Researchers develop a new theory about the behavior of a new class of materials

Researchers led by Professor CEE Oscar Lopez-Pamies have derived the governing equations that describe and explain the macroscopic mechanical behavior of elastomers filled with liquid inclusions directly in terms of microscopic behavior. The work is described in an article by Lopez-Pamies and Ph.D. student Kamalendu Ghosh recently published in the Journal of Mechanics and Physics of Solids.

This work was carried out under the Lopez-Pamies grant from the National Science Foundation (NSF) program, Designing Materials to Revolutionize and Engineer our Future (DMREF). In turn, DMREF is part of the multi-agency Materials Genome initiative, which aims to pave the way for the discovery, manufacture and deployment of advanced materials.

“Since the discovery in the early 1900s that adding nanoparticles of carbon black and silica to rubber resulted in a composite material with dramatically improved properties, there has been continuous effort to understand when and how the addition of fillers to elastomers leads to materials with novel mechanical and physical properties,” Lopez-Pamies wrote. “The focus has been almost exclusively on solid filler inclusions.”

Recent theoretical and experimental results have revealed that instead of adding solid inclusions to elastomers, adding liquid inclusions can lead to an even more exciting new class of materials with the potential to enable a variety of new technologies. Some examples include elastomers filled with ionic liquids, liquid metals, and ferrofluids, which exhibit unique combinations of mechanical and physical properties.

“The reason for these new properties is twofold,” wrote Lopez-Pamies. “On the one hand, the addition of liquid inclusions to elastomers increases the overall deformability. This contrasts with the addition of conventional fillers which, being made of rigid solids, decrease the deformability. interfaces separating an elastomeric solid from encrusted liquid inclusions, although negligible when the inclusions are large, can have a significant or even predominant impact on the macroscopic response of the material when the particles are small.

“Strikingly, the equations establish that these materials behave like solids, albeit solids with macroscopic behavior that directly depends on the size of liquid inclusions and the behavior of elastomer/liquid interfaces. This allows access to an incredibly wide range of fascinating behaviors. by suitably adjusting the size of the inclusions and the chemistry of the elastomer/liquid interfaces. One of these remarkable behaviors is “masking”, when the effect of inclusions can be made to disappear.

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Materials provided by University of Illinois Grainger College of Engineering. Note: Content may be edited for style and length.

Sharon D. Cole