What physical interactions actually make single stars leave their binary companions at formation? From an interesting ScienceDaily article, I read this

Before the groups of stars disperse, binary stars move through their
  birth sites and the group studied how they interact with other stars
  gravitationally. "In many cases the pairs are torn apart into two
  single stars, in the same way that a pair of dancers might be
  separated after colliding with another couple on a crowded dance
  floor," explains Michael Marks, a PhD student and member of the
  International Max-Planck Research School for Astronomy and
  Astrophysics. The population of binaries is therefore diminished
  before the stars spread out into the wider Galaxy.
The stellar nurseries do not all look the same and are crowded to
  different extents, something described by the density of the group.
  The more binaries form within the same space (higher density groups),
  the more interaction will take place between them and the more binary
  systems will be split up into single stars. This means that every
  group has a different composition of single and binary stars when the
  group disperses, depending on the initial density of stars.

Here's the question: what are the types of gravitational interactions that make binary systems split up into single stars?
 A: 2-body situations alone (pairs of stars) cannot eject anything, usually. What happens a lot is that a close binary is visited by another star, or by another close binary. The outcome is hard to visualize, but sometimes it ejects one star from the group at high velocity. It could eject one of the binary components, or the visitor - all bets are off.
I used to do simulations like that, way before, and I was always amazed by the speedy rogues that were ejected from populous groups. You could do that yourself with the Universe Sandbox:
http://universesandbox.com/
If you can't setup a binary + singlet collision, just select the galaxy collision and watch the rogues spewed out.
A: It is just one interaction - gravity:
As you mention in your comment, it is exactly analogous to the situation where a spaceprobe gets accelerated by Jupiter's gravity. 
In a cluster of stars, any time a pair of stars comes close to another pair or more (close here just means close enough for one of the pair to be affected more than the other) the difference in forces can accelerate them in very different directions.
