In SOLiD sequencing, the beads used for emulsion PCR are covalently coupled with many copies of  a primer sequence.  The DNA fragments to be sequenced are first ligated to an oligo that is complementary to the bead primer.  When the ligated fragments and beads are mixed, the fragments bind via the complementary sequences and the fragment can be replicated from the bead-bound primer.  In the emulsion PCR process, the goal is for one bead and one fragment to occur together in one aqueous "bubble' and for many copies of the fragment to be amplified while attached to the bead.  The emulsion is just a mix of oil and aqueous solution, so it can be easily broken by the addition of an organic solvent, like butanol.  You can see some additional details here:

http://www.appliedbiosystems.com/absite/us/en/home/applications-technologies/solid-next-generation-sequencing/next-generation-systems/solid-sequencing-chemistry.html