AN EXPERIMENTAL INVESTIGATION ON THE STRUCTURE OF MICROCAPSULES

Newly prepared microcapsules with diameters of the order of 0.1 mu m h ave been investigated by means of static and dynamic laser light scatt ering, synchrotron small-angle X-ray scattering (SAXS), viscosimetry, and electron microscopy. The microcapsule has a core of phosphoric aci d, bis(2 3-dibromopropyl)-2,3-dichloropropyl ester, and a wall compose d of polyurethane-urea. The dispersing medium (H2O) contains copoly(vi nyl alcohol-vinyl acetate) which acts as a protective colloid. Static light scattering and SAXS give the same z-average radius of gyration R (g) 110 nm in the concentration range of 1 x 10(-5)-5 x 10(-4) g/cm(3) for lightscattering and of 1 x 10(-3)-0.14 g/cm(3) for SAXS. The hydr odynamic radius R(h) = 143 nm as determined by dynamic Light scatterin g is close to the viscosity radius R(eta) = 151 nm obtained from intri nsic viscosity measurements of the microcapsule suspension. By assumin g the microcapsule as a solid sphere, the radius of gyration estimated from R(h) was R(g,cal) = 0.78R(h) = 112 nm. The agreement of R(g) and R(g,cal) as well as R(h) and R(eta) strongly suggests that in wet for m, the protective colloid has stuck tightly onto the surface of the mi crocapsule. The number-average radius R(n) obtained from electron micr oscopy was 65 nm. The radius of gyration calculated from the size dist ribution based on electron microscopy wasR(g,cal,e) = 91 nm, being sli ghtly smaller than those obtained in the wet state.