Illuminating Evaporation: Unraveling the Photomolecular Effect

By: Sydney Hoffman  |  November 20, 2023

By Sydney Hoffman

Evaporation is a fundamental process in both natural and industrial contexts that has conventionally been understood as a consequence of thermal influence. Increased temperatures prompt heightened movement among water molecules in the liquid state, providing the extra energy needed to disrupt bonds between neighboring molecules, ultimately facilitating their release into the atmosphere as water vapor.

However, recent research from MIT challenges this traditional perspective by introducing a revolutionary concept known as the photomolecular effect. Led by MIT postdoc Yaodong Tu and Professor Gang Chen, the research team conducted experiments involving water held in hydrogels, structures with a high affinity for water absorption. This groundbreaking research proposes that, under specific conditions, light at the water-air interface can induce evaporation more efficiently than traditional heat-based methods, unveiling new possibilities for applications ranging from climate modeling to industrial processes.

In specific instances, the researchers observed that the evaporation rate surpassed expectations based on thermal energy alone, at times exceeding twice the anticipated level. Notably, according to Science News, the evaporation rate exhibited variability in relation to the wavelength of the light, with green light demonstrating the highest efficiency in inducing evaporation. These findings challenge conventional understandings of evaporation mechanisms and pave the way for innovative applications in diverse scientific and industrial fields.

The implications of this discovery extend across diverse fields. In climate modeling, the photomolecular effect may contribute to the formation and evolution of fog and clouds, urging its incorporation for enhanced model accuracy. Moreover, the industrial sector, particularly solar-powered desalination processes, stands to benefit significantly. By eliminating the need to convert sunlight to heat first, this discovery could revolutionize traditional desalination methods, making them more cost-effective.

The researchers identified a hue-specific phenomenon in their hydrogel experiments, observing that evaporation reached its zenith at a distinct wavelength of green light. This color-centric relationship, unrelated to heat, substantiates the proposition that light itself propels the observed excess evaporation. Intriguingly, the combination of water and hydrogel material, individually inefficient light absorbers, synergistically transforms into a potent absorber, enabling the effective utilization of solar photons and surpassing thermal constraints.

At present, the research team is actively exploring pragmatic applications of the photomolecular effect, with support from grants provided by MIT’s Abdul Latif Jameel Water and Food Systems Lab and a Bose Grant for climate change modeling. Their primary focus is on advancing the efficiency of solar-powered desalination systems, potentially obviating the necessity for a separate condensation step and thereby enhancing the cost-effectiveness of these processes.

In conclusion, this research challenges established notions about the driving forces behind evaporation and introduces the photomolecular effect as a new paradigm. As the scientific community explores and validates these findings, the potential applications of this discovery underscore its significance in shaping the future of water treatment, climate modeling, and industrial processes. The journey from understanding the fundamental interplay of light and water molecules to practical implementation, holds promise for transformative advancements in various scientific and technological domains.