Water-containing ionically conducting

Transcutaneous Electrical Nerve Stimulation. Water-containing, ionically conductive pol piers are used in transcutaneous electrical nerve stimulator (TENS) treatment to deUv electrical pulses to the underlying n e and muscle tissue to eitho rdieve acute and chronic pain or to repair and regoiorate damaged tissue (2). TENS electrodes typically consist of a nonmetallic conductor, an adhesive t patch, and a conductive gel medium between the skin and the conductor. 

This brief sampling of chemistries illustrates many of the approaches used to encompass the diverse range of performance requirements for this important class of materids. Upon review, the chemistry of water-containing, ionically conductive polymer systems reveals a variety of approaches that can be used to tailor the range of properties to a specific application. The commercial importance of water-containing ionically conductive polymer systems requires the continued development of new chemistries and processes to meet the ever increasing performance demands. 

Water-containing, ionicaUy conductive polymers are uniquely versatile and hold high economic value in industry. The patent Uterature contains a plethora of examples of novel chemistries and uses. Historically ionic conductivity was viewed as an undesirable property, which interfered with the intended insulating properties of polymers. As a consequence, the Uterature suffers from a relative paucity of informative articles or reviews (i). In this paper we review the chemistries, properties, and appUcations of several patentkl and commerciaUy available conductive polymer systems. 

The presence of ions in solution is what gives a sodium chloride solution the ability to conduct electricity. If positively and negatively charged wires are dipped into the solution, the ions in the solution respond to the charges on the wires. Chloride anions move toward the positive wire, and sodium cations move toward the negative wire. This directed movement of ions in solution is a flow of electrical current. Pure water, which has virtually no dissolved ions, does not conduct electricity. Any solution formed by dissolving an ionic solid in water conducts electricity. Ordinary tap water, for example, contains Ionic Impurities that make It an electrical conductor. 

To be ionically conducting, the fluorocarbon ionomer must be wet under equilibrium conditions, it will contain about 20 percent water. The operating temperature of the fuel cell must be... 

In a vessel containing these three substances, there is no tendency to go the other way, from water to form hydrogen and oxygen. This can be made to occur, however, if an electrolyte such as NaOH is put into the water to produce ionic conduction and the conditions of a driven cell (Fig. 7.4) are set up (the two electrodes and the outside power source). 

Postcolumn photochemical reactions are another approach to the detection problem. High-intensity UV light, generally provided by a Hg or Zn lamp, photolyzes the HPLC effluent, which passes through a Teflon (47) or quartz tube. The photolysis reaction determines the nature of the subsequent detection. If the compound has a UV chromophore, such as an aromatic ring, and an ionizable heteroatom, such as chlorine, then the products of the reaction can be detected conductometrically. Busch et al. (48) have examined more than 40 environmental pollutants for applicability to detection with photolysis and conductance detection. Haeberer and Scott (49) found the photoconductivity approach superior to precolumn derivatization for the determination of nitrosoamines in water and waste water. The primary limitation of this detection approach results from the inability to use mobile phases that contain ionic modifiers, that is, buffers and... 

A solute may be present as ions or as molecules. We can identify the form of the solute by noting whether the solution conducts an electric current. Because a current is a flow of electric charge, only solutions that contain ions conduct electricity. There is such a tiny concentration of ions in pure water (about 10-7 m) that water alone does not conduct electricity. A substance that dissolves to give a solution that conducts electricity is called an electrolyte. Electrolyte solutions (solutions of electrolytes), which conduct electricity because they contain ions, include aqueous solutions of ionic compounds, such as sodium chloride and potassium nitrate. The ions are not formed when an ionic solid dissolves they exist as separate ions in the solid but become free to move apart in the presence of water (Fig. 1.1). Acids also are electrolytes. Unlike salts, they are molecular compounds in the pure state but form ions when they dissolve. One example is hydrogen chloride, which exists as gaseous HC1 molecules. In solution, however, HCl is called hydrochloric acid and is present as hydrogen ions and chloride ions. 

Passivity — An active metal is one that undergoes oxidation (-> corrosion) when exposed to electrolyte containing an oxidant such as O2 or H+, common examples being iron, aluminum, and their alloys. The metal becomes passive (i.e., exhibits passivity) if it resists corrosion under conditions in which the bare metal should react significantly. This behavior is due to the formation of an oxide or hydroxide film of limited ionic conductivity (a passive film) that separates the metal from the corrosive environment. Such films often form spontaneously from the metal itself and from components of the environment (e.g., oxygen or water) or may be formed by an anodization process in which the anodic current is supplied by a power supply (see -> passivation). For example, A1 forms a passive oxide film by the reaction... 

Determination of Ionic Product Conductance Method.—Since it contains a certain proportion of hydrogen and hydroxyl ions, even perfectly pure water may be expected to have a definite conductance the purest water hitherto reported was obtained by Kohlrausch and Heyd-weiller after forty-eight distillations under reduced pressure. The specific conductance of this water was found to be 0.043 X 10 ohm cm. at 18 , but it was believed that this still contained some impurity and the conductance of a 1 cm. cube of perfectly pure water was estimated to be 0.0384 X 10 ohm i cm. at 18 . The equivalent conductances of hydrogen and hydroxyl ions at the very small concentrations existing in pure water may be taken as equal to the accepted values at infinite dilution these are 315.2 and 173.8 ohms cm. respectively, at 18 , and hence the total conductance of 1 equiv. of hydrogen and 1 equiv. of hydroxyl ions, at infinite dilution, should be 489.0 ohms cm. It follows, therefore, that 1 cc. of water contains... 

Some substances conduct electricity and some cannot. The conductivity of a substance depends on whether it contains charged particles, and these particles must be able to move. Electrons move freely within a metal, thus allowing it to conduct electricity. Solid NaCl contains ions, but they cannot move, so solid NaCl is a nonconductor by itself But an aqueous solution of ionic compounds such as NaCl contains charged ions, which can move about. Solutions of ionic compounds conduct electricity. Pure water does not conduct electricity. 

If you collect rainwater in a relatively unpolluted area, you will discover that the rainwater is essentially a nonconductor of electricity. A small concentration of carbonic acid from the carbon dioxide in the air added to the rainwater causes the rain water to be a weak conductor. Pure rainwater conducts almost as poorly as distilled water. However, most of the water we use comes from wells, lakes, or rivers. This water has been in contact with soil and rocks, which contain ionic compounds that dissolve in the water. Consequently, tap water conducts electricity. The conduction is not high, but the water can conduct enough current to stop a person s heart. So, for example, a person should not use an electrical appliance when in the bathtub or shower. 

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