory effect, and can be used in smart windows, automatic dimming mirrors, and information display devices. As with other electronic devices such as LEDs (light emitting diodes), solar cells, and transistors, the mechanical flexibility of ECDs is one of the most important issue for their potential applications. In this paper, we report on flexible ECDs (f-ECDs) fabricated using an all-in-one EC gel, which is a mixture of electrolyte and EC material. The f-ECDs are compared with rigid ECDs (r-ECDs) on ITO glass substrate in terms of color contrast, coloration efficiency, and switching speed. It is confirmed that the f-ECDs embedding all-in-one gel show strong blue absorption and have competitive EC performance. Repetitive bending tests show a degradation of electrochromic performance, which must be improved using an optimized device fabrication process.

Lightweight and flexible electromagnetic interference (EMI) shielding materials are in great demand for wearable EMI device. In the present work, lightweight and flexible carbon nanotube (CNT)/ferroferric oxide ( Fe3O4) composite film was made through a feasible chemical vapor deposition process for CNT film synthesis, followed by a hydrothermal reduction process for Fe3O4 coating. In the as-prepared composite, CNT film and Fe3O4 particles work as conductive skeleton and strong magnetic particle, respectively. The as-prepared composite film shows a novel EMI shielding effectiveness (SE) of 91 dB in the X-band, a small thickness of 0.09 mm and a low density of 0.86 g/cm3, which is superior to most of the carbonbased EMI materials.