Droplet coalescence near liquid/liquid critical points

The state of matter within a fluid layer near a critical point differs profoundly in many aspects from states further removed from the critical point. The interfacial tension tends to vanish, the interface thickens, and long-range concentration fluctuations exist. Because of these effects, critical phenomena have been investigated as possible sources of instability in thin films. Shear-field coalescence studies have been performed between phases of a simple ternary system containing no surfactant as a function of distance from a critical point. The coalescence efficiency was measured as a function of temperature through time dependent photomicrographic analysis of emulsion samples within a shear-field coalescence cell. The apparatus, procedure, and analysis are outlined. No evidence was found for the promotion of coalescence by critical phenomena for values of reduced temperature, T_r = (T - T_c)/T_c, down to 4×10^-4.