An Experimental Investigation on the Structure of Microcapsules

Abstract

Newly prepared microcapsules with diameters of the order of 0.1 {mu}m have been investigated by means of static and dynamic laser light scattering, synchrotron small-angle X-ray scattering (SAXS ), viscosimetry, and electron microscopy. The microcapsule has a core of phosphoric acid, bis(2,3-dibromopropyl)-2,3-dichloropropyl ester, and a wall composed of polyurethane-urea. The dispersing medium (H{sub 2}O) contains copoly(vinyl alcohol-vinyl acetate) which acts as a protective colloid. Static light scattering and SAXS give the same z-average radius of gyration R{sub g} = 110 nm in the concentration range of 1 x 10{sup -5} - 5 x 10{sup -4} g/cm{sup 3} for light scattering and of 1 x 10{sup -3} - 0.14 g/cm{sup 3} for SAXS. The hydrodynamic radius R{sub h} = 143 nm as determined by dynamic light scattering is close to the viscosity radius R{sub {eta}} = 151 nm obtained from intrinsic viscosity measurements of the microcapsule suspension. By assuming the microcapsule as a solid sphere, the radius of gyration estimated from R{sub h} was R{sub g,cal} = 0.78R{sub h} = 112 nm. The agreement of R{sub g} and R{sub g,cal} as well as R{sub h} and R{sub {eta}} strongly suggests that in wet form, the protective colloid has stuck tightly ontomore » the surface of the microcapsule. The number-average radius R{sub n} obtained from electron microscopy was 65 nm. 18 refs., 7 figs., 2 tabs.« less