| Popis: |
Nature has been a source of inspiration for designing many new materials. A prevalent example is of mussel which has inspired the synthesis of adhesive polymers for biomedical application. The most common strategy is to incorporate the catechol groups present in the mussel foot proteins into the polymer adhesives. However, the role of individual chemical units such as aromatic group and two hydroxyl groups of the catechol molecule toward the adhesion of the polymers is not clearly understood. Thus, in order to explore the capabilities of mussel-based catechol moieties incorporated into the polymers in enhancing the polymer interfacial adhesion to a hydroxylated surface in dry and wet environments, we designed the polymers using controlled chemistry to vary the side groups selectively. Direct adhesion measurements of the polymers were done using the JKR adhesion test to minimize the contribution from the bulk as compared to commonly used lap-shear measurements. Attempts were made to connect the macroscopic adhesion of the polymers with the interfacial interaction strength of the model molecules or the polymers with the surface hydroxyl groups using surface sensitive sum-frequency generation spectroscopy (SFG). Additionally, molecular dynamics (MD) simulation were utilized to shed light on the physical picture of the interactions of molecules with the substrate.In the first study, polymers containing the functional groups with either only hydroxyl, only aromatic, or a combination of hydroxyl and aromatic groups representing four amino acids (Serine, Phenylalanine, Tyrosine, and Dihydroxyphenylanaline (DOPA)) were tested. The macroscopic JKR adhesion results of polymers were explained with the combination of SFG Spectroscopy and MD simulations results. The study helped to identify the contribution of hydroxyl and aromatic groups toward the interfacial adhesion in catechol based adhesives in dry conditions.In the second study, we tested catechol and protected catechol containing polymers to identify the role of catechol in interfacial adhesion in wet conditions. The macroscopic wet adhesion of the polymers was connected to information gained from SFG experiment, where we probed the contact interface between the polymer and sapphire substrate in the presence of water. This study explored the question of whether catechol can displace water and bond with hydrophilic surfaces.In the third study, we performed SFG along with MD simulations of liquid molecules in contact with sapphire to better understand the physical picture of interfacial interactions. The parameters affecting the interaction strength and their effect on the spectroscopic features were also investigated in this study.Thus, in this dissertation, we looked at the interfacial interactions using SFG and MD simulations to understand the macroscopic adhesion of mussel inspired hydrophobic adhesives. The work provides an understanding of the molecular interactions of the side groups and the correlation to the macroscopic adhesion. Additionally, in the context of mussel inspired adhesives, the role of hydrophobicity is signified as the critical component to remove the interfacial water. The work advances the understanding of nature-inspired adhesives and provides a framework for designing new adhesive materials. |
