A bridge (30) comprises a first inlet port (31) at the end of a capillary, a narrower second inlet port (32) which is an end of a capillary, an outlet port (33) which is an end of a capillary, and a chamber (34) for silicone oil. The oil is density-matched with the reactor droplets such that a neutrally buoyant environment is created within the chamber (34). The oil within the chamber is continuously replenished by the oil separating the reactor droplets. This causes the droplets to assume a stable capillary- suspended spherical form upon entering the chamber (34). The spherical shape grows until large enough to span the gap between the ports, forming an axisymmetric liquid bridge. The introduction of a second droplet from the second inlet port (32) causes the formation of an unstable funicular bridge that quickly ruptures from the, finer, second inlet port (32), and the droplets combine at the liquid bridge (30). In another embodiment, a droplet (55) segments into smaller droplets which bridge the gap between the inlet and outlet ports.