MIT Scientists Discover Remarkable Light-Induced Evaporation Phenomenon
By David L. Chandler, Massachusetts Institute of Technology November 4, 2023
MIT scientists have made a groundbreaking discovery regarding the evaporation process. They have found that light can cause evaporation at a rate that surpasses that of heat alone, specifically in water bound by hydrogels. Termed the “photomolecular effect,” this finding could have profound implications for solar desalination and climate modeling by tripling water production in desalination processes and advancing solar cooling technologies.
This newfound process not only sheds light on various natural phenomena but also offers new possibilities for desalination approaches. It has puzzled scientists to observe that water held in hydrogels was evaporating at a much higher rate than could be explained by the thermal energy it received. The excess evaporation was notably significant, reaching double, triple, and even higher above the theoretical maximum rate.
Through a series of experiments and simulations, MIT researchers have come to a startling conclusion. Under specific conditions, at the interface between water and air, light can directly induce evaporation without the need for heat. What’s even more surprising is that light proves to be more efficient than heat in causing evaporation. While hydrogel-bound water was utilized in the experiments, the researchers believe that this phenomenon could occur under different conditions as well.
The findings of this study, conducted by MIT postdoc Yaodong Tu, Professor of Mechanical Engineering Gang Chen, and their team, are published in a paper in the Proceedings of the National Academy of Sciences (PNAS).
Lab experiments involved monitoring the surface of a hydrogel, which is primarily composed of water bound by a thin membrane lattice resembling JELL-O. The researchers tested its responses to simulated sunlight with controlled wavelengths. They discovered that evaporation rates varied depending on the color of light and reached their peak with green light. This color dependence, unrelated to heat, supports the theory that light is indeed the driving force behind the enhanced evaporation.
To confirm their hypothesis, the researchers attempted to replicate the observed evaporation rates using electricity to heat the material without employing light. However, the evaporation never exceeded the thermal limit in these tests, reaffirming that light was indeed responsible for the additional evaporation.
While water and hydrogel materials individually do not absorb significant amounts of light, their combined properties as strong absorbers allow for efficient utilization of solar photons, surpassing the thermal limit. This eliminates the need for dark dyes for absorption during the desalination process.
Implications and Ongoing Research
The discovery of this light-induced evaporation phenomenon, also known as the photomolecular effect, opens up promising opportunities for practical applications. The researchers have received grants from MIT’s Abdul Latif Jameel Water and Food Systems Lab and Bose Grant to explore the integration of this effect in solar-powered desalination systems and climate change modeling.
This breakthrough may revolutionize the desalination process. According to Tu, the typical desalination process involves two steps: evaporation of water into vapor and subsequent condensation to convert the vapor back into fresh water. With this newly found effect, the researchers anticipate achieving high efficiency in the evaporation stage, potentially tripling or quadrupling the current water production limit of 1.5 kilograms per square meter.
In addition to desalination, this phenomenon could have implications for various industrial processes that involve drying materials. It could also be utilized in evaporative cooling processes, enabling the development of highly efficient solar cooling systems.
The researchers are collaborating closely with other groups to replicate and validate their findings. Overcoming initial skepticism is crucial to establish the legitimacy of this unexpected discovery and the proposed hypothesis.
Reference
“Plausible photomolecular effect leading to water evaporation exceeding the thermal limit” by Yaodong Tu, Jiawei Zhou, Shaoting Lin, Mohammed Alshrah, Xuanhe Zhao and Gang Chen, 30 October 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2312751120
The research team includes Jiawei Zhou, Shaoting Lin, Mohammed Alshrah, and Xuanhe Zhao from MIT’s Department of Mechanical Engineering.
