Direct currents , polymer electricity

Supramolecular assemblies including CNTs have proven difficult due to challenges associated with dispersing SWNTs in neat solvents and to the difficulty in controlling molecular orientation. In one example of supramolecular assembly, a direct current (DC) electric field was employed to induce surfactant (tetraoctlyammonium bromide) or polymer (Nafion) capped SWNTs to assemble into linear bundles. On the basis of the knowledge that fullerenes can experience charge-transfer interactions with porphyrins to form supramolecular assemblies, Kamat and coworkers determined that protonated porphyrins yielded ordered... 

Figure 1.1 A solution of polymer (e.g., collodion or cellulose nitrate in ether or acetone) delivered into the high-voltage direct current (DC) electric field via tube B to form electrospun nanofibers collected on a drum F. (Source Cooley 1902, Fig. 5 of U.S. patent 692, 631.)...

Of greater interest in recent years have been the peculiar piezolectric properties"" of polyfvinylidene fluoride). In 1969 it was observed" that stretched film of the polymer heated to 90°C and subsequently cooled to room temperature in a direct current electric field was 3-5 times more piezoelectric than crystalline quartz. It was observed that the piezolectric strain coefficients were higher in the drawn film and in the normal directions than in the direction transverse to the film drawing. 

The ion movement can be controlled by ion exchange or ion transfer membranes, thin sheets of cross-linked organic polymers with ion exchange properties—for example, sulfonated polystyrene-divinylbenzene polymers. Both cation-permeable and anion-permeable membranes are available and have been described (3, 9). To achieve demineralization, these membranes are spaced alternately between a cathode and an anode which introduce direct current. The compartment between each pair of membranes is filled with a saline water. The resulting ion motion is controlled by the membranes, so that one set of compartments—for example, the even-numbered compartments—lose ions and the odd-numbered compartments gain ions. The product from the ion-losing cells is collected and comprises electrically demineralized water. 

Electrical Measurements. The electrical properties of polymers have much in common with mechanical properties. They can be divided into static properties equivalent to direct current properties and dynamic properties resulting from alternating current measurements. The most used parameter is the volume or bulk resistivity (ASTM-D257-75b) which is the resistance in ohms of a material 1 cm thick and 1 cm2 area. Bulk resistivity is one of only a few properties that vary nearly 1025 in typical use (materials with values above 10 ohm-cm for polystyrene to 10 5 ohm-cm for copper). 

Hydrogen-powered cars are based on fuel cells that store hydrogen, or H2 gas, inside a material called a polymer exchange membrane. The fuel cell contains two electrodes an anode (negative side) and a cathode (positive side). At the anode, the H2 molecules are split into protons and electrons. The protons pass through a polymer exchange membrane, while the electrons are unable to pass through this membrane and thus have to flow in a different direction. This creates a current of electricity by which the car is powered. 

A number of creative ways have been developed to create nonuniformities in an electric field using insulators. Initial efforts simply used prefabricated posts embedded in the channels [6] or rectangular [8], triangular [3], oil menisci [9], and other protrusions into the channels. The most common insulator materials are polymers utilized for photolithography or hot press microfahrication including polydimethylsiloxane PDMS and polymethyl methacrylate PMMA, or glass or silicone, which can be chemically etched or ablated [2]. A key attribute of direct current dielectrophoresis is that the electrodes supplying the electric field can be located more remotely on the lab-on-a-chip device. Electrodes can be immersed in fluid in chambers at either end of the test channel to avoid detrimental electrolysis reaction products [31]. Please see Pig. 1. 

In EA experiments, the electric field in the polymer layer, arising fi-om the application of a sinusoidal voltage of the form V = V dc + cos(wt), consists of the superposition of a direct current (DC) component (Fq) and an alternating current (AC) component (Fac) ... 

Volume resistivity (specific insulation resistance) n. The ratio of the potential gradient parallel to the current in a material to the current density. In SI, volume resistivity is numerically equal to the direct current resistance between opposite faces of a one-meter cube of the material, with the unit ohm-meter (Qm). The smaller cgs unit, Q cm, is still widely used. Giambattista A, Richardson R, Richardson RC, Richardson B (2003) College physics. McGraw Hill Science, New York. Ku CC, Liepins R (1987) Electrical properties of polymers. Hanser Publishers, New York. 

Converting tidal energy current to electrical current poses a major polymer composite materials challenge. The hydrosphere is seen to be a particularly hostile environment when one realises that water is some 830 times denser than air the exact value will depend upon its depth. The flow is varying and often turbulent and will reverse in direction with the ebb and flow of the tide. Moisture ingress is a constant hazard exacerbated by device motion and equipment maintenance the latter event has to take place infrequently as generally the access to submerged installations is limited. Furthermore,... 

Kilbride B E, Coleman J N, Fraysse J, Fournet P, Cadek M, Drury A, Hutzler S, Roth S and Blau W J (2002) Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films, J Appl Phys 92 4024-4030. Sandler J K W, Kirk J E, Kinloch I A, Shaffer MSP and Windle A H (2003) Ultra-low electrical percolation threshold in carbon-nanotube-epoxy composites. Polymer 44 5893-5899. 

Electrophoretic Deposition n A direct-current process analogous to electroplating, used to coat electrically-conductive articles with plastics, deposited from aqueous lattices or dispersions. The cathode may be a noncorrodible metal such as stainless steel, generally serving as the container in which the process is performed. The DC potential is usually under 100 V. The deposited coatings are baked to remove residual water. Among available polymer lattices suitable for the process are PVC, polyvinylidene chloride, acrylics, nylons, polyesters, polytetrafluoroethylene, and polyethylene. 

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