Polymer Composites Containing Non-Covalently Functionalized Carbon Nanotubes: A Study of Their Dispersion Characteristics and Response to AC Electric Fields

AbstractMulti-wall carbon nanotubes (MWCNT) functionalized with a hyperbranched polyethylene (HBPE) and subsequently melt compounded with an ethylene-octene copolymer (EOC8100) matrix are examined in terms of their dispersion characteristics and electric field response. It was found that, when compared with their non-functionalized counterparts, HBPE-functionalized MWCNT produce substantially more uniform composites. On the other hand, MWCNT functionalization results in a higher electrical percolation threshold. Electrification of the composite melts showed that longer insulator-to-conductor transition times should be expected as a consequence of the improved dispersion quality. The functionalization, however, did not prevent MWCNT from forming highly electrically conducting networks in the melt, or exhibiting electric field-induced percolation thresholds of less than 1wt% filler

Electrical Sintering of Silver Nanoparticle Ink Studied by In-Situ TEM Probing

Metallic nanoparticle inks are used for printed electronics, but to reach acceptable conductivity the structures need to be sintered, usually using a furnace. Recently, sintering by direct resistive heating has been demonstrated. For a microscopic understanding of this Joule heating sintering method, we studied the entire process in real time inside a transmission electron microscope equipped with a movable electrical probe. We found an onset of Joule heating induced sintering and coalescence of nanoparticles at power levels of 0.1–10 mW/m3. In addition, a carbonization of the organic shells that stabilize the nanoparticles were found, with a conductivity of 4 105 Sm−1

Contact-Free Templating of 3‑D Colloidal Structures Using Spatially Nonuniform AC Electric Fields

The formation of ordered and regularly shaped structures of colloidal particles with the aid of spatially nonuniform electric fields is a modern research area of great interest. This work illustrates how alternating current (AC) electrokinetic effects (dielectrophoresis, electroosmosis) can serve as contact-free templates, inside which colloidal microspheres can assemble into a variety of shapes and sizes. We show how three-dimensional colloidal structures of square, circular, and diamond shape of many tens of micrometers in size can be reproducibly formed with a single set of quadrupolar microelectrodes. Numerical simulations performed help to explain the role of AC electroosmosis and AC dielectrophoresis on the shaping of these structures as a function of applied voltage and frequency. We also demonstrate how the templating <i>repertoire</i> is further enhanced with the simultaneous application of a second, individually controlled AC electric field, which enables a variety of asymmetric colloidal structures to be produced using the same set of quadrupolar microelectrodes. As the preservation of shape and size of such electric-field templated structures after medium evaporation still remains a big challenge, here we also report on a novel method that permits the stabilization and isolation of these particle assemblies through medium gelation and subsequent hydrogel removal with a UV/ozone treatment

Dielectrophoretic forces can be safely used to retain viable cells in perfusion cultures of animal cells.

Δημοσίευση σε επιστημονικό περιοδικόSummarization: Dielectrophoresis is a well established and effective means for the manipulation of viable cells. However, its effectiveness greatly depends upon the utilization of very low electrical conductivity media. High conductivity media, as in the case of cell culture media, result only in the induction of weaker repulsive forces (negative dielectrophoresis) and excessive medium heating. A dielectrophoresis-based cell separation device (DEP-filter) has been recently developed for perfusion cultures that successfully overcomes these obstacles and provides a very high degree of viable cell separation while most of the nonviable cells are removed from the bioreactor by the effluent stream. The latter results in high viabilities throughout the culture period and minimization of lysed cell proteases in the bioreactor. However, an important question that remains to be answered is whether we have any adverse effects by exposing the cultured cells to high frequency electric fields for extended periods of time. A special chamber was constructed to quantitate the effect under several operational conditions. Cell growth, glucose uptake, lactate and monoclonal antibody production data suggest that there is no appreciable effect and hence, operation over long periods of time of the DEP-filter should not have any adverse effect on the cultured cells.Presented on: Cytotechnolog