Short Answer: At the current time, there is not enough dark energy in the universe to affect the distance between the particles. This may not always be the case though...
An interesting paper was submitted in 2003 by <PERSON> of Dartmouth College and his team, on the Big Rip theory.
A universe dominated by phantom energy is an accelerating universe, expanding at an ever-increasing rate. However, this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point moves ever closer. When the size of the observable universe becomes smaller than any particular structure, no interaction by any of the fundamental forces can occur between the most remote parts of the structure. When these interactions become impossible, the structure is "ripped apart". The model implies that after a finite time there will be a final singularity, called the "Big Rip", in which all distances diverge to infinite values.
In their paper, the authors consider a hypothetical example with w = −1.5, H0 (Hubble's Constant) = 70 km/s/Mpc, and Ωm (density of matter in the universe) = 0.3
Using these figures in their calculations they estimate that in 21.94B years from now, the force of gravity will cease holding the galaxies together.
59.1 years later solar systems would cease to be held together by gravity.
Then perhaps days or hours before the big rip, planets and matter would break down and finally at the big rip, subatomic particles would be ripped apart.
There is debate about what the value of w is. Evidence indicates w to be very close to −1 in our universe, which makes w the dominating term in the equation. The closer that w is to −1, the closer the denominator is to zero and the further the Big Rip is in the future. 150
If w were exactly equal to −1, the Big Rip could not happen, regardless of the values of H0 or Ωm.
According to the latest cosmological data available, the uncertainties are still too large to discriminate among the three cases w < −1, w = −1, and w > −1. ("WMAP 9 Year Mission Results". wmap.gsfc.nasa.gov.) & (<PERSON>, S. W.; <PERSON>, <PERSON>; <PERSON>, <PERSON>; <PERSON>, H.; <PERSON>, <PERSON>; <PERSON>, A. C. (2008). "Improved constraints on dark energy from Chandra X-ray observations of the largest relaxed galaxy clusters". Monthly Notices of the Royal Astronomical Society.)
If the paper holds out as true, then the universe will only last another 22B years or so... We will have to wait to see. 419