Kinetics of Photochemical and Mechanochemical Organic Reactions on Surface

Solvents used in traditional chemical processes account for a large percentage of reaction mass and waste and can pose significant environmental and health risks. The environmentally friendly nature of mechanochemistry, in addition to other benefits, makes it a promising approach for sustainable chemistry over traditional solvent-based methods. However, it is still not a widely adopted method for performing chemical reactions on an industrial scale. This is partially due to the significant challenge associated with understanding the reaction kinetics under mechanochemical conditions. Many variations of scanning probe lithography (SPL) techniques are able to manipulate the organic molecules with precise control over force and position on surfaces, which offer unique opportunity to investigate the mechanochemical reactions at molecular level. Chapter 1 gives a review on recent advances in the application of SPL techniques in studying fundamental questions in mechanochemistry.

Polymer brushes, defined as thin polymer coatings in which individual polymer chains are tethered by one chain end to a solid interface. They are considered as the most powerful tools to interface properties. Potential applications of polymer brush patterns span a wide range from organic light emitting diodes (OLEDs) to membranes for desalination and gas separation, from tissue engineering to protein adsorption, controlled surface wettability and the study of fundamentals of cell biology. A number of controlled/“living” polymerization techniques, in particular those based on radical chemistry have been applied to generate such coatings on various types of substrates. It enables the grafting density, the thickness, and the chemistry of the coating to be manipulated very readily without altering the bulk mechanical properties of biomaterials. Responsive polymer brushes are a category of polymer brushes that are capable of conformational and chemical changes in response to external stimuli. They offer unique opportunities for the control of surface properties due to the precise control of chemical and structural parameters such as the brush thickness, density, chemistry, and architecture. In Chapter 2 we will discuss multiplexed stimuli responsive polymer brushes patterns that contain hidden information within the same area.

In Chapter 3 we apply novel printing platform to investigate the mechanosusceptibility of molecules to the applied mechanical energy. Mechanochemical solvent-free reactions by milling, grinding or other types of mechanical action have emerged as a viable alternative to solution chemistry. Mechanochemistry offers not only a possibility to eliminate the need for bulk solvent use, and reduce the generation of waste, but it also unlocks the door to a different reaction environment in which synthetic strategies, reactions and molecules previously not accessible in solution, can be achieved. We have used elastomeric tip arrays to precisely control the time and force applied between dienes and dienophiles on a surface to determine rate constants, activation energies and activation volumes for four reaction systems.