Robust Composite-Shell Microcapsules via Pickering Emulsification

Abstract

Microencapsulation technology has been increasingly applied toward the development of self-healing paints. Added to paint as a dry powder prior to spraying, the microcapsules store a liquid that can repair the protective barrier layer if released into a scratch. However, self-healing will not occur unless the microcapsules can withstand spray-painting, aggressive solvents in the paint, and long-term exposure to the elements. We have therefore developed a one-pot synthesis for the production of Pickering microcapsules with outstanding strength, solvent resistance, and barrier properties. Octadecyltrimethoxysilane-filled (OTS) microcapsules form via standard interfacial polycondensation, except that silica nanopowder (10-20 nm diameter) replaces the conventional surfactant or hydrocolloid emulsifier. Isophorone diisocyanate (IPDI) in the OTS core reacts with diethylenetriamine, polyethylenimine, and water to form a hard polymer shell along the interface. Compared to pure polyurea, the silica-polyurea composite improves the shelf life of the OTS by 10 times. The addition of SiO2 prevents leaching of OTS into xylenes and hexanes for up to 80 days, and the resulting microcapsules survive nebulization through a spray gun at 620 kPa in a 500 cSt fluid.

Polymer–silica hybrid self-healing nano/microcapsules with enhanced thermal and mechanical stability

“…Compared to ceramics and metals, the shell walls of the nanocapsules formed by polymer materials are generally fragile and have elastic modulus around 1-2 GPa. 24 So far, the mechanical properties of a single nanocapsule have rarely been studied.…”

“…The interfacially active solid particles adsorbed at the interface between the two phases increase the stability of the emulsion through steric repulsion. 24 Aer interfacial polymerization on the Pickering emulsion template, the organic-inorganic hybrid capsule shell can be obtained. The shell wall of microcapsules composed of solid particles can improve the resistance and strength of the microcapsules, encapsulating more active core materials.…”

Chemically stable polyphenylene ether microcapsules prepared using a facile method for the self‐healing of polymers

“…The introduction of healing agent‐filled microcapsules (MCs) to polymer materials is a very effective approach for healing damage (e.g. cracks or scratches) under controlled conditions, and can realize the restoration of mechanical properties (e.g. tensile strength, fracture toughness and interfacial shear strength), electrical properties, etc .…”

Preparation of uniform poly(urea–siloxane) microspheres through precipitation polymerization

“…20 Furthermore, they display an irreplaceable role in a number of material areas as they are finely dispersed in polymer matrices to improve their mechanical properties. 21 Studies have been conducted on the fabrication of various types of polysiloxane spheres, namely polysiloxane spheres modified or coated by other species, [22][23][24] organic and inorganic particles modified or coated by polysiloxane, [25][26][27] and interpenetrating polysiloxane/polymer spheres. 28 However, these spheres were obtained by multistep process, in which silicone parts are often prepared by hydrolytic polycondensation of trialkoxysilanes or trichlorosilanes.…”