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Full-Text Articles in Engineering Science and Materials

Grain-Boundary Kinetics And Nonequilibrium Grain-Boundary Structure, Jian Han Jan 2018

Grain-Boundary Kinetics And Nonequilibrium Grain-Boundary Structure, Jian Han

Publicly Accessible Penn Dissertations

Microstructure of polycrystalline materials can be described as grain boundary (GB) networks; hence, GBs play major role in a wide-range of polycrystal properties. Control over GB kinetics provides effective means to tailor polycrystal properties through material processing. Understanding and prediction of GB kinetic behavior are always central problems in materials science. In this thesis, these are realized based on a mechanistic model. The mechanistic model describes a GB as intrinsic GB structure decorated by extrinsic defects. GB kinetics is described by the transition among all the stable/metastable intrinsic GB structures and the kinetics of GB defects. A major type ...


Controlled Folding In Precisely Functionalized Polyethylenes: Designing Nanoscale Lamellar Structures For Ion Transport, Edward Boynton Trigg Jan 2018

Controlled Folding In Precisely Functionalized Polyethylenes: Designing Nanoscale Lamellar Structures For Ion Transport, Edward Boynton Trigg

Publicly Accessible Penn Dissertations

There is great societal need for improved energy storage technology, in applications ranging from electric vehicles to grid storage to emergency power systems. New polymeric membranes with enhanced ion conductivities are needed in batteries and fuel cells to improve these technologies. Despite decades of research, these membrane materials are still not adequate for commercial use. The primary metric that requires improvement is ion or proton conductivity of the membrane under desirable operating conditions.

Modifying linear polyethylene by the addition of precisely periodic functional groups leads to a rich array of intriguing morphologies and properties. Depending on the functional group chemistry ...


The Role Of Sliding Contact In Nanoscale Tribochemistry, Zachary Banks Milne Jan 2018

The Role Of Sliding Contact In Nanoscale Tribochemistry, Zachary Banks Milne

Publicly Accessible Penn Dissertations

In this dissertation, the results of experimental and theoretical studies exploring friction

and adhesion at the nanoscale are presented. Using a customized in situ transmission

electron microscopy nanoindentation methodology, it is observed that cohesion of silicon and

adhesion of silicon and diamond are strongly modied by the sliding speed and the normal

stress applied during sliding. This indicates that shear stress modulates the reactivity of the

surfaces. This is the rst time that tunable adhesion of hard contacts has been demonstrated

in situ.

If sliding experiments are performed in ultra-high vacuum and the interfacial shear stress

is low enough to ...


Atomic Force Microscopy-Based Investigation Of Plastic Deformation Mechanisms In Disordered Nanoparticle Packings, Joel Allen Lefever Jan 2018

Atomic Force Microscopy-Based Investigation Of Plastic Deformation Mechanisms In Disordered Nanoparticle Packings, Joel Allen Lefever

Publicly Accessible Penn Dissertations

Understanding the plastic deformation mechanisms of disordered materials is a longstanding and complex problem in condensed matter physics and materials science. In particular, the elementary plastic rearrangement in a disordered material is believed to be the shear transformation zone, a localized cooperative motion of a handful of constituents. Although observed in mesoscale systems, the shear transformation zone has never been identified in an experiment at the nanoscale. In the present work, atomic force microscopy is used to probe the mechanical response of thin films of disordered nanoparticle packings that have been deposited by spin-coating and layer-by-layer deposition. Results demonstrate that ...