Molecules in which a water-insoluble hydrophobic group and a water-soluble hydrophilic group are directly linked
by a single chemical bond are called "surfactants (surface-active molecules)."
When the concentration of surfactant molecules in an aqueous solution is increased, the molecules associate with
each other to form self-organized aggregates called "micelles." At this time, the molecules exhibit different
physical properties than when they exist alone. This self-organizing ability is utilized in a variety of products,
such as cleaning agents in the home, and emulsifiers, dispersants, and foaming and defoaming agents in the industry.
As mentioned above, surfactant molecules are often thought of as "detergents," but it is known that an aqueous
solution containing surfactant molecules exhibits viscoelasticity and reduces the flow resistance inside pipes.
Surfactant molecules that exhibit this property are called "flow resistance reducers." In an experiment using
circulating cooling water in a high-rise building, the introduction of a flow resistance reducing agent reduced
the power of the circulation pump to the extent that power consumption was reduced by about 65% in winter and
about 47% in summer compared to before the agent was introduced, and this has attracted attention as a key
substance for achieving energy conservation in order to realize a "low-carbon society." The formation of "string-like
micelles" made by surfactant molecules (molecular groups) is closely related to the expression of viscoelasticity in
this aqueous solution, and by synthesizing new surfactant molecules that combine various hydrophobic and hydrophilic
groups and investigating the physical properties of their aqueous solutions, we are working to clarify the correlation
between the properties of aqueous solutions and the drag reduction effect at the molecular level.
Surfactant molecules can also be used for oil instead of water. It is known that an oil solution in which surfactant
molecules are dissolved loses its fluidity and gels. Surfactant molecules that exhibit this property are called "oil
gelling agents." A familiar example of an oil gelling agent is tempura*, which solidifies tempura oil. The raw
material is castor oil extracted from Chinese sesame seeds (castor bean), and its components are unsaturated fatty
acids and a small amount of saturated fatty acid glycerides. When the temple is dissolved in hot oil, a cage-like
three-dimensional structure appears that traps the oil during the cooling process, and the oil is absorbed into this
structure and solidifies. It is expected to be applied to cosmetics, medicines, and food. This oil gelation is
closely related to the formation of "inverted string-like micelles" made by surfactant molecules (molecular groups).
As with "flow drag reducers," we are working to clarify the gelation mechanism at the molecular level by synthesizing
new surfactant molecules that combine various hydrophobic and hydrophilic groups and investigating their gel properties.
* https://scjcatalog.johnson.co.jp/products/brand/tempuru.html
Related report (Japanese)
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