A new framework for building responsive gels with programmed properties opens the door to advancements in energy devices, actuators and nano-filtration systems, say researchers at Caltech
Unraveling the Mysteries of Metallo-Polyelectrolyte Complexes
Metallo-polyelectrolyte complexes (MPECs) are a novel type of soft polymer that can undergo remarkable changes in their properties by exposure to different stimuli. Such materials, which possess both the properties of electrolytes and those of regular polymers, have captivated scientists for decades.
Until now, scientists had discovered and created some MPECs with weird characteristics in the materials, but their origins remained elusive. Now, combining laboratory experiments, computational work, and additive manufacturing (3D printing), the Caltech team has created a complete framework to examine MPECs from single molecule behaviour to overall material properties.
The ultimately reversible character of the ions is at the heart of what makes MPECs so mutable, with metal ions in their cores forming loose, dynamic ionic bonds to polymer chains. The scientists could tailor the properties of these materials by varying factors such as the metal’s valency, and pH of solution and solvent, which expanded their potential functions.
Transformative Potential: From Self-Monitoring Filters to Artificial Muscles
The results of the Caltech study carry broad implications. These materials, however, can possess a variation of properties and responses based on what design choice is made according to Julia R. Greer, the senior author.
This, for instance, enabled the researchers to create a polymer that behaves like muscular human tissue — or when heated caused a flower configuration in the bloom and then revert back to form a closed bud. The valency of the metal ion determined the rate and extent to which this transformation occurred, showing how precise control could be exerted.
In one other experiment, the researchers made a gel strip with one side of high pH and the other of low pH. Immersed in various solutions, the strip deformed predictably — demonstrating that these materials could be used as autonomous filters that could self-monitor their efficacy, advanced ion-exchange membranes and even artificial muscles.
Conclusion
The work by the Caltech team lays down a complete blueprint for designing and tuning responsive gels with desired functions and mechanical performances, he adds. Based on this knowledge of how molecular-level interactions lead to the collective behaviour of materials, researchers have a new set of tools to explore many challenging technologies in diverse applications ranging from energy devices to artificial muscle actuators.
