Design, Synthesis, and Characterization of Bioinspired Functional Coatings and Adhesives

Catechol-based molecules have been identified as one of the key elements responsible for many important functions in natural systems owing to their intrinsic physicochemical properties. Capitalizing on these universal design principles found in nature, catecholic molecules have been increasingly considered in the field of materials science as possible bioinspired structural motif candidates to synthesize and fabricate advanced engineering materials. This thesis begins with a short introduction to the structural diversity of the most important families of catecholic molecules found in biological systems, with an emphasis on elucidating the structure-property relationships arising from the chemical functionalities present in their molecular structures. In chapter 1 the fundamental physicochemical interactions undertaken by catecholic molecules at interfaces, both in nature and in bioinspired materials, and common strategies for productive manipulation of these interactions are further described. Chapter 2 aims to provide a more complete picture of marine mussel adhesion, particularly at the molecular level, and facilitate developing a solid framework for the rational design of mussel-inspired wet adhesives. In this chapter the interplay between chemical sequence and topological structure in the mussel adhesive proteins is illustrated by highlighting the results of our molecular level study on the interfacial adhesion of a library of mussel-inspired peptides to organic and inorganic substrates. In chapters 3-6 a summary of the research on design, synthesis, and characterization of catechol-based bioinspired functional materials for implementation in diverse applications ranging from hybrid materials and coatings to high-performance dry/wet adhesives is provided. In chapter 3, bioinspired catechol-based material polydopamine (pDA), one of the most widely employed surface modification methods due to its versatility and simplicity, is introduced and the results of the research undertaken to elucidate the formation mechanism, structure, and molecular mechanics of this fascinating material is discussed. In chapter 4 some of the main shortcomings of these coatings including their poor mechanical performance are described followed by reporting a simple post-treatment approach via thermal annealing at a moderate temperature as a facile route to enhance mechanical robustness of pDA coatings without compromising their inherent functionality. A suite of characterization techniques are employed and analysis of the results shows fundamental changes in the molecular and bulk mechanical behavior of pDA after thermal annealing, leading to considerable improvements in the ability of the coatings to resist mechanical deformations. Chapters 5 and 6 describe developing catechol-based pressure-sensitive adhesives (PSAs) by exploiting the mussel adhesion principles. In chapter 5 a combination of microscopic and macroscopic adhesion assays are used to study the effect of catechol on dry and wet adhesion performance of the catechol-containing PSAs. Chapter 6 describes developing a new generation of synthetic amino-catechol adhesives inspired by the adhesive synergy between flanking amine and catechol residues in the mussel adhesive proteins. Comprehensive multi-scale adhesion characterization is used to probe performance at the molecular, microscopic, and macroscopic levels, showing that coupling of catechols and amines together within the same hybrid monomer architecture produced optimal cooperative effects in improving macroscopic adhesion performance.

Advisor: Messersmith, Phillip B