Carbon nanotube–based magnetic actuation of origami membranes

Abstract

Multiwalled carbon nanotubes (CNTs) with nickel and cobalt catalyst tips have been grown on foldable titanium nitride membranes. Once magnetized to saturation under an external magnetic field, these ferromagnetic tips, which reside atop each CNT, can be used to actuate the entire membrane on which the nanotubes are grown. Magnetic modeling is performed to analyze the magnetic properties of the teardrop-shaped CNT tips, and initial experimental results show that magnetic torques and forces arising from the CNT tips are sufficient to rotate the membrane up to 180° and keep it latched without springing back.

Folding 2D Structures into 3D Configurations at the Micro/Nanoscale: Principles, Techniques, and Applications

“…Generally, the driving forces to activate the folding process can be either external (which is independent of the folding structure itself) or internal (which comes from the hinge part) as listed in Figure , and each strategy has a corresponding size scale. For external driving forces, the rigid parts can be actuated by a magnetic field, capillary force, compressive force, or cell traction force (CTF), where the hinge is only a flexible connection between the rigid parts, and the size of the as‐fabricated device is usually in the micrometer or millimeter scale. In comparison, for internal driving forces, the internal interactions within the hinge part can change its curvature and lead to folding of the rigid parts, which is sometimes referred to as “self‐folding.” The internal interactions could arise from surface tension (capillary force), material expansion/shrinking (strain gradient, phase transition in a shape memory polymer, pneumatic force), bio‐force (cell traction force), ion–solid interactions (focused ion beam), etc.…”

“…b) Scanning electron microscopy (SEM) images of unfolded and partially folded TiN membranes with Ni‐tipped CNTs. Reproduced with permission . Copyright 2008, AIP Publishing.…”

“…Alternatively, the magnetic plates can be replaced by other magnetized structures, e.g., carbon nanotubes (CNTs) with nickel and cobalt particles atop a TiN substrate (Figure b) . The nickel and cobalt particles act as catalyst materials for CNT growth, and on a single plate, there are hundreds of thousands of CNTs.…”

Three‐Dimensional Fabrication at Small Size Scales

“…There are numerous and diverse mechanisms that can be used to enable self‐folding. They include pneumatics,100, 101 magnetic forces,102–109 swelling of electroactive polymers,110–120 thermal and shape memory alloy actuation,121–128 ultrasonic pulse impact,130–133 muscular actuation,134, 135 stressed thin films,136–154 and surface forces 97, 98, 155–184. Notable traits of these methods are summarized in Table 1.…”

Driving microfluidic flows with three dimensional electrodes.

“…Self -folded structures can be fabricated with diverse mechanisms. These mechanisms include pneumatics ( [56], [57]) magnetic forces ( [58], [59]), swelling of electroactive polymers( [60], [61]), thermal and shape memory alloy actuation( [62], [63]), ultrasonic pulse impact [64], muscular actuation( [65], [66]), stressed thin film ( [67], [68], [69], [70] and [71]) and surface forces [72]. Reference [73] summarized the notable characteristics of these mechanisms in the table below.…”