3 research outputs found
Synergy between Galvanic Protection and Self-Healing Paints
Painting is a cost-effective technique
to delay the onset of corrosion
in metals. However, the protection is only temporary, as corrosion
begins once the coating becomes scratched. Thus, an increasingly common
practice is to add microencapsulated chemical agents to paint in order
to confer self-healing capabilities. The additive’s ability
to protect the exposed surface from corrosion depends upon (i) how
long the chemical agent takes to spread across the exposed metal;
(ii) how long the agent takes to form an effective barrier layer;
and (iii) what happens to the metal surface before the first two steps
are complete. To understand this process, we first synthesized 23
± 10 μm polyurea microcapsules filled with octadecyltrimethoxysilane
(OTS), a liquid self-healing agent, and added them to a primer rich
in zinc, a cathodic protection agent. In response to coating damage,
the microcapsules release OTS into the scratch and initiate the self-healing
process. By combining electrochemical impedance spectroscopy, chronoamperometry,
and linear polarization techniques, we monitored the progress of self-healing.
The results demonstrate how on-demand chemical passivation works synergistically
with the cathodic protection: zinc preserves the surface long enough
for self-healing by OTS to reach completion, and OTS prolongs the
lifetime of cathodic protection
Robust Composite-Shell Microcapsules via Pickering Emulsification
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 SiO<sub>2</sub> 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