每年约有24万人因雷击而受伤。根据美国国家海洋和大气管理局（national ocean and atmospheric administration）的数据，在过去20年里，美国平均每年发生51起雷击死亡事故，位居第二，仅次于洪水造成的致命天气。
About 240,000 people are injured by lightning strikes each year. According to the National Oceanic and Atmospheric Administration, over the last 20 years, the United States averaged 51 annual lightning strike fatalities, placing it in the second position, just behind floods for deadly weather.
A single bolt of lightning carries a relatively large amount of energy. 5 billion joules over 10 microseconds is equal to 5×1014 (or 500 trillion) watts.
The mechanism behind lightnings is because water droplets became negatively charged from the contacts with other water droplets and ice in the clouds.
As the net charge in the droplets exceeds the air break-down charge density and come close to the ground, lightnings were produced.
What causes the water to gain a net charge from friction is the triboelectric effect (TE) which suggests materials become electrically charged after they were in contact with each other.
Triboelectric nano generators是由两层不同的介质膜面对面构成的，在叠层结构的上下表面分别沉积有电极。两个介电薄膜之间的物理接触产生了相反的带电表面。一旦两个表面在外力的作用下被一个小间隙隔开，就会产生一个电位降。
The triboelectric effect is very common in our lives but it’s also very unpredictable, so it is generally avoided in many technologies.
However, in recent years, nanogenerator is invented. It uses triboelectric effect to convert mechanical energy into electricity.
The TENG (Triboelectric Nanogenerators) consists of two dissimilar dielectric films face with each other, and there are electrodes being deposited on the top and the bottom surfaces of the stacked structure.
A physical contact between the two dielectric films creates oppositely charged surfaces. Once the two surfaces are separated by a small gap under the lifting of an external force, a potential drop is created.
If the two electrodes are electrically connected by a load, free electrons in one electrode would flow to the other electrode to build an opposite potential in order to balance the electrostatic field.
Once the gap is closed, the triboelectric charge created potential disappears, the electrons flow back.
Although we TE is a common phenomenon and there are technologies developed using such phenomenon, the fundamental mechanism of why two materials become charged once in physical contact.
Studies conducted by Professor Wang of the mechanism of the TE uses Kelvin probe microscopy. The Kelvin Probe microscopy has the ability of observing the work function of surfaces at atomic or molecular scales is important.
They use KPFM to observe the in different conditions between two dielectric, dielectric-metal and metal to metal. Their conclusion was that the TE “has to be an electron-dominated transition process”
In order to be able to more accurately model and predict lightnings, we need more information on the behavior of TE between two liquid material especially water molecules.
Professor Wang’s team using the concept of TENG to invent a new kind of nanogenerators which harvests directly from two liquid materials.
This Liquid-Liquid TENG (L-L TENG) is aiming at harvesting electricity from rain droplets.
It uses a frame built in with wires to hold a liquid membrane which collects rain droplets and therefore collects electrostatic electricity from the contact of rain droplets and the membrane.
The concept of this technology is key to understanding liquid to liquid material because it actually utilizes TE in between liquids which has not been possible in other methods.
Since insulators are more effective to hold electric charge than conductors, its ability and efficiency of performing TE is better.
Liquids such as water conducts electricity easily therefore it is hard to gain enough charge for TE to become significant. However, we know in extreme conditions of thunderstorms, the effect is quite significant to observe.
L-L TENG is a promise way of investigating into what conditions it has to have for lightning to occur. It collects charges from water drops from previous contact with air. Manipulating the volume of each droplet could change its surface area.
With a larger surface area, a droplet could have a larger charge density.
To model a thundercloud that produces lightning, information of the charge density of water droplets in the cloud is a requirement for knowing when exactly lightnings occurs.