Silica-Shell/Oil-Core Microcapsules with Controlled Shell Thickness and Their Breakage Stress

Abstract

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.

Preparation of microencapsulated medium temperature phase change material of Tris(hydroxymethyl)methyl aminomethane@SiO2 with excellent cycling performance

“…Because of the ionization of -NH 2 , the concentration of OH À in water layer near the interface increases, resulting in a suitable pH value for hydrolysis and polycondensation of the silicon precursors. Analogous to the phenomena reported in previous studies [53][54][55], the amount of APTS concentration in the bicomponent precursors is important for the formation of the silica shell. When the ratio of TEOS to APTS is 20 mL:5 mL, particles with regular sphere shape can be obtained (Fig.…”

Aqueous dispersions of silica shell/water-core microcapsules

“…This is straightforward when the continuous phase is aqueous, where, in principle, the interfacial condensation reaction should continue until all the added monomer is reacted. Hence, as the current authors have shown [1], relatively thick silica shells may be formed (although if the concentration of monomer initially is too high, secondary condensation reactions may occur, producing silica particles in solution). However, if the continuous phase is oil, and the dispersed phase is the aqueous one, then the monomer and water molecules have to react across the interface to produce the solid shell.…”

“…Under basic or acidic conditions an interfacial condensation reaction occurs at the PDMS/water interface, leading to silica-based shells up to $0.1 lm in thickness. A linear correlation was found [1] between the breakage force of the shells and their thickness. Also, it was found [1] that dye molecules could be solubilised into the PDMS liquid cores, prior to shell formation, and that the dye did not leak out into the continuous phase from the microcapsules dispersed in water.…”

“…In a recent paper from this group [1] we describe the preparation of liquid core/solid shell particles (microcapsules), in which the liquid core was oligomeric poly(dimethylsiloxane) (PDMS) and the shell was silica-based. These core-shell particles were prepared from oil/water (O/W) emulsions containing monodisperse, surfactant-free PDMS droplets [2,3], which were encapsulated using alkoxysilanes, or mixtures of alkoxysilanes, added to the continuous aqueous phase [1,[4][5][6].…”

“…These core-shell particles were prepared from oil/water (O/W) emulsions containing monodisperse, surfactant-free PDMS droplets [2,3], which were encapsulated using alkoxysilanes, or mixtures of alkoxysilanes, added to the continuous aqueous phase [1,[4][5][6]. Under basic or acidic conditions an interfacial condensation reaction occurs at the PDMS/water interface, leading to silica-based shells up to $0.1 lm in thickness.…”