Mechanics and Functionality of Extreme Mechanical Instabilities through Buckling Driven Delamination
Committee memberDarvish, Kurosh
Buckling Driven Delamination
Extremely Large Deformation
Thin Film/soft Substrate System
Permanent link to this recordhttp://hdl.handle.net/20.500.12613/3932
MetadataShow full item record
AbstractMechanical instabilities such as wrinkling and buckling-driven delamination in thin film-substrate systems have historically been considered as one of structural failure mechanisms, which should be avoided. The past decade has witnesssed rapid growth in harnessing such surface instabilities for a wide range of tunable surface related properties and functionalities, especially in soft materials on small scales. Compared to extensively studied wrinkling on soft substrates and localized buckling driven delamination on stiff substrates, the fundamental mechanics underpinning ordered buckle-delamination on soft substrate over large area and its guidance for potential implications in engineering innovation remain largely to be explored. This thesis aims to partially bridging such a knowledge gap. In this thesis, I exploit how to generate the controllable and globally periodic delaminated buckling patterns in thin films on highly prestrained elastomeric substrates, and then explore the fundamental mechanics of this spontaneous extreme buckling driven periodic delamination, as well as its implications in design of extremely stretchable electronics and interfacial mechanical properties measurement. Compared to wrinkling, one of the benefits of extremely buckling driven delamination is the extraordinarily high aspect ratio of buckles. The large surface roughness and high local curvature could potentially enable extreme surface topographies related properties, such as adhesion, wetting, friction, and optics, as well as augment the extreme stretchability in stretchable optical and electronic devices. In the aim of harnessing this extreme buckling driven delamination, I first explore the formation and evolution of extraordinarily high-aspect-ratio delaminated buckles of thin films on 400% pre-strained elastomers, as well as uncovered the underlying deformation mechanism through combining quantitative theoretical analysis and experimental and numerical approaches. A theoretical framework is developed to describe the formation and evolution process of periodic delaminated buckles, which includes three deformation stages, i.e. onset of localized blisters (Stage I), growth and propagation of delamination (Stage II), and post-buckling after delamination arrest (Stage III). I show that under extreme large compressive strain, the profile of periodic blisters changes from sinusoidal shape to jig-saw-like shape with relative high aspect ratio, which have potential applications for design of extremely stretchable electronics. Equipped with the fundamental mechanics of buckle-delamination in thin films, I then exploit harnessing the spontaneous buckling driven periodic delamination to achieve high stretchability in both metal and silicon films. Experimentally I observe periodic buckle-delaminated patterns over large area, accompanied by highly ordered transversely cracking patterns, which can be theoretically predicted by simple crack fragments model. I hypothesize that when the width of ribbons is set to be equal or smaller than the theoretically predicted crack fragment width, there would be no cracking fragmentation. This criteria for designing crack-free micro-ribbons is further validated by related experiments. Guided by the validated criteria, I successfully design crack-free and spontaneous delaminated ribbons on highly prestrained elastomer substrates, which provides a high stretchability of about 120% and 400% in Si and Au ribbons, respectively. I further extend the buckling instability-based metrology to systematically measure the mechanical properties of 2D organic conjugated polymer nano-films, which have tremendous promising applications in organic integrated circuits, solar cells, and stretchable devices. I develop a new fabrication strategy to generate buckle-delaminated free-standing organic conjugated polymeric (P3BT/C60) nanosheets. Through both experiments and theoretical analysis, I show that the free-standing buckle-delaminated organic P3BT/C60 nanosheets have significant advantages over the traditional spin-coated wrinkled nanosheets, including the enhanced mechanical properties, a higher level of stretchability with lower electrical resistance, and a wider range of controllable wettability modulation.
ADA complianceFor Americans with Disabilities Act (ADA) accommodation, including help with reading this content, please contact firstname.lastname@example.org
Showing items related by title, author, creator and subject.
Concept Mapping as a Mechanism for Assessing Science Teachers’ Cross-Disciplinary Field-Based LearningGarner, Joanna K.; Kaplan, Avi; Hathcock, Stephanie; Bergey, Bradley W.; 0000-0002-2898-0085 (2019-07-11)Two common goals of science teacher professional development (PD) are increased content knowledge (CK) and improved readiness to teach through inquiry. However, PD assessment challenges arise when the context is structured around inquiry-based, participant-driven learning, and when the content crosses scientific disciplines. This study extended the use of concept mapping as an assessment tool for examining changes in the content knowledge of 21 high school science teachers who participated in a field-based environmental science summer institute. The scoring rubric focused on documenting concepts, links, and map organization and scope in an attempt to capture development of cross-disciplinary knowledge in ways that correspond with theories of expertise development. The analysis revealed significant gains from pre-PD to post PD maps in the sophistication of links between concepts and in the number of additional, participant-generated scientifically valid concepts. Relative to the initial maps, post PD maps also manifested more complete clustering of concepts. Findings are discussed in reference to previous studies on teachers’ learning and implications for future research using concept mapping as a means of assessing teacher PD.
