Mechanical strength of single microcapsules determined by a novel micromanipulation technique

A micromanipulation technique has been developed to measure the bursting force of single dry microcapsules coated onto a surface, such as those normally used in carbonless copying paper. For measuring the bursting force of a given microcapsule, a single fine probe with a flat end about 10 μm in diameter was used to squeeze the microcapsule against a flat surface until it burst. The force being imposed on the microcapsule was measured by a transducer connected to the probe. The bursting force and diameter of single dry microcapsules in two samples, different in size and wall thickness, were measured by this technique. The bursting force of the microcapsules in one sample ranged from 50 to 220 μN and the diameter from 1.3 to 7.0 μm, whilst the bursting force in the other was from 20 to 175 μN and the diameter from 0.7 to 3.7 μm. This technique makes it possible to compare the mechanical strength of microcapsules made of different formulations, and to infer information about microcapsule mechanical properties.