THESIS
2021
1 online resource (xxiii, 141 pages) : illustrations (some color)
Abstract
Mechano-responsive nanocomposites are attractive for their capability to change the electrical,
optical, and chemical properties when external forces are applied, and are promising in emerging
applications such as stretchable electrodes and flexible displays. Because of the fabrication
difficulties to control the structure of materials, most studies have so far focused on exploiting
emerging materials to tailor the mechano-responsive behaviors while the role of material structures
remains largely unknown. However, with the development of micro/nano fabrication techniques
that allow building materials with well-defined architectures, a better understanding is now
available on structural effects. In this thesis, several design approaches are proposed to fabricate
ordered structures, and t...[
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Mechano-responsive nanocomposites are attractive for their capability to change the electrical,
optical, and chemical properties when external forces are applied, and are promising in emerging
applications such as stretchable electrodes and flexible displays. Because of the fabrication
difficulties to control the structure of materials, most studies have so far focused on exploiting
emerging materials to tailor the mechano-responsive behaviors while the role of material structures
remains largely unknown. However, with the development of micro/nano fabrication techniques
that allow building materials with well-defined architectures, a better understanding is now
available on structural effects. In this thesis, several design approaches are proposed to fabricate
ordered structures, and the relationship between the structure and the strain sensitivity of mechanoresponsive
nanocomposites is established. Based on the understanding of the relationships, the
sensitivities are carefully controlled to realize multidimensional strain sensing and high-contrast
optical modulation.
Anisotropic graphene aerogels are developed through unidirectional freeze-casting for in-plane
sensing. The aligned structure is found to endow the aerogel-based nanocomposites with strain
sensitivity highly dependent on loading directions. Combining this in-plane sensor with a pressure
sensor insensitive to lateral tension, the integrated sensor can differentiate mechanical stimuli
including in-plane tension, normal pressure, and shear, and presents an outstanding selectivity of 3.68 to in-plane strain directions. Based on such multidimensional sensing capability, a smart
device is demonstrated to monitor sports performance in real-time.
Periodic three-dimensional (3D) heterogeneous structure is fabricated by introducing modulus
mismatch between the two interdigitated phases. It is revealed that the strain concentrations at the
interfaces ameliorate the debonding at the interface to generate numerous nanogaps as light
scattering sites. The optimized light scatterer exhibits high transmittance modulation achievable at
a low strain of 15% and a remarkable maximum contrast of 82%. The same 3D heterogeneous
design strategy is successfully extended to improve the sensitivity of strain-induced coloration,
proving its wide applicability.
Inclined 3D porous structures are proposed from optical simulation and realized for the first
time by 3D patterning with a slanted exposure angle. Based on the structure, a novel light scatterer
is presented which changes from opaque to transparent under normal compression because of the
closing of the light-scattering pores. The pore closure is found to be facilitated when the pores are
inclined to the normal direction, resulting in the 3D inclined scatterer showing an unprecedentedly
high transmittance contrast of 96% and an extremely low lateral activation strain of ~1% for a
meaningful contrast. Such performance makes the scatterer highly promising for smart windows
with large sizes.
These results may open new horizons for the structural designs of mechano-responsive
nanocomposites that are practical in different application scenarios.
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