MECHANISMS OF G PROTEIN-COUPLED RECEPTOR 2 REGULATION AND INHIBITION IN CARDIOVASCULAR DISEASE AND AGINGKoch, Walter J; Houser, Steven R.; Kishore, Raj; Drosatos, Konstantinos; Sato, Priscila (Temple University. Libraries, 2020)G protein-coupled receptor kinase 2 (GRK2) has been a thriving therapeutic target for cardiovascular disease treatment since its discovery for desensitizing and downregulating b-adrenergic receptors that are vital to cardiac function. GRK2 inhibition through a variety of methods in animal models of cardiac ischemia and heart failure achieved improvements in cardiac function, hemodynamic function, cardiomyocyte apoptosis, and fibrotic scar size among many other observations. Although GRK2 has been used as a therapeutic tool in multiple studies, its mechanisms of regulation are necessary to understand its role in disease pathogenesis and therapeutic application. This dissertation comprises two projects (1) investigating the microRNA (miRNA) regulation of GRK2 and (2) investigating the impact of loss of dynamic regulation of GRK2 through S-nitrosylation. (1) Candidate miRNAs were selected from miRNA microarray analysis of miRNA differential expression data and bioinformatic prediction. In vitro validation of kshv-miR- K12-3-5p and hsa-miR-181a-5p have shown their ability to bind to the GRK2 3’UTR as well as significantly decrease GRK2 mRNA or protein. The successful regulation of GRK2 through these miRNAs warrant in vivo application and investigation as GRK2-targeting HF therapy in a mouse model of HF. (2) In order to determine the impact of chronic GRK2 overactivity, mice that contained a knock-in mutation of GRK2 Cys340àSer (GRK2- C340S), a site of dynamic inhibitory regulation by S-nitrosylation, were allowed to age >12 months. Loss of S-nitrosylation of GRK2 was sufficient to cause cardiovascular remodeling and dysfunction over time.
THE MOLECULAR MECHANISMS OF THE EFFECTS OF C-CBL ON CYTOSKELETON-MEDIATED PHENOMENATsygankov, Alexander (Temple University. Libraries, 2008)c-Cbl functions as a multifunctional adaptor and an E3 ubiquitin protein ligase. Several studies have shown that c-Cbl is involved in cytoskeleton-mediated events, but the molecular mechanisms linking c-Cbl to cytoskeletal rearrangements remain to be elucidated. Our previous results indicated that c-Cbl facilitates spreading and migration of v-Abl-transformed NIH 3T3 fibroblasts and suggested that small GTPases play important roles in the cytoskeletal effects of c-Cbl in this system. To elucidate the individual contributions of small GTPases to these effects, we assessed the roles of endogenous Rac1, RhoA and Rap1 in the c-Cbl-dependent spreading and migration of v-Abl-transformed fibroblasts overexpressing c-Cbl, using RNAi. Furthermore, since it has been shown that Rap1 can act as an upstream regulator of Rac1 in inducing cell spreading, we analyzed the interplay between Rap1 and Rac1 in the signaling pathways connecting c-Cbl to the cytoskeletal events. Our results indicate that Rac1 is essential for cell migration and spreading, whereas activation of RhoA exerts a negative effect. We have also shown that Rap1 is essential for cell spreading, although not for migration in our experimental system. Furthermore, we provide evidence that Rap1 is located upstream of Rac1 in one of the signaling pathways that regulate c-Cbl-facilitated cell spreading. Overall, our findings are consistent with the model describing the connection of c-Cbl to the cytoskeletal rearrangements via two pathways, one of which is mediated by PI3K and Rac1, and the other, by CrkL/C3G, Rap1 and Rac1. A major biological feature of glioma is the ability to invade normal brain tissue. The molecular mechanisms of glioma invasion are involved in multiple biological processes which are primarily associated with cytoskeleton-mediated events including adhesion, migration, degradation of extra cellular matrix (ECM). Biological functions of c-Cbl in glioma have not been elucidated. In this study, we examined biological roles of c-Cbl using RNAi-mediated depletion of endogenous c-Cbl and stably c-Cbl expressing glioma cells generated by lentiviral transduction and showed that c-Cbl increases invasion through degradation of ECM by upregulation of MMP2 but not through migration, adhesion, or growth of SNB19, a grade IV glioblastoma cell line.