General Route for the Assembly of Functional Inorganic Capsules

Abstract

Semipermeable, hollow capsules are attractive materials for the encapsulation and delivery of active agents in food processing, pharmaceutical and agricultural industries, and biomedicine. These capsules can be produced by forming a solid shell of close packed colloidal particles, typically polymeric particles, at the surface of emulsion droplets. However, current methods to prepare such capsules may involve multistep chemical procedures to tailor the surface chemistry of particles or are limited to particles that exhibit inherently the right hydrophobic-hydrophilic balance to adsorb around emulsion droplets. In this work, we describe a general and simple method to fabricate semipermeable, inorganic capsules from emulsion droplets stabilized by a wide variety of colloidal metal oxide particles. The assembly of particles at the oil-water interface is induced by the in situ hydrophobization of the particle surface through the adsorption of short amphiphilic molecules. The adsorption of particles at the interface leads to stable capsules comprising a single layer of particles in the outer shell. Such capsules can be used in the wet state or can be further processed into dry capsules. The permeability of the capsules can be modified by filling the interstices between the shell particles with polymeric or inorganic species. Functional capsules with biocompatible, bioresorbable, heat-resistant, chemical-resistant, and magnetic properties were prepared using alumina, silica, iron oxide, or tricalcium phosphate as particles in the shell.

Porous Ceramics

“…The isoelectric point (IEP) is the pH at which a colloid's zeta potential is zero; it can be used to derive information about the pH ranges in which a colloid is stable. A suspension's pH can be modified to allow dissociated surfactant to adsorb electrostatically as counter ions onto oppositely charged alumina hydroxyl surface groups [39]. The suspension's inorganic particles can be stabilized in situ by the particles' hydrophobization with different colloidal particles containing predominantly -OH 2 + , -OH, and -O -surface groups.…”

Contact angle and adsorption behavior of carboxylic acids on α-Al2O3 surfaces

“…These surface-modified particles have received great interest in recent years [6], because of their ability to strongly attach to fluid-gas interfaces, enabling e.g., highly stable foams [7,8] and capsules [9].…”

Magnetic nanoparticles-induced anisotropic shrinkage of polymer emulsion droplets

“…[12][13][14] In this case, the occurrence of buckling will result in the formation of a hollow shell or capsule. 15,16 The wall consisting of colloidal particles was proven to have a reversible crumpling behavior by repeated compressing and expanding.…”