NEW SOLID MEDIUM FOR ELECTROCHEMISTRY AND ITS APPLICATION TO DYE-SENSITIZED SOLAR CELLS - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 122

A Solid Medium wherein Molecular Diffusion Takes Place the
Same as in a Liquid but Convection ss Prohibited

Molecular Diffusion and Bulk Convection

In a liquid or gas phase a molecule diffuses both by self-diffusion and convection when
there exists no other disturbing factor such as stirring or flow of the medium. Between the
self-diffusion and convection, convection contributes much more to the transport of
molecules in the whole liquid or gas phase than self-diffusion ( vide infra ). However, it is not
recognized in general how convection is important for a molecule to move throughout the
liquid or gas phase. It is an important and interesting research subject to investigate the degree
of molecular diffusion (movement) by discriminating the self-diffusion and convection.
However, it has been impossible to discriminate self-diffusion and convection since
convection always take place on the earth due to the presence of gravity except the cosmic
space where convection does not occur due to the absence of gravity. Prohibition of
convection is also important for crystal growth for which convection prohibits large and good
crystal growth by disturbing concentration gradient near the growing crystal surface. On this
reason cosmic space has been attracting attention to obtain ideal crystals where convection
does not take place due to the absence of gravity.
It has been shown in the last sections 3 and 4 that, in a polysaccharide solid involving
excess water, molecular diffusion can take place the same as in a liquid water. Various
reactions including photochemical and electrochemical reactions can take place in this solid
the same as in an aqueous solution. In this solid molecules can diffuse freely as in liquid
water, but we have found that bulk convection does not take place because of the macroscopic
solid state of the material [6]. Convection always takes place in a liquid or gas phase on the
earth because of the gravity, and so can be prohibited only in the cosmic space. If convection
can be prohibited on the earth, it would lead to new basic science, chemical reactions, as well
as applications to such as crystal growth. In this section 5 a different aspect of the
polysaccharide solid will be mentioned wherein bulk convection does not take place.

Prohibition of Bulk Convection in Polysaccharide Solids

Three -dimensional self-diffusion of thionine dye ( 3 ) was investigated in an agarose solid
involving excess water.

N

H 2 N NH 2

S

Cl

3 (thionine dye) .