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Title:Strain responsive systems based on deformed low dimensional materials for sensing and actuation
Author(s):Snapp, Peter M.
Director of Research:Nam, SungWoo
Doctoral Committee Chair(s):Nam, SungWoo
Doctoral Committee Member(s):Park, Cheol; Kim, Seok; Cai, Lili
Department / Program:Mechanical Science and Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):crumpled graphene
photonic crystal
strain gauge
boron nitride nanotubes
strain alignment
glassy layers
transverse buckling
localized crumpling
mated graphene channels
Abstract:Low dimensional materials such as two dimensional (2D) graphene and one dimensional (1D) boron nitride nanotubes (BNNTs) have demanded the attention of the scientific community as a result of their fascinating electrical, optical, mechanical, and thermal properties. Unfortunately, efficient integration of low dimensional materials into complete, three dimensional (3D) systems remains a significant challenge. Application of strain has emerged as a key technique to deform low dimensional materials’ structure, easing their integration into larger devices and tuning their properties. Application of a compressive strain to graphene results in reversible crumpling of the graphene layer, increasing stretchability and forming complex out-of-plane structures. Similarly, tensile strain can be applied to disordered networks of BNNTs to drive alignment, enhancing strength and electromechanical response. Thin films also respond to applied deformation distinctly from bulk materials, experiencing enhanced out-of-plane buckling as a result of strain which tunes interaction with light and wetting fluids. We have sought ways to leverage deformed low dimensional materials to generate systems for sensing and actuation. First, we developed a stretchable phototransducer with enhanced and strain‐tunable photoresponsivity based exclusively on crumpled/buckled 3D graphene structures. By increasing graphene's areal density via contractile buckling, we achieved a more than an order‐of‐magnitude enhancement in graphene’s optical extinction, which led to an ~400% enhancement in photoresponsivity. Furthermore, we demonstrated the new concept of strain‐tunable photoresponsivity, showing a 100% modulation in photoresponsivity by applying strains up to 200%. This stretchable crumpled graphene sensor with enhanced and tunable photoresponsivity, has future potential for integrated biomedical optical sensing systems. As an extension of our crumpled graphene optomechanical sensor work, we developed a colorimetric strain sensor with optoelectrical quantification based on a hybrid system of colloidal photonic crystals (CPCs) over a crumpled graphene phototransducer. Transmission of incident light is modulated by the strained CPC layer and the modulated light is electrically quantified by the crumpled graphene phototransducer. The hybrid system enables direct visual perception of strain, via the color changing CPC, while strain quantification, via electrical measurement of the illuminated crumpled graphene phototransducer, outperforms that of unilluminated crumpled graphene strain sensors by more than 100 times. The unique combination of a photonic sensing element with a deformable transducer will allow for the development of novel, electrically quantifiable colorimetric sensors with high sensitivity. Transitioning focus away from 2D graphene, 1D BNNTs offer properties distinct from 2D materials. We produced multifunctional, stretchable BNNT/PDMS composites, using a co-solvent blending method with tetrahydrofuran (THF) to disperse BNNTs in PDMS without functionalization or sonication. Composites demonstrated augmented Young’s modulus (200% increase at 9 wt% BNNT) and thermal conductivity (120% increase at 9 wt% BNNT) without losing stretchability. Furthermore, BNNT/PDMS composites demonstrated piezoelectric responses which were linearly proportional to BNNT wt%, achieving a piezoelectric constant (|d33|) of 18 pmV-1 at 9 wt% BNNT. Uniquely, BNNT/PDMS accommodates tensile strains up to 60%, aligning BNNTs and enhancing the composites’ piezoelectric response ~5 times. Finally, the combined stretchable and piezoelectric nature of the composite was exploited to produce a vibration sensor sensitive to low frequency (~1 kHz) excitation and enables applications in soft actuators and smart materials. Finally, interesting opportunities exist in exploiting the dynamic behavior of textured 2D materials and thin films as strain is applied. We locally crumpled graphene channels with cracked glassy underlayers to produce strain sensors with deformation memory. As locally crumpled graphene supported on cracked glassy layers is stretched, the glassy islands distributed across the surface beneath the graphene begin to transversely buckle as a result of Poisson’s ratio driven contraction. In mated systems, this transverse buckling drives layers apart, leading to clean, continuous shifts in interfacial electrical resistance with strain. Furthermore, interfacial rearrangement is semi-permanent, leading to non-volatile changes in electrical resistance, allowing mated channels to serve as strain memory sensors. Mated channels show permanent shifts in resistance after threshold strains allowing channels to be used as strain memory sensors. Additionally, the instantaneous gauge factor (Gf) of mated channels experiences large jumps in value as sensors exceed the maximum previously applied strain, allowing for tuning of the threshold strain at which strain sensors will experience resistance jumps. Finally, these memory effects are tunable with the glassy skin thickness allowing for the production of strain sensors with optimized memory characteristics. In conclusion, we have reported novel systems that exploit deformation to integrate low dimensional materials into functional 3D systems while enhancing their inherent properties. We believe our approach of deforming low dimensional materials to achieve advanced functionality contributes to the larger research community, demonstrating methods to realize the potential of isolated low dimensional materials at the macroscale while enhancing their robustness and enabling new properties. With this approach, it is possible to achieve advanced sensors and actuators based on low dimensional materials with ease.
Issue Date:2020-10-26
Rights Information:© 2020 by Peter Snapp. All rights reserved
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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