Preface

Nature first created materials capable of responding to CO₂ in the form of stomata: CO₂-switchable pores that regulate the flow of gases and moisture. It was only recently that humans began taking an interest in designing materials capable of undergoing useful changes in their chemical or physical properties in response to changes in CO₂ concentration. In the past decade, interest in CO₂-switchable materials has surged, fuelled by scientists in diverse fields of research discovering new uses for existing CO₂-switchable materials or creating new switchable materials, often at the nanoscale. Why has there been such an explosion of interest in CO₂-switchable materials? This book explores that question and hopefully provides the reader with an understanding of current developments in the field as well as an appreciation for the opportunities and environmental benefits offered by commercialization of CO₂-switchable materials.

For the past two decades, stimuli-responsive materials have attracted widespread interest among scientists and engineers, and numerous products based on different stimuli or triggers have successfully found their way into the marketplace. Commonly recognized triggers include light, voltage, and temperature. In contrast, the stimuli-responsive materials described in this book use CO₂ as the trigger. CO₂ possesses key advantages in triggering property changes, while overcoming many of the disadvantages of other triggers. CO₂-switchability has been designed into solvents, surfactants, catalysts, polymers (both synthetic and natural), and a broad range of surfaces. Nano-structured objects including spherical particles, vesicles, and worm-shaped tubes have been reported. Remarkably, many of these nano-objects can reversibly undergo self-assembly and disassembly upon the addition or removal of CO₂. The potential for CO₂-switchable materials to favourably impact the environment is considerable, and is the primary driving force for the development of CO₂-switchable materials. We anticipate that commercial CO₂-switchable materials will replace existing technologies that lack the energy- and materials-saving advantages offered by switchable materials.

We have written the book for a broad audience, including academic, government and industrial researchers, industrial practitioners, and graduate students. General introductions have been given for each topic to increase accessibility to nonspecialists, but we have also endeavoured to provide the reader with a detailed understanding of the fundamental principles underlying CO₂-switchability and the nature of the materials described.

Topics covered in the book include an introduction to the principles of CO₂ switching, switchable aqueous solutions and solutes, switchable organic solvents, switchable surfactants, the numerous types of CO₂-switchable particles, switchable surfaces and coatings, and switchable gels, microgels, and adhesives. Finally, we have included our personal perspective on the opportunities and challenges for CO₂-switchable materials. In each chapter we discuss potential environmental benefits and concerns for the materials presented in that chapter.

As a global society we are facing unprecedented challenges to preserving and restoring our environment. Demands for new products and increased consumption of all materials will continue to challenge our imagination and creativity in being able to satisfy those demands while minimizing environmental impact. The advent of CO₂-switchable materials presents a new opportunity to meet that challenge.

Philip G. Jessop and Michael F. Cunningham