Release behavior of W/O/W-type microcapsule

We have prepared W/O/W-type microcapsules with polyureaurethane wall membrane and aqueous core containing methylene blue by means of the double emulsification method and the effect of the rate of agitation at the twice emulsification on the release of methylene blue to dispersing methanol was examined. The release curve was expressed fairly well by the streched exponential form: (Equation presented) where C(t) and C _eq are the concentrations of methylene blue in the dispersing methanol at time t and at the equilibrium state, respectively. The time constant τ increased and the exponent α decreased with increasing the rate of agitation at the second emulsification, whereas τ decreased and α was constant with increasing the rate of agitation at the first emulsification. These differences are discussed from a viewpoint of inhomogeneity of the microcapsule wall membrane.