NEW SOLID MEDIUM FOR ELECTROCHEMISTRY AND ITS APPLICATION TO DYE-SENSITIZED SOLAR CELLS - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 120

Although the ionic conductivity changes much with the polysaccharide concentration
(later shown in figure 12), the double-layer capacitance values estimated from impedance
spectra (table 3) are almost independent of the polysaccharide concentration.
We examined the ionic conductivity changes of figure 11 in more detail. The agarose
concentration dependence of the hardness and the conductivity of the solids containing 0.1 M
KCl are obtained from figure 11 and shown in figure 12.
Figure 12. Concentration dependence of the conductivity of agarose solids containing 0.1 M KCl
aqueous solution and the hardness of the solids as a function of the agarose concentration [5].
For the 1 and 2 wt% agarose solids, they are so soft that the hardness was not able to be
measured with the present hardness meter. For the 3-5 wt% agarose concentrations, they form a
tight and elastic solid. The conductivity decreased with the increase in the agarose concentration
from 1 to 3 wt%. On the other hand, the conductivity increased with the increase in the agarose
concentration from 3 to 5 wt%. That is, the conductivity decreased with the polysaccharide
concentration while the solid is very soft, but the conductivity increased with the increase in the
hardness when it forms a tight solid. When a polysaccharide becomes a solid including excess
water, three dimensional network is formed by single or double helical structure. Now, when
the agarose concentration is low (< 3 wt%), it is considered that the three dimensional network
structure would not grow up enough. In this range, the network structure is sparse and the
chains must be very flexible, so that a steric hindrance by agarose chains in the liquid phase
would increase with the increase in the agarose concentration; it is inferred that the diffusion of
dissolved ions is prohibited by the agarose chains in this case. However, above the 3 wt%
agarose concentrations, the growth of three dimensional networks increase remarkably with the
increase in the agarose concentration. In this case, the flexibility of the chains must be lowered
by the addition of polysaccharide, so that it is inferred that the further addition of agarose would
not block the ionic diffusion in liquid phase, but rather enhances ionic diffusion by forming
more rigid network.