Molecular Interaction and Adhesion Mechanisms of Mussel-inspired Adhesive Coatings

• Author / Creator

  Xiang,Li

• In marine mussel adhesion science, mussel foot proteins (mfps) have been identified to play an essential role in forming the bioadhesive coating. A catecholic amino acid named 3,4-dihydroxyphenyl-L-alanine (DOPA) has been found to primarily contribute to such robust underwater adhesion performance by employing various catechol-modulated interactions including hydrogen bonding, coordination bonding, π-π stacking, cation-π interaction and covalent cross-linking. Based on these interactions, numerous underwater adhesives and coatings have been developed and applied for specific use purposes. Nevertheless, for synthetic adhesives, completely achieving adhesive coatings as robust as bioadhesvies is still a big challenge. Therefore, further studies on DOPA interfacial behavior is of great importance as it can provide both fundamental and practical insights into successfully translating Dopa chemistry to adhesion technology and engineering advanced materials. In this thesis, a surface forces apparatus (SFA) was applied to further explore the interaction mechanisms underlying mussel-inspired catecholic adhesion system, with specific focus on the roles of functional groups in mfps (e.g., catechol and amine), substrate surface chemistry (e.g., organic and inorganic surfaces) and water chemistry (e.g. salinity and salt type), and test the feasibility of potential coating strategies which may be utilized in surface functionalization under practical aqueous conditions.
  In the first work, a facile and versatile approach to prepare robust adhesive coating in aqueous solutions with high salinity and mild alkalinity was demonstrated through the incorporation of primary amines into polydopamine (PDA) during the polymerization of dopamine (i.e., catecholamine). SFA were applied to precisely quantify the interaction forces between PDA-amine adhesive coatings and investigate the impact of amine species amine content and water chemistry on the adhesion behaviour. The measured strong adhesion force was mainly achieved through the synergetic effect of amine and PDA, including the displacement of hydrated salt ions adsorbed on the surface by cationic amine, strong adhesion to substrate via catechol groups on PDA moieties and enhanced cohesion achieved by their cation-π interactions.
  In the second work, a study on the correlation between interaction behavior and deposition capability of DOPA-amine based adhesive coatings was conducted by virtue of SFA and AFM. Using tannic acid (TA) and diethylenetriamