Free field gradient

Intermolecular quadrupolar 2 Fluctuation of the electric field gradient, moving multipoles Common for />1 In free Ions In solution [la... 

A clear distinction between electrophoresis (field acdion on an object carrying excess free charges) and dielectrophoresis (field gradient acdion on neutral objects) must be borne in mind at all times. 

Fig. 3.4.1 Schematic description of the three-dimensional SPI technique. Gz, Cx and Gy are the phase encode magnetic field gradients and are amplitude cycled to locate each /(-space point. A single data point is acquired at a fixed encoding time tp after the rf excitation pulse from the free induction decay (FID). TR is the time between excitation (rf) pulses. Notice that the phase encode magnetic field gradients are turned on for the duration of the /(-space point acquisition.

Water self-diffusion coefficients (Dh o) have been determined by pulse field gradient NMR for Nation (Nil/) , BPSH, and SPEEKK and have been shown to increase with increasing acid and water content. At high water contents, the values for PEMs approach the corresponding value for pure water. This is due to the increase in volume fraction of free water. At low water content, however. Nation exhibits greater Dnp values than either BPSH or SPEEKK. In corranon with the observations for EOD, this has been attributed to the smaller channels in aromatic-based polymers, leading to a considerably lower dielectric constant for the water in the channels. 

There is a modest increase in the electrical conductance with an increase in the electric-field gradient, an effect that operates with both strong and weak electrolytes (the first Wien effect). More important in the present context is the marked increase in electrical conductance of weak electrolytes when a high-intensity electric field is applied (second Wien effect). The high field promotes an increase in the concentration of ion pairs and free ions in the equilibrium... 

Perhaps not so very well suitable Thus, semiconductor electrodes exhibit limiting currents that arise from the transport of the charge carrier inside the semiconductor. In practice, this means that it is difficult to get current densities above -1 mA cm-2 at moderately doped semiconductors. No such limitation occurs with metals that have roughly l electron per atom free to move under an electron field gradient. The limiting currents that arise with metals are due to the limitation in supply of materials in the solution. 

The diffusion of small molecules in rubbers is of both theoretical and practical importance. The theories of diffusion based on consideration of free volume can be tested by measurement of self-diffusion using methods such as pulsed field gradient NMR. Selfdiffusion of small molecules must be understood for applications of rubbers as seals in contact with solvents, and for example for diffusion of plasticisers and other small molecules. 

---