Ionic conductivity gelation

Dielectric measurements are insensitive to gelation. This important point is mainly based on experiments with epoxy-amine reactions for which the dielectric parameters are controlled by ionic conductivity. More experiments with other chemistries are needed to reach a more universal conclusion. 

Measurements of dielectric properties have been used to monitor chemical reactions in organic materials for more than fifty years. In 1934, Kienle and Race 11 reported the use of dielectric measurements to study polyesterification reactions. Remarkably, many of the major issues that are the subject of this review were identified in that early paper the fact that ionic conductivity often dominates the observed dielectric properties the equivalence between the conductivity measured with both DC and AC methods the correlation between viscosity and conductivity early in cure the fact that conductivity does not show an abrupt change at gelation the possible contribution of orientable dipoles and sample heterogeneities to measured dielectric properties and the importance of electrode polarization at low frequencies. 

To study the mobility of Li" " on the gel matrix, we measured the Li diffusion coefficient before and after gelation of the 2-Li (with 5 wt% PAMPSLi) using pfg-NMR. The Li diffusion coefficient in the gel was almost unchanged from the value before gelation, despite the decrease in the ionic conductivity with gelation. Because, as this result suggests, the mobility of Li is not suppressed by gelation, this gel system is favorable for Li" " conductive materials. 

There are differing opinions on whether gelation can be measured by dielectric analysis. Ionic conductivity is related to viscosity, in that conductivity decreases with increasing... 

Relationship between ionic Conductivity and Gelation Time (tge,) Molecular gelation takes place at a well-defined and generally calculable step in the course of the chemical reaction (Flory 1988). The reaction mechanism is assumed to be temperature-independent and free of noncross-linking side reactions but depends on stoichiometry, reactivity, and functionality of the reactants. Several attempts have been made to relate dielectric results and the gel point [e.g., see Fournier et al. (1996)]. An inflection point... 

Figure 26.4 Dependence of ionic iiquid gei conductivity on concentration of gelator 1 at room temperature (A)C4mim/TFSi, (W) C4mim/BF4, (9) C4mim/PFe, (A) T, (Q) C4Py/BF4, ( ) Cemim/BF4, (x) B, and (U) CePy/PFe-...

For stereoregular charged polysaccharides, the formation of a helical conformation and eventually gelation depend on the ionic concentration, the nature of electrolyte and the temperature. The conformation results from a balance between H-bonds (which stabilize the helical conformation, but which are destabilized when the tenpera-ture increases) and electrostatic repulsions between the charges on the polymer (which are screened by external salt addition). The helix-coil transition for K-carrageenan was demonstrated by different techniques, viz. conductivity. 

Shibata Y., Kato T., Kado T., Shiratuchi R., Takashima W. Kaneto K. (2003). Quasi-solid dye sensitized solar cells filled with ionic liquid-increase in efficiencies by specific interaction between conductive polymers and gelators, Chem. Commun., n°21, pp. 2730-2731 (November 2003), ISSN 1359-7345... 

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