Photo/electro-stimulated Charge Transfer in Triboelectric Nanogenerator

Department of Materials Science EngineeringWidespread energy harvesting, generating self-sufficient power from the surrounding environment, such as wind, solar and geothermal, have attracted increasing attention in the past decade due to the energy crisis and global warming. Among them, many technological devices converting mechanical energy into other forms of energy or vice versa have been proposed and investigated because of an extended life time, no recharging procedures, and their scalability. Generally, mechanical energy converted into electricity, namely, by using electromagnetic, electrostatic, and piezoelectric effects. Most recently, a new type of power generating device, named as triboelectric nanogenerator (TENG) based on triboelectric effects coupled with electrostatic effects have been demonstrated as powerful means of harvesting mechanical energy from living environment. Part 1. A simple fabrication route for ion gel nanofibers in a triboelectric nanogenerator was demonstrated. Using an electrospinning technique, we could fabricate a large-area ion gel nanofiber mat. The triboelectric nanogenerator was demonstrated by employing an ion gel nanofiber and the device exhibited an output power of 0.37 mW and good stability under continuous operation. Part 2. Understanding the charge transfer mechanism between two surfaces during the physical contact is crucial in the development of triboelectrification-related commercialized products. Here, we report that light illumination can reverse the direction of the charge transfer and significantly increase tribo-charge density occurring at the oxide/polyimide interface. Under light illumination, the surface potential maps of TiOx layer on P3HT:PC61BM/PEDOT:PSS/ITO substrate showed the significant decrease of the work function by approximately 0.2 eV, positioned to be at lower than that of the polyimide and thus increasing the work function difference with the polyimide. The wavelength-dependent measurement of the output open-circuit voltages revealed that the photogenerated electrons from active layer via visible light were accumulated at the surface of TiOx, enhancing the output short-circuit current of the triboelectric nanogenerator by 5 times, supported by the gate voltage-dependent output performance of the nanogenerator with TiOx/SiO2/Si substrate connected to the back gate metal. These results should help design improved energy harvesting devices as well as self-powered selective wavelength photodetectors.ope

Research Update: Recent progress in the development of effective dielectrics for high-output triboelectric nanogenerator

A new energy generating device, triboelectric nanogenerator (TENG), was discovered in 2012 and thereafter, many applications such as portable power sources and self-powered, appropriate for portable electronic devices. So far, rapid development of device fabrication technologies and mechanical system designs significantly increased the instantaneous output power up to several tens of mW/cm2. This article provides a comprehensive review of effective dielectrics used so far in TENGs for further enhancement in output power, as well as the fundamental issues regarding the materials. Finally, we show some strategies for obtaining the properties that the materials should have as effective dielectrics.ope

Association between supervisors’ behavior and wage workers’ job stress in Korea: analysis of the fourth Korean working conditions survey

Abstract Background In modern society, many workers are stressed. Supervisors’ support or behavior can affect the emotional or psychological part of the worker. The purpose of this study is to investigate the effect of supervisor’s behavior on worker’s stress. Methods The study included 19,272 subjects following the assignment of weighted values to workers other than soldiers using data from the Fourth Korean Working Condition Survey. Supervisors’ behavior was measured using 5 items: “supervisor feedback regarding work,” “respectful attitude,” “good conflict-resolution ability,” “good work-related planning and organizational ability,” and the encouragement of participation in important decision making. Job stress was measured using 1 item: “I experience stress at work.” Multiple logistic regression analysis was performed to examine the effects of supervisors’ behavioral, general, occupational, and psychosocial characteristics on job stress in workers. Organizational characteristics associated with supervisors’ behavior were also analyzed. Results The results showed that supervisors’ provision of feedback regarding work increased workers’ job stress (OR = 1.329, 95% CI = 1.203 ~ 1.468). When a supervisor respect workers (OR = 0.812, 95% CI = 0.722 ~ 0.913) or good at planning and organizing works (OR = 0.816, 95% CI: 0.732 ~ 0.910), workers’ job stress decreased. In particular, the two types of supervisor behaviors, other than feedback regarding work, were high in private-sector organizations employing less than 300 employees. Conclusion Supervisors’ behavior influenced job stress levels in workers. Therefore, it is necessary to increase education regarding the effects of supervisors’ behavior on job stress, which should initially be provided in private-sector organizations with up to 300 employees

Unprecedented colorimetric responses of polydiacetylenes driven by plasma induced polymerization and their patterning applications

We report for the first time that polydiacetylenes (PDAs) can be alternatively prepared via a plasma induced polymerization process. The degree of polymerization and colorimetric transitions could be manipulated by controlling the power of plasma radiofrequency, exposure time and by using an acrylic mask, resulting in their great potential for patterning applications.close1

Electrospun ion gel nanofibers for flexible triboelectric nanogenerator: electrochemical effect on output power

A simple fabrication route for ion gel nanofibers in a triboelectric nanogenerator was demonstrated. Using an electrospinning technique, we could fabricate a large-area ion gel nanofiber mat. The triboelectric nanogenerator was demonstrated by employing an ion gel nanofiber and the device exhibited an output power of 0.37 mW and good stability under continuous operation.close1

The migration of alkali metal (Na + , Li + , and K + ) ions in single crystalline vanadate nanowires: Rasch-Hinrichsen resistivity

We report the synthesis of single crystalline alkali metal vanadate nanowires, Li-vanadate (Li 4 V 10 O 27 ), Na-vanadate (NaV 6 O 15 ), and K-vanadate (KV 4 O 10 ) and their electrical properties in a single nanowire configuration. Alkali metal vanadate nanowires were obtained by a simple thermal annealing process with vanadium hydroxides(V(OH) 3 ) nanoparticles containing Li + , Na + , and K + ions and further the analysis of the migration of charged particles (Li + , Na + , and K + ) in vanadate by measuring the conductivity of them. We found that their ionic conductivities can be empirically explained by the Rasch-Hinrichsen resistivity and interpreted on the basis of transition state theory. Our results thus indicate that the Li ion shows the lowest potential barrier of ionic conduction due to its small ionic size. Additionally, Na-vanadate has the lowest ion number per unit V 2 O 5 , resulting in increased distance to move without collision, and ultimately in low resistivity at room temperature

Comparison of Cognitive Function between Patients with Restless Legs Syndrome and Healthy Controls

Background and Objective Studies regarding cognitive function in patients with restless legs syndrome (RLS) show inconsistent results, although comorbid psychiatric conditions including depression and anxiety are common in these patients. We compared cognitive performance and depression symptoms between drug-naïve RLS patients and healthy controls, in order to determine whether the depression symptoms that result from RLS affect cognitive function. Methods Drug-naïve RLS patients (n = 15) and age-matched controls (n = 17) were enrolled in the study. They completed clinical interviews, sleep questionnaires, and a neuropsychological assessment battery that measured multiple cognitive domains including attention, language ability, memory, and executive function. Depression was measured using the Beck Depression Inventory-II. Statistical analyses included chi-square and non-parametric Mann-Whitney U tests, and Spearman correlations. Results Restless legs syndrome patients performed better than controls on tests of verbal memory and category word fluency (animal) (p < 0.05). The RLS group had significantly higher depression scores than controls (p = 0.005). Depression scores for the RLS patients showed significant correlations with restless legs symptoms and several measures of sleep quality. There were no significant differences in cognitive function between patients with moderate to severe depression (n = 6) and those without depression (n = 6). Conclusions Our study did not confirm that symptoms of RLS were associated with cognitive dysfunction. In addition, depression symptoms had little impact on cognitive function, but were independently associated with symptoms of RLS regardless of cognitive function