Spontaneous assembly of carbon-based chains in polymer matrixes through surface charge templates

Dielectrophoretic alignment of carbon nanotubes: theory, applications, and future

Carbon nanotubes (CNTs) are nominated to be the successor of several semiconductors and metals due to their unique physical and chemical properties. It has been concerning that the anisotropic and low controllability of CNTs impedes their adoption in commercial applications. Dielectrophoresis (DEP) is known as the electrokinetics motion of polarizable nanoparticles under the influence of nonuniform electric fields. The uniqueness of this phenomenon allows DEP to be employed as a novel method to align, assemble, separate, and manipulate CNTs suspended in liquid mediums. This article begins with a brief overview of CNT structure and production, with the emphasize on their electrical properties and response to electric fields. The DEP phenomenon as a CNT alignment method is demonstrated and graphically discussed, along with its theory, procedure, and parameters. We also discussed the side forces that arise in DEP systems and how they negatively or positively affect the CNT alignment. The article concludes with a brief review of CNT-based devices fabricated using DEP, as well as the method's limitations and future prospects.

Pyro-Electrification of Freestanding Polymer Sheets: A New Tool for Cation-Free Manipulation of Cell Adhesion in vitro

Localized electric fields have become, in recent years, a source of inspiration to researchers and laboratories thanks to a huge amount of applications derived from it, including positioning of microparticles as building blocks for electrical, optical, and magnetic devices. The possibility of producing polymeric materials with surface charge thus opens new perspectives for applications where process simplicity and cost-effectiveness of flexible electronics are of fundamental importance. In particular, the influence of surface charges is widely studied and is a critical issue especially when new materials and functional technologies are introduced. Here, we report a voltage-free pyro-electrification (PE) process able to induce a permanent dipole orientation into polymer sheets under both mono- and bipolar distribution. The technique makes use of the pyroelectric effect for generating electric potentials on the order of kilovolts by an easy-to-accomplish thermal treatment of ferroelectric lithium niobate (LN) crystals. The PE allows us to avoid the expensive and time-consuming fabrication of high-power electrical circuits, as occurs in traditional generator-based techniques. Since the technique is fully compatible with spin-coating-based procedures, the pyro-electrified polymer sheets are easily peeled off the surface of the LN crystal after PE completion, thus providing highly stable and freestanding charged sheets. We show the reliability of the technique for different polymers and for different applications ranging from live cell patterning to biofilm formation tests for bacteria linked to food-processing environments.

Bridging the Gap: Rewritable Electronics Using Real-Time Light-Induced Dielectrophoresis on Lithium Niobate

In the context of micro-electronics, the real-time manipulation and placement of components using optics alone promises a route towards increasingly dynamic systems, where the geometry and function of the device is not fixed at the point of fabrication. Here, we demonstrate physically reconfigurable circuitry through light-induced dielectrophoresis on lithium niobate. Using virtual electrodes, patterned by light, to trap, move, and chain individual micro-solder-beads in real-time via dielectrophoresis, we demonstrate rewritable electrical contacts which can make electrical connections between surface-bound components. The completed micro-solder-bead bridges were found to have relatively low resistances that were not solely dominated by the number of interfaces, or the number of discrete beads, in the connection. Significantly, these connections are formed without any melting/fusing of the beads, a key feature of this technique that enables reconfigurability. Requiring only a low-power (~3.5 mW) laser source to activate, and without the need for external power supply or signal generation, the all-optical simplicity of virtual-electrodes may prove significant for the future development of reconfigurable electronic systems.

Electrical anisotropy and multidimensional pressure sensor of aligned Fe3O4@silver nanowire/polyaniline composite films under an extremely low magnetic field

The PDMS sealed aligned Ag nanowire/PANI composite film as a multi-dimensional pressure sensor.

Bipolar Patterning of Polymer Membranes by Pyroelectrification

Polymer freestanding membranes with permanent bipolar patterns are fabricated by "pyroelectrification". The thermal stimulation of periodically poled lithium niobate (PPLN) crystals simultaneously generates the pyroelectric effect, the glass transition of the polymer, and therefore the periodic electric poling of the polymer. The reliability of these membranes is demonstrated for applications under both dry and wet conditions, including cell patterning.

From bipolar to quadrupolar electrode structures: an application of bond-detach lithography for dielectrophoretic particle assembly

We describe a new, simple process for fabricating transparent quadrupolar electrode arrays enabling large-scale particle assembly by means of dielectrophoresis. In the first step, interdigitated electrode arrays are made by chemical wet etching of indium tin oxide (ITO). Then, the transition from a bipolar to a quadrupolar electrode arrangement is obtained by covering the electrode surface with a thin poly(dimethylsiloxane) (PDMS) film acting as an electrical insulation layer in which selective openings are formed using bond-detach lithography. The PDMS insulating layer thickness was optimized and controlled by adjusting experimental parameters such as the PDMS viscosity (modulated by the addition of heptane) and the PDMS spin-coating velocity. The insulating character of the PDMS membrane was successfully demonstrated by performing a dielectrophoretic assembly of polystyrene particles using interdigitated electrodes with and without a PDMS layer. The results show that the patterned PDMS film functions properly as an electrical insulation layer and allows the reconfiguration of the electric field cartography. Electric field simulations were performed in both configurations to predict the dielectrophoretic behavior of the particles. The simulation results are in perfect agreement with experiments, in which we demonstrated the formation of concentrated clusters of polystyrene particles and living cells of regular size and shape.