Additives in Smart Coatings

Smart coatings are formulations that are able to respond to various performance challenges due to changes in the coating's environment after application. These challenges may include color changes, self-cleaning, hygienic functions and self-healing due to physical damage.

Key to these coating performance characteristics is the combination of additives that have been integrated into a formulation in such a way that the desired properties are exhibited as required. Although not always optimum in their global application, additives that control pigment color characteristics, resin chemical reactivity, the controlled release of chemical components, and film electrochemical characteristics represent general descriptions for the function of these additives.

An example of these additives is nano-scale machines. These devices may provide a monitored electronic signal that is dependent on the specific condition of the coating film. Detected emitted signals can trigger initiating a variety of protocols related to maintaining the integrity of the coating film or enhancing its performance. Such functions include corrosion protection and the initiation of specific coating maintenance procedures.

Another example is encapsulated monomer/ polymer systems designed to have multiple-time-release capability that allow the physical repair of a damaged applied coating. The possible combination of direct coating physical changes and nano-sensor response can trigger capsule release of a monomer/polymer to repair physically damaged films. Similarly, micro-encapsulated/nano-scale colorants or temperature/electronic signal-sensitive, liquid-crystalline additives can permit coating color changes on demand.

More Smart Coatings

Sensor coatings fall into the category of smart coatings. When applied to a substrate, the coating film can chemically participate with species already present on the substrate or react with chemical components that subsequently contaminate the film. In many instances, such coatings contain polymer combinations as well as additives such as plasticizers, chelating agents and indicators.

In a surface decontamination application, these coatings consist of strippable polymeric compositions containing blends of polymers, copolymers and additives that can be brushed or sprayed onto a surface as a solution or dispersed in aqueous media. Upon curing or drying, these coatings form films that can be easily removed from the surface. When applied to a contaminated surface, these coatings display responsive color change due to chemical interaction with the contaminant. As the coating dries, the contaminant is drawn into the polymer matrix and fixed. Subsequent removal of the coating with entrapped contaminants results in measurable surface decontamination.

As an example, coatings that consist of the additive combination of hydrolyzed polyvinyl alcohol, poly(vinyl pyrrolidone), glycerin, EDTA, ethanol and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol serve as a detector/indicator for Hg contamination on substrates.

Making Coatings More Green

Major focuses for enhancing the environmentally friendly characteristics of coatings include the production of cleaner coatings, the design of formulations that allow beneficial recycling of coating waste and the application of coatings with reduced volatile organics.

For example, formulation approaches that utilize powder and pigment slurries, powder coatings, dendrimeric resins, metal-containing oligomers and radiation-cure resins permit the development of more environmentally friendly coatings. The coordinated use of additives such as acid-stable oligomeric, biodegradable dispersants support the use of coating systems with high functionality and low viscosity at high molecular weight, enhanced adhesion, ideal pigment dispersion and good film-flow properties in aqueous media.