Colloid conductivity

Fig. 2. Schematic representation of a colloidal conducting polymer particle.

The most familiar type of electrokinetic experiment consists of setting up a potential gradient in a solution containing charged particles and determining their rate of motion. If the particles are small molecular ions, the phenomenon is called ionic conductance, if they are larger units, such as protein molecules, or colloidal particles, it is called electrophoresis. 

There are a number of complications in the experimental measurement of the electrophoretic mobility of colloidal particles and its interpretation see Section V-6F. TTie experiment itself may involve a moving boundary type of apparatus, direct microscopic observation of the velocity of a particle in an applied field (the zeta-meter), or measurement of the conductivity of a colloidal suspension. 

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

Lead azide is not readily dead-pressed, ie, pressed to a point where it can no longer be initiated. However, this condition is somewhat dependent on the output of the mixture used to ignite the lead azide and the degree of confinement of the system. Because lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mix for use in low energy electric detonators. A number of different types of lead azide have been prepared to improve its handling characteristics and performance and to decrease sensitivity. In addition to the dextrinated lead azide commonly used in the United States, service lead azide, which contains a minimum of 97% lead azide and no protective colloid, is used in the United Kingdom. Other varieties include colloidal lead azide (3—4 pm), poly(vinyl alcohol)-coated lead azide, and British RE) 1333 and RE) 1343 lead azide which is precipitated in the presence of carboxymethyl cellulose (88—92). 

Conducting Polymer Blends, Composites, and Colloids. Incorporation of conducting polymers into multicomponent systems allows the preparation of materials that are electroactive and also possess specific properties contributed by the other components. Dispersion of a conducting polymer into an insulating matrix can be accompHshed as either a miscible or phase-separated blend, a heterogeneous composite, or a coUoidaHy dispersed latex. When the conductor is present in sufftcientiy high composition, electron transport is possible. 

FIG. 22-44 E mpirical relationship between 2), the volumetric fraction of hq-iiid in common polydisperse foam, and K, the electrical conductivity of the foam divided hy the electrical conductivity of the liquid. [Chang and Lemhch, J. Colloid Interface Sci., 73, 224 (1980).]... 

The reduction of K2TaF7 can also be performed using sodium vapors [584]. This process is conducted at an Na pressure as low as 0.1 torr, which enables the removal of interferring gases such as N, O and H20. The interaction begins at 350°C. The temperature further increases up to 800°C to prevent the condensation of sodium and the formation of colloidal tantalum powder. The product of the interaction is removed from the reactor after cooling and treated with boiled HC1 and HF solutions. The method enables the production of coarse grain tantalum powder with 99.5% purity. 

Where-high purity MU is provided for higher pressure WT boiler plant FW, some form of continuous analyzers for measuring treated water pH and conductivity are almost always installed, as are sodium (Na) ion-selective electrodes for detection of sodium leakage. Automatic online silica analyzers also may be installed, but they measure only reactive (ionizable) silica (Si02), not colloidal or total silica, so caution is required where unforeseen silica leakage may present a problem. 

A DEA is basically a compliant capacitor where an incompressible, yet highly deformable, dielectric elastomeric material is sandwiched between two complaint electrodes. The electrodes are designed to be able to comply with the deformations of the elastomer and are generally made of a conducting material such as a colloidal carbon in a polymer binder, graphite spray, thickened electrolyte solution, etc. Dielectric elastomer films can be fabricated by conventional... 

Ohshima, H Healy, T White, LR, Approximate Analytic Expressions for the Electrophoretic Mobility of Spherical Colloidal Particles and the Conductivity of their Dilute Suspensions, Journal of the Chemical Society, Faraday Transactions 79, 1613, 1983. 

Stigter, D, Kinetic Charge of Colloidal Electrolytes from Conductance and Electrophoresis. Detergent Micelles, Poly(methacrylates), and DNA in Univalent Salt Solutions, Journal of Physical Chemistry 83, 1670, 1979. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Marsh grapefhiit (MGF) pulp was homogenized in 5 volumes of extraction buffer at 4 C and maintained at pH 8.0 (28). The homogenate was stirred for one hour, centrifuged and the supernatant used as the PE extract. Activity was measured by titration with a Brinkman (Westbury, NY) pH stat titrator at pH 7.5 and 30°C in 25 mL of 1 % high methoxyl pectin (Citrus Colloids Limited, Hereford, UK) with O.IM NaCl. PE units are expressed as the microequivalents of ester hydrolysed per minute. Uronic acid analyses were conducted based on the m-phenyl phenol (4) as modified for microplate reading (30). 

Activation studies were conducted at pH 7.5 at 30°C in 20 mL of 0.5% high methoxyl citrus pectin (Citrus Colloids, Hereford, U.K.). Final cation concentration in PE extracts used for activation studies was less than 2 mM as measured by potentiometry. Controls were conducted to correct for non-enzymic alkali consumption, with no polyamine/no PE and polyamine added/no PE. PE activity was normalized as a percentage of activity with no cation addition. 

The role of reversed micelles in the manufacture of fine chemicals with enzymes also needs to be assessed and analysed. An outstanding example is lipase catalysed interesterification to produce cocoa butter substitute from readily available cheap materials (Luisi, 1985). This example of reversed micelles is sometimes referred to as a colloidal solution of water in organic systems. A number of water insoluble alkaloids, prostanoids, and steroids have been subjected to useful transformations (Martinek et al., 1987). Peptide synthesis has also been conducted. The advantages of two liquid phases are retained to a very great extent the amount of water can be manipulated to gain advantages from an equilibrium viewpoint. 

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