title: Release characteristics of an azo dye from poly(ureaurethane) microcapsules.
abstract: 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)<R(2)>/kappa(alpha), where <R(2)> 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.
authors.affiliation: Department of Biological and Chemical Engineering, Faculty of Engineering, Gunma University, Kiryu, Japan.
authors.forename: Chih Pong
authors.initials: CP
authors.lastname: Chang
authors.forename: Takao
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Miho
authors.initials: M
authors.lastname: Kimura
authors.forename: Takashi
authors.initials: T
authors.lastname: Sato
authors.forename: Kimio
authors.initials: K
authors.lastname: Ichikawa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Dobashi
mesh_terms: D001391:Azo Compounds / Q000493:pharmacokinetics*; D002214:Capsules; D004396:Coloring Agents / Q000493:pharmacokinetics*; D011140:Polyurethanes / Q000493:pharmacokinetics*
chemical_list: D001391:Azo Compounds; D002214:Capsules; D004396:Coloring Agents; D011140:Polyurethanes