Ionic Soft Condensed Matters by Molecular
We frequently encounter soft condensed matters, which appear as daily products
(gelatin, paint, etc.) and the constituents of living objects including
proteins and the DNA. The soft condensed matters represent polymers and colloidal solutions.
Here we introduce our recent studies of "ionic soft condensed matters,
the characters (structures and functions) of which are highly influenced by
strong electrostatic forces.
In these ionic materials, the net electrostatic energy that brings forth
structure xceeds thermal energy that tends to destroy the structure about
several times at room temperature. Interestingly, even if the material
is electrically neutral, the attraction force overcomes the repulsive force
since the positive and negative ions recognize each other and have the
tendency of forming ion pairs.
Figure: A charge inverted macroion, (a) All ions, (b) the blowup of the
vicinity of the macroion are displayed. The macroion is a large red sphere,
counterions and coions are light and dark blue spheres, respectively -
Euro.Phys.J., E., p. 371-379 (2002).
The ionic soft condensed matters belong to "strongly coupled Coulomb
system". However, because of the electrostatic energy dominance over
thermal energy by only several times, the softness (or stiffness) of these
materials can be controlled by environmental conditions such as the amount
of salt (ionic strength), pH (concentration of hydrogen ions). We can make
good use of these properties in applications to daily products. It might
be the case with biochemical processes including DNA and proteins to enable
flexible structure changes for storage and reproduction of themselves at
the room temperature.
With this regard, the ionic soft condensed matters are very attractive
and have wide range of physical and chemical applications. For example,
the charge inversion phenomenon, described in the next section,
is expected to be used in gene therapy for delivery of negatively
charged DNA to living cells having negative electrostatic potentials.
1.Charge Inversion of a Macroion in Solvent
2.Electrolyte (Charged) Polymers - Polyampholyte
3.DNA in Nanopore
4.Microwave Heating of Water and Ice
Movie: Molecular Dynamics Simulation of Charge Inversion
Research Purpose and Results