Theory of electrocaloric effect in a shape-changing container: gas in a nanotube.

Driven by applied voltage or Ohmic heating, bistable nanotubes filled with gas can transform between expanded and collapsed configurations and by doing so convert energy between mechanical, electrical, and thermal forms. The electrocaloric response, a reversible change of temperature in response to applied voltage, combines the advantages of a working fluid with the lack of internal interfaces characteristic of robust solid-state thermoelectric devices. Such devices could be constructed from any conductive two-dimensional atomically thin material wrapped into an appropriate geometry.

Theory of carbomorph cycles.

We present a theory of a reversibly deforming sp2-carbon-based system controlled by competing strain, surface, and electrostatic energies, a carbomorph. For example, external forces (such as electrostatic, chemical, interfacial) could convert a bistable carbon nanotube between the collapsed and inflated states. Such a system could operate as a voltage-controlled constant-force spring, a charge-controlled harmonic spring, or an electromechanical engine or generator (with linear stroke up to few microns) driven across a propagating quasi-one-dimensional structural phase transition.

Modeling electrostatically induced collapse transitions in carbon nanotubes.

Molecular dynamics simulations demonstrate how a mechanically bistable single-walled carbon nanotube can act as a variable-shaped capacitor. If the voltage is tuned so that collapsed and inflated states are degenerate, the tube's susceptibility to diverse external stimuli--temperature, voltage, trapped atoms--diverges following a universal curve, yielding an exceptionally sensitive sensor or actuator. The boundary between collapsed and inflated states can shift hundreds of angstroms in response to a single gas atom inside the tube.

Lost Mold Rapid Infiltration Forming of Mesoscale Ceramics: Part 1, Fabrication.

Free-standing mesoscale (340 mum x 30 mum x 20 mum) bend bars with an aspect ratio over 15:1 and an edge resolution as fine as a single grain diameter ( approximately 400 nm) have been fabricated in large numbers on refractory ceramic substrates by combining a novel powder processing approach with photoresist molds and an innovative lost-mold thermal process. The colloid and interfacial chemistry of the nanoscale zirconia particulates has been modeled and used to prepare highly concentrated suspensions. Engineering solutions to challenges in mold fabrication and casting have yielded free-standing, crack-free parts.

Lost Mold-Rapid Infiltration Forming of Mesoscale Ceramics: Part 2, Geometry and Strength Improvements.

Iterative process improvements have been used to eliminate strength-limiting geometric flaws in mesoscale bend bars composed of yttria-tetragonal zirconia polycrystals (Y-TZP). These improvements led to large quantities of high bend strength material. The metrology of Y-TZP mesoscale bend bars produced using a novel lost mold-rapid infiltration-forming process (LM-RIF) is characterized over several process improvements.

Carbon nanostructures as an electromechanical bicontinuum.

A two-field model provides a unifying framework for elasticity, lattice dynamics and electromechanical coupling in graphene and carbon nanotubes, describes optical phonons, nontrivial acoustic branches, strain-induced gap opening, gap-induced phonon softening, doping-induced deformations, and even the hexagonal graphenic Brillouin zone, and thus explains and extends a previously disparate accumulation of analytical and computational results.