LIGHT-SCATTERING OF A SINGLE MICROCAPSULE WITH A HYDROGEL MEMBRANE

We have developed a light-scattering apparatus using a capillary tubin g sample cell that is particularly suitable for investigating the stru cture of a single microcapsule. This approach is capable of determinin g the individual structures of polydisperse particles because the scat tering function of each individual microcapsule can be measured indepe ndently. The apparatus was used to determine the outer diameter d and the membrane thickness delta of poly(L-lysine-alt-terephthalic acid) m icrocapsules as a function of pH. The values of both d and delta were found to be the lowest at pH 4 and increased as the pH value was shift ed to either side of pH 4. The change in delta was roughly proportiona l to the change in d, suggesting an isotropic volumetric phase transit ion of the hydrogel membrane of the microcapsule. Diffusion coefficien ts of anionic and cationic electrolyte ions in the microcapsule membra ne changed in parallel with delta.