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Silica-shell/oil-core microcapsules with controlled shell thickness and their breakage stress.

The encapsulation of one material by another, to form core-shell particles (microcapsules), has many applications, principally the containment, protection, and distribution of an active material. This work describes the development of core-shell particles with silicone oil cores and solid silica-like shells of controlled thickness. Oligomeric polydimethylsiloxane (PDMS) emulsions are employed as the core templates for the formation of the solid shells. The core templates are prepared by the surfactant-free, condensation polymerization of diethoxydimethylsilane (DEODMS) that leads to the formation of monodisperse silicone oil/water emulsions. Solid silica-like, composite shells were formed through condensation of tetraethoxysilane (TEOS) and DEODMS onto the core templates. The shell thickness may be controlled by manipulation of relative TEOS and DEODMS concentrations or by quenching the shell development step. It is possible to incorporate a dye into the core prior to shell formation, which does not seem to permeate the shell. The coated PDMS particles were subjected to a controlled compression stress using a micromanipulation technique. The capsule breaking force was found to be proportional to the shell thickness, as quantified using scanning electron microscopy (SEM) ultramicrotomy.