Switchable Surfactants for Preparation of Stimuli-Responsive Polymer Nanoparticles

Project Background
Co-PI: Dr. Philip G. Jessop, Queen's University, Chemistry Department
A switchable surfactant is defined as a surfactant that can be reversibly converted into a molecule with greatly reduced or even negligible surface activity, upon application of a trigger. In order for the surfactant to be truly switchable, the inactive form of the molecule must be convertible back into the surface-active form by the application of another trigger or removal of the first trigger. The proposed work will explore switchable surfactants as a new approach to surfactant design that will facilitate emulsion breaking, surfactant separation, and even (in some applications) surfactant recycling. Most importantly, the switchable surfactants will use inexpensive and safe reagents to trigger the switching of the surfactant; these triggers will be carbon dioxide and nitrogen or air.

This project will investigate a new class of “smart” or stimuli-responsive materials; substances that undergo a dramatic change in chemical or physical properties in response to a change in their local environment.1-5 Such materials are increasingly being used as smart sensors, as diagnostic devices and in advanced manufacturing applications where a desired change in the behaviour of a substance can be readily triggered using simple means. We intend to develop polymer nanospheres (<1 micron in diameter) that can reversibly switch from being uniformly suspended in a liquid (water or oil based) to an aggregated state comprising polymer particles and clear liquid. The particles will aggregate upon exposure to air, and redisperse (if desired) upon exposure to carbon dioxide, an environmentally benign trigger.

The switchable surfactants to be evaluated in this work uses carbon dioxide as the trigger for switching on the surface activity and are switched off (or switched into a demulsifier form) by flushing the system with nitrogen or air in order to remove the carbon dioxide from the system. Some proposed structures (e.g. Scheme 1) are amidines, guanidines, and possibly primary, secondary, or tertiary long-chain amines, which react with carbon dioxide in the presence of water to generate bicarbonate salts. As long as one of the R groups is a long hydrophobic chain, then the bicarbonate salt should have surface activity.

Scheme1 project2

Figure2 project2