Researchers Develop Mutating Crystals Using Water Evaporation

Water evaporation, as seen when a pool of water vanishes on a summer day, is a truly astonishing and powerful process. If it were harnessed, the process could offer a clean source of energy to operate mechanical machines and various devices.

In a newly issued paper in the journal Nature Materials, an international team of researchers led by scientists at the Advanced Science Research Center at the Graduate Center, CUNY (CUNY ASRC) explains the development of shape-changing crystals that directly transform evaporation energy into powerful motions.

Harvesting Evaporation Energy

These water-responsive materials were designed by employing simple versions of biological building blocks, known as tripeptides​, to create crystals that are stiff and morphable at the same time.

The materials are made of three-dimensional patters of nanoscale pores in the place where water tightly binds, and these pores are interspersed with a molecular network of both rigid and flexible areas. When humidity is lowered and gets to a critical level, the water gets our of the pores, which leads to a powerful compression of the interconnected system.

This ends up in the crystals temporarily losing their organized patterns until the humidity is restored, and the crystals get back their original shape. This newly created process can be repeated again and again and gives rise to an incredibly efficient technique of harvesting evaporation energy in order to perform mechanical work.

“We essentially created a new type of actuator, which is driven by water evaporation,” said Graduate Center Ph.D. student Roxana Piotrowska, the study’s first author and a researcher at the CUNY ASRC Nanoscience Initiative. “By observing its activity, we’ve been able to identify the fundamental mechanisms of how water-responsive materials can efficiently convert evaporation into mechanical energy.”

Researchers have developed tripeptide crystals, which feature aqueous pores that expand and contract in response to humidity changes and use evaporation to create an effective mechanical actuator. [Image Credit: Tony Wang]
“Our work enables the direct observation of materials’ evaporation-driven actuation at the molecular scale,” said the study’s corresponding author Xi Chen, whose lab, with CUNY ASRC Nanoscience Initiative, co-led the research. “By learning how to efficiently extract energy from evaporation, and turn it into motion, better and more efficient actuators can be designed for many applications, including evaporation energy harvesting devices.”

Powered by Water Evaporation

“Importantly, our designed crystals are produced from the exact same building blocks that proteins are made of, but they are radically simplified, and as a result, their properties can be precisely tuned and rationally optimized for this application,” said CUNY ASRC Nanoscience Initiative Director Rein Ulijn, whose laboratory, which co-led the study, is responsible for the biomolecular design parts of the research. “The beauty of using biological building blocks to create this new technology is that the resulting morphogenic crystals are biocompatible, biodegradable, and cost-effective.”

By employing a mix of laboratory-based experiments and computer simulations, the team of scientists was able to detect and analyze the factors that manage the actuation of these crystals.

This method resulted in new information, and therefore, understanding that passed on the design to know of more effective methods to use evaporation for a number of applications, which may include robotic parts or mechanical micro- and nano-machines that are operating on water evaporation.

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