The thickness δ of microcapsules consisting of a dioctyl phthalate core and an outer poly(urea-urethane) membrane has been determined by means of single-particle light scattering and the freeze-fracture method in combination with electron microscopy as a function of the dioctyl phthalate/wall-forming triisocyanate monomer volume ratio φ. The thickness δ increased nonlinearly with decreasing φ. The swelling ratio of the membrane was determined to be 1.2 in the range φ < 3, which was explained by the relatively low plasticizing effect of dioctyl phthalate.
Coexistence curves and turbidity of aqueous solutions of tetraoxyethylene mono-n-octyl ether C8E4 without and with the addition of urea were examined focusing on the critical behavior. The critical exponent β, which characterizes the shape of coexistence curve, for aqueous C8E4 solution was determined as 0.329±0.003 in agreement with 3D Ising model. Turbidity measurement for aqueous C8E4 solution also yielded Ising values γ=1.26±0.05 and ν=0.63±0.02 for the critical exponents of the isothermal compressibility and correlation length, respectively. Addition of urea up to 7 M concentration did not modify the critical exponents, although the critical temperature increased by about 20 °C with the addition of urea. Coexistence curves of oxyethylene mono-isobutyl ether C4E1 with the addition of 7 M urea also yielded β=0.326±0.002 in agreement with 3D Ising model. These are in contrast to our recent results that the critical exponents for heptaoxyethylene mono-n-tetradecyl ether C14E7 in an aqueous salt solution were modified to Fisher’s renormalized Ising values by the addition of salt [J. Chem. Phys. 109, 711 (1998)]. The difference in the critical behavior for the nonionic surfactant solutions might be attributed to the solution structure, structure of micellar aggregation of surfactant.
Microcapsules for internal radiation therapies containing the rare-earth metal elements Dy, Ho and Cu with a diameter of 5-10 microm were successfully obtained by an interfacial polymerization method and a successive sedimentation technique was employed to fractionate the microcapsules. A triisocyanate monomer and tricresylphosphate were used for a wall forming material and a core solvent for the metals, respectively. The amount of the metal elements loaded was measured using a high frequency plasma photoemission apparatus. The beta-ray radioactivity of 1 mg of microcapsules irradiated with a common neutron source is estimated as 370 microCi, which is satisfactorily strong for usual radiotherapy, when microcapsules containing Dy are used. Differential interference microscopy indicated narrow size distribution of the fractionated microcapulses.
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