Carbon Dioxide Responsive Polymer Colloids

 The next generation of advanced materials will be capable of responding to variation in their environment by undergoing changes in their chemical or physical properties. The stimulus to which the materials react is known as a “trigger”, and such materials are commonly known as “stimuli-responsive” materials. This research examines a new type of polymer nanoparticles. These are very small particles (~100 nm in diameter, or 1000x smaller than the thickness of a human hair) that find application in a wide range of products, many of significant economic importance to Canada, including for example coatings, sealants, adhesives, personal/health care products and cosmetics. What we will do is develop new methods for making these nanoparticles stimuli responsive, so that the particles will undergo a desirable or beneficial change in their properties upon exposure to a trigger that will make them more useful or valuable for a given application. Well known examples of stimuli-responsive materials include windows that darken upon exposure to bright light or respond to changes in pH or temperature. In collaboration with Professor Philip Jessop, we have developed polymer nanoparticles that can undergo a dramatic change in properties upon exposure to simple, benign triggers; carbon dioxide or air. In contrast, other existing stimuli-responsive polymer particles require toxic chemicals such as strong acids or bases to switch. We need only bubble carbon dioxide or air into a water-based suspension of our particles to switch their surface properties so that the particles exist either as a uniform dispersion (under carbon dioxide) or as an aggregated powder (under air). This is achieved because the particle surface electrical charge can be “switched”. We have developed processes for making three different types of carbon dioxide responsive nanoparticles. One type uses free radical polymerization, an  established chemistry commonly used in existing products. The  second type uses a novel chemistry (controlled radical polymerization) suitable for advanced, high valued added applications. The third type features a novel, switchable renewable nanomaterial derived from cellulose, known as CNC (cellulose nanocrystals).

Stimuli-responsive materials are currently the subject of intense research interest because of their potential for application in both commodity and high value added materials. They have significant potential for advancing several industries in which they are already widely used, as well as being a cornerstone for new products and applications.

Dispersion of carbon dioxide switchable latex particles under CO2 atmosphere (A) showing well-dispersed stable particles, and under air (B) where the particles are no longer stable but settle under gravity.