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Ultra-High Elastic Strain Energy Storage in Metal-OxideInfiltrated Patterned Hybrid Polymer Nanocomposites Keith Dusoe, Xinyi Ye, Kim Kisslinger, Aaron Stein, Seok-Woo Lee, and Chang-Yong Nam Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.7b03238 • Publication Date (Web): 19 Oct 2017 Downloaded from http://pubs.acs.org on October 21, 2017
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Nano Letters
Ultra-High Elastic Strain Energy Storage in MetalOxide-Infiltrated Patterned Hybrid Polymer Nanocomposites Keith J. Dusoe1,*, Xinyi Ye2, Kim Kisslinger2, Aaron Stein2, Seok-Woo Lee1, Chang-Yong Nam2,* 1
Department of Materials Science and Engineering & Institute of Materials Science, University of
Connecticut, 97 North Eagleville Road, Unit 3136, Storrs, Connecticut 06269-3136, United States 2
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York
11973, United States *Corresponding author:
[email protected] (K.J.D.);
[email protected] (C.-Y.N.)
KEYWORDS: Elastic strain energy storage; infiltration synthesis; organic-inorganic hybrid nanocomposite; nanopillars; MEMS; resonator; actuator
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TABLE OF CONTENTS GRAPHIC:
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ABSTRACT
Modulus of resilience, the measure of a material’s ability to store and release elastic strain energy, is critical for realizing advanced mechanical actuation technologies in micro/nanoelectromechanical systems. In general, engineering the modulus of resilience is difficult because it requires asymmetrically increasing yield strength and Young’s modulus against their mutual scaling behavior. This task becomes further challenging if it needs to be carried out at the nanometer scale. Here, we demonstrate organic-inorganic hybrid composite nanopillars with one of the highest modulus of resilience per density, by utilizing vapor-phase aluminum oxide infiltration in lithographically patterned negative photoresist SU-8. In-situ nanomechanical measurements reveal a metal-like high yield strength (~500 MPa) with an unusually low, foam-like Young’s modulus (~7 GPa), a unique pairing that yields ultra-high modulus of resilience, reaching up to ~24 MJ/m3 as well as exceptional modulus of resilience per density of ~13.4 kJ/kg, surpassing those of most engineering materials. The hybrid polymer nanocomposite features lightweight, ultra-high tunable modulus of resilience and versatile nano-scale lithographic patternability, with potential for application as nanomechanical components which require ultra-high mechanical resilience and strength.
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TEXT The storage and release of elastic strain energy in materials, along with mechanical strength, play important roles in both natural and engineered mechanical actuation systems, including biological tissues responsible for the fast and high-powered locomotions in animals1,2 as well as highperformance micro/nanoelectromechanical systems (MEMS/NEMS) resonators and actuators3. Many emerging technologies also hinge on effective uses of mechanical energy storage and release, such as alternative energy systems4,5 and artificial muscles for robotic movements and motions6,7. Modulus of resilience (R) (unit: J/m3) measures the capacity to store elastic strain energy in materials per unit volume prior to the onset of plastic deformation.8 Normalizing R by density (ρ), the specific R (Rs) is also an important mechanical design parameter, representing the elastic strain energy storage capacity per weight (unit: (J/m3)/(kg/m3) = J/kg) in materials. To obtain an enhanced R in linear elastic solids, high yield strength (σy) and low Young’s modulus (E) in materials is desired, but engineering such a σy-E combination is highly challenging because both properties typically scale together.9 For example, metals and ceramics exhibit high σy and E, while polymers have both low σy and E. One system, among metallic systems, that achieves high R are bulk metallic glasses (BMG). Characterized by their amorphous structure, BMGs show ultra-high σy (> 2000 MPa) exceeding those in most materials but possess relatively low E (~100 GPa), comparable to those in typical metal alloys.10 This “high σy-low E” combination leads to an ultra-high R of ~20 MJ/m3 for Zr-based BMGs.10 BMGs are, however, heavy (ρ ~7000 kg/m3), making its Rs ~ 2.9 kJ/kg at best. They also show relatively low mechanical compliances (maximum elastic strain < 3%)10 and limited compatibility with nanofabrication processes necessary for producing nanomechanical components, such as those found in NEMS devices.
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Polymers, with naturally low ρ, represent promising starting material platforms for achieving high R and Rs because of their intrinsically low E. Some elastomers show a high capacity to store elastic energy among materials, but they exhibit low σy (500 MPa) and foam-like low E (
