The 
Interact POP makes particles attract or repel each other according to their charge (opposites charges attract and like charges repel), like subatomic particles.
How to make particles attract or repel each other
Create a particle system.
For information on how to create a particle system see the
Emit Particles help.
Use the tab menu to create a
Property node, and set the Charge attribute of the particles on the Misc tab using an expression.
Note
You can also use the Interact POP’s override charge option on the Defaults tab to set the charge for each particle directly in the Interact POP.
Use the tab menu to create an
Interact node and connect the particle stream to it.
See the Interact node help for specific parameter details.
Tip
To visualize the charges on each particle, insert a 
Color node. In the color node’s parameters, click Parm and set the color components to -$CHARGE, 0, $CHARGE. This will color the positively charged particles blue and the negatively charged particles red.