THESIS
2022
1 online resource (xix, 114 pages) : illustrations (some color)
Abstract
Microcapsules containing functional liquid core materials are of great interest for the past
several decades. Developed encapsulation techniques have shown enormous potential in
designing novel intelligent materials used for food and cosmetic industries, self-healing and
self-cleaning composites, coatings, and construction. The organic or inorganic shell can
provide important protection for the liquid core material during manufacturing, processing,
transportation, and real applications. While the introduction of different types of core-shell
structured microcapsules as functional fillers can bring various promising functions to the
matrix material, it tends to decrease the strength and robustness of the matrix since majority of
artificial microcapsules are susceptible to deformation and...[
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Microcapsules containing functional liquid core materials are of great interest for the past
several decades. Developed encapsulation techniques have shown enormous potential in
designing novel intelligent materials used for food and cosmetic industries, self-healing and
self-cleaning composites, coatings, and construction. The organic or inorganic shell can
provide important protection for the liquid core material during manufacturing, processing,
transportation, and real applications. While the introduction of different types of core-shell
structured microcapsules as functional fillers can bring various promising functions to the
matrix material, it tends to decrease the strength and robustness of the matrix since majority of
artificial microcapsules are susceptible to deformation and failure. Moreover, the release of the
encapsulated liquid under certain loading conditions in its service life is a significant issue
worth considering.
In this thesis, the intrinsic mechanical parameters of the solid shell are successfully extracted
from single-microcapsule compression experiments based on related theories and numerical simulations. The deformation behaviors of a microcapsule under compression have been
investigated and influencing factors such as particle size, material properties, thickness ratio
and liquid core effect are reported to affect the structural response. Meanwhile, it is obvious
that the strength of a microcapsule is vital for its processing and applications. Different failure
modes and underlying mechanisms are revealed from compression experiments for three
categories of fabricated microcapsules (PS, PUF, ABS-shelled). Shell material properties,
strain rate, shell thickness ratio and shell microstructure are reported to greatly affect the failure
behaviors of microcapsules. Good agreements are found between numerical simulations and
experiments. Furthermore, microcapsules tend to suffer various types of loads including static
and dynamic during processing and applications. Since polymers usually utilized as shell
materials have a viscoelastic-plastic constitutive, time-dependent response of core-shell
microcapsules is studied through stress relaxation test and low cyclic fatigue test on PS
microcapsules. Reissner-Maxwell model is introduced to obtain the relaxation modulus.
Damage accumulation induced stiffness degradation and hysteresis resulted by viscoelasticity
until final stable state of a cyclically loaded microcapsule are analyzed.
The present research has endeavored to systematically investigate the mechanical behaviors
of core-shell microcapsules subjected to diversified external loads so as to have a more
comprehensive understanding of microcapsule mechanics and better guide the design,
fabrication, and applications of microcapsules.
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