Mechanical strength of single microcapsules determined by a novel micromanipulation technique

A micromanipulation technique has been developed to measure the bursting fo rce of single dry microcapsules coated onto a surface, such as those normal ly used in carbonless copying paper. For measuring the bursting force of a given microcapsule, a single fine probe with a flat end about 10 mu m in di ameter was used to squeeze the microcapsule against a flat surface until it burst. The force being imposed on the microcapsule was measured by a trans ducer connected to the probe. The bursting force and diameter of single dry microcapsules in two samples, different in size and wall thickness, were m easured by this technique. The bursting force of the microcapsules in one s ample ranged from 50 to 220 mu N and the diameter from 1.3 to 7.0 mu m, whi lst the bursting force in the other was from 20 to 175 mu N and the diamete r from 0.7 to 3.7 mu m. This technique makes it possible to compare the mec hanical strength of microcapsules made of different formulations, and to in fer information about microcapsule mechanical properties.