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Boosting Chemical Actuators by Architecture: Towards High Energy Capacity Artificial Muscles

Abstract:

Polymeric artificial muscles are great candidates to replace traditional rigid actuators due to their lightweight nature and high actuation stroke. However, the actuation mechanism of most polymer artificial muscles often relies on large temperature changes which may cause polymer degradation. Besides, having detectable thermal IR signals is not suitable for some applications. Chemical stimulants, on the other hand, can operate polymer artificial muscles and address these limitations. In this presentation, the actuation response of athermal pH-responsive artificial muscles made of aligned and coiled fibers will first be presented as a function of their processing parameters. We then show our recent results which demonstrate that a coiled architecture can be utilized to simultaneously amplify actuation stroke and work capacity by benefitting from the anisotropic length and diameter changes of individual fibers in response to pH changes. Our coiled pH-responsive fibers can deliver up to 43% contractive actuation stroke. The maximum obtained work capacity of 393 J/kg is 5 times higher than that of the aligned fiber counterpart. At an actuation of 22%, the polymer muscle lifts weight over 2000 times heavier relative to its own weight. A mechanistic model of coiled fibers revealed that the amplification of stroke and work capacity are owed to significant changes in the bending and torsional stiffness stemming from the changes in elastic modulus and fiber diameter.  

Bio: 

Dr. Mohammad Naraghi received his PhD degree in 2009 from the University Illinois at Urbana Champaign, Department of Aerospace engineering. His PhD research was in the field of nanomechanics and the application of MEMS sensors and actuators to investigate the mechanical behavior of soft nanofibers. His PhD thesis received the “Roger A. Strehlow Memorial Award”, for outstanding research accomplishments. Next, Dr. Naraghi worked as a post-doctorate research fellow at Northwestern University. He then joined Texas A and M university, department of Aerospace engineering, as an assistant professor, where he was promoted to the rank of associate professor with tenure in 2018. He is also affiliated with the department of Materials Science and Engineering. He is the director of the Multifunctional Nanomaterials lab. Dr. Naraghi’s main field of expertise is high performance light-weight nanocomposites, nanomechanics, mechanical characterization of soft nanostructures and soft actuators, and application of MEMS to nanomechanics. Naraghi is the recipient of several academic and scientific awards including the AFOSR YIP award in 2014 and AFRL summer faculty fellow in 2020. His research has been funded by several agencies, including Air Force Office of Scientific Research, Office of Naval Research, National Science Foundation, Army Research Lab, Army Research Office, Air Force Research Lab and Qatar National Research Funds, as well as private sector.