Electrical birefringence conductivity

Fig. 4a,b Specific electric birefringence measured at E=2105 V/m (top) and conductivity contribution of the polyelectrolyte Ak (bottom) versus concentration of added salt, squares NaCl triangles up NaI triangles down N(C2H5)4I circles Na2S04. All data have been taken from ref. [49]... 

The behavior of water in oil microemulsions has been studied using different techniques light scattering, electrical conductivity, viscosity, transient electrical birefringence, ultrasonic absorption. All these experiments lead us to propose a picture of the microemulsions structure which assignes an important role to the fluidity of the interfacial region. 

Shrmomura, T. et ah. Intrachain conduction and main-chain conformation of conducting polymers as studied by frequency-domain electric birefringence spectroscopy, Phys. Rev. Lett. 72, 2073-2076, 1994. 

Shrmomura, T. et al.. Frequency-domain electric birefringence spectra of conducting polymers, Synth. Met. 69, 689-690, 1995. 

There is a good correlation between the strength of the attractive interactions and the amplitude of the electrical birefringence signals as well as the electrical conductivity variation around the percolation threshold [23]. This is because when attractive interactions are present, the formation of droplet aggregates is favored. These aggregates are anisotopic and are easily oriented by an electric field. They also promote percolation at lower volume fractions than for a hard sphere. This is discussed in more detail in Sec. II. B. 

According to these requirements, clearly, ternary W/O microemulsions of a nonionic surfactant are ideal systems to be studied by transient electrical birefringence. The requirement is fulfilled to a progressively lesser degree as the microemulsion s conductance increases in the order O/W microemulsions of nonionic surfactants < W/O ionic <0/W ionic. 

We have also demonstrated that it was possible to throw light on the orientation fluctuations of polar macromolecules like collagen, by measuring the noise emission conductivity (t versus frequency. The critical time of orientation fluctuations of the collagen permanent dipoles cannot be assimilated to the classical dielectric relaxation time T , but the numerical value of is very near to the reorientation time measured by electrical birefringence. 

Before giving analytical expressions for the director deformations in Freedericksz cells, we will summarize the magnetic and electrical methods. The advantage of electro-optical measurements is that the cell thickness does not enter the equations and is therefore ruled out as an error source. Furthermore, the electric field can always be considered strictly perpendicular to the sample plane. On the other hand, in the electric method conductivity effects can influence the measurements and exact knowledge of and is required to extract the second elastic constant from the birefringence or capacitance characteristics. Moreover, the electric measurement is restricted... 

There are two kinds of electric birefringence techniques, the FEBS and the transient electric birefringence (TEB) method [171, 173]. The TEB method was applied to the solution of polydiacetylene to investigate the rod-coil conformational transition of the polymer chains [174]. The FEBS, on the other hand, has the advantage of giving us the mobility of the carriers along the polymer chain separately from the hydrodynamic radius of the polymer chain (usually referred to as the polymer conformation) [149]. Shimomura et al. [175] have recently applied the FEBS technique to the solutions of dilutely doped PHT to study the intrachain conduction in the conducting polymer and its relation to the main-chain conformation. 

The electrical conductance shows a weaker concentration dependence above than below the CMC corresponding to a decrease in the equivalent conductance (Fig. 2.10). The transport number of the surfactant ion rises sharply at the CMC while that of the counterion may become negative. This as well as electrophoretic mobilities may yield information on micellar charge. At high concentrations, conductance anisotropies have been observed for flowing systems. This, as well as flow birefringence, is useful for the demonstration of nonspherical micelle shape. 

In many of these studies the structure of the middle phase is not established, but it is clearly immiscible in water or oil and its electrical conductivity is closer to water than oil. Phase diagram studies of oil-water-emulsifier systems Ekwall, (5), indicate that surfactant-rich phases immiscible in oil or wa"ter have rodshaped or lamellar micelles with some degree of optical anisotropy or flow birefringence, and these phases have much greater elec-rical conductivity than oil. Figure 1 illustrates that the middle phase composition varies smoothly from a water-rich composition to an oil-rich composition as the emulsifier partition changes from mostly water-soluble to mostly oil-soluble. If lamellar structures are present the relative thickness of oleophilic and hydrophilic layers must vary smoothly from the water-rich compositions to the oil-rich compositions. 

To illustrate this point. Figure 15.10 shows the change in electrical resistance (reciprocal of conductivity) with the ratio of water to oil (V /VJ for a microemulsion system prepared using the inversion method [14]. The data in Figure 15.10 indicate the change in optical clarity and birefringence with the ratio of water to oil. 

The most uncommon molecular structure known so far to produce lyotropic mesophases is that of the chiral, dinuclear chromium(II) complex of phenanthroline and tartaric acid, (323). The complex does not possess an amphiphilic structure, i.e., no polar headgroup nor aliphatic tail, does not belong to the columnar type, and does not show thermotropic properties. Thus, the phenanthroline ligands must play the role of the hydrophobic part, while the central tartrate link must act as the hydrophilic one. A room-temperature, lyotropic mesophase was induced at low concentration in water (0.006 mol dm ). Moreover, in the concentration range of 0.06 to 0.1 mol dm the mesophase was still observed and remained stable up to 100 °C. The self-aggregation of the complex into a birefringent mesophase was proved by the use of several techniques including polarized optical microscopy, viscosity, and electrical conductivity measurements, as well as Na... 

According to Raman spectroscopy data, the polymers consist of alternate conjugated double and triple bonds. The shapes of the monomer crystals are not altered on polymerization. The polymer crystals are highly colored and birefringent they also conduct electricity. 

A view on the physical phenomena engendered by sonication would not be complete without a brief mention of less known aspects, such as the acoustic birefringence and the effect on electrical conductivity. Both phenomena are generally ignored by sonochemists. Determining their fundamental significance is in any case premature nevertheless, they should be placed within the general framework of the electrical theories. 

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