Kimio Ichikawa

Release characteristics of an azo dye from poly(ureaurethane) microcapsules.

The time course for the transfer of azo dyes from the microcapsule core of dioctylphthalate to the dispersing medium of methanol through a poly(ureaurethane) (PUU) membrane was measured for various average size microcapsules with a size distribution. The dye release curves are represented by a stretched exponential function C(t)=C(eq)[1-exp [-(t/tau(eff))(alpha)]], where C(t) is the concentration of the dye in methanol, C(eq) that at the equilibrium state, and t the time. The exponent alpha decreased by increasing the variance of the size distribution of microcapsules. The effective time constant tau(eff) was expressed by tau(eff)=c(0)/kappa(alpha), where and kappa(alpha) are the mean square of microcapsule radius and a correction for the size distribution, respectively. The characteristic proportional constant, c(0), was determined as 2.6+/-0.2 min/microm(2). From the value of the constant, the diffusion coefficient of the azo dye in the PUU membrane was evaluated as 2.6 x 10(-12) cm(2)/s.

Permeability of azo-dye through poly(urea-urethane) microcapsule membrane

Abstract Transfer of azo-dyes from dioctylphthalate to methanol through poly(urea-urethane) microcapsule (PUUMC) membrane has been measured. The release curves are expressed by an exponential equation Cs=C∞(1−e−t/τ), where Cs is the concentration of the dye in methanol, C∞ that at the equilibrium state, t the elution time and τ is a time constant. C∞ and τ are related to the chemical potentials and the diffusion coefficient of the dye, based on a simple theoretical model. The relationship between τ and the absolute temperature exhibits non-Arrhenius behavior at high temperatures. The non-Arrhenius behavior is explained on the basis of the chemical potential effect on τ. At low temperatures, τ exhibits the Arrhenius behavior. From a semi-logarithmic plot of τ versus the reciprocal of the absolute temperature in the low temperature region, the activation energy for the transfer of the dye is estimated.

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: where C(t) and Ceq 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.