Ionic Soft Condensed Matters by Molecular
          Dynamics Simulation

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.

Electrophoresis of a charge inverted macroion

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

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