Electrolytic expansion measurement

Figure 8.2 Schematic diagrams for the measurement of electrolytic expansion along (a) the film length and (b) the thickness direction. WE, RE and CE are the working electrode, reference electrode and counter electrode, respectively.

Using dilatometry in parallel with cyclic voltammetry (CV) measurements in lmolL 1 LiC104 EC-l,2-dimethoxy-ethane (DME), Besenhard et al. [87] found that over the voltage range of about 0.8-0.3 V (vs. Li/Li+), the HOPG crystal expands by up to 150 percent. Some of this expansion seems to be reversible, as up to 50 percent contraction due to partial deintercalation of solvated lithium cations was observed on the return step of the CV. It was concluded [87] that film formation occurs via chemical reduction of a solvated graphite intercalation compound (GIC) and that the permselective film (SEI) in fact penetrates into the bulk of the HOPG. It is important to repeat the tests conducted by Besenhard et al. [87] in other EC-based electrolytes in order to determine the severity of this phenomenon. 

In order to compare the structural parameters of the foam model studied by Kruglyakov et al. [18] with the respective parameters of a real polydisperse foam (individual bubbles of different degree of polyherdisity) Kachalova et. al. [19] performed measurements of the average border radius of curvature of foams with variable expansion ratio. The foam studied, generated by the set-up shown in Fig. 1.4, was obtained from a nonionic surfactant solution of Triton-X-100 (a commercial product) to which NaCl (0.4 mol dm 3) was added. The expansion ratio was determined conductometrically with correction of the change in electrolyte concentration due to the internal foam destruction. The electrolyte concentration... 

Most macromolecules when dissolved in salt solutions acquire charges that are shielded by an atmosphere of counterions. This ion atmosphere affects the diffusion coefficient of the macromolecule and hence the light-scattering time-correlation function. Electrolyte solutions are discussed in Chapters 9 and 13. Recent measurements of diffusion coefficients have been made by several groups. Lee and Schurr (1974) have studied poly-L-lysine-HBr. Schleich and Yeh (1973) have performed similar studies on poly-L-proline. Raj and Flygare (1974) have studied bovine serum albumin (BSA) and find that at high ionic strength and low pH the diffusion constant decreases. This they attribute to the expansion of the molecule. 

Thus, macroscopic (e.g., viscosity) and molecular-level (e.g., D andA2) measurements are consistent with a model for NVP/SPE copolymers that is intramolecularly associated in water or low-salt solutions. These intramolecular aggregates are both of the intragroup and intrachain type. Such intramolecular aggregates are broken up by external electrolytes (e.g. NaCl), with a consequent modest expansion of the polymer coil (Figure 6). Thus, the solution properties for sulfo zwitterion copolymers with NVP confirm earlier trends reported for sulfo zwitterion homopolymers (3-6). 

The dependence of the measured resistance of the cell electrolyte on oxygen activity in the gas phase. This dependence, which was first revealed by E. Shouler [16], led to the notion "expansion of the three-phase region". However, if we estimate numerically the value of the electron conduction, which would provide the observed change of the measured resistance of the electrolyte, it becomes apparent that the observed dependences cannot be explained in terms of the base model. This expansion of the three-phase region was studied recently using model electrodes and the metal/electrolyte contact geometry was determined well [17-20]. 

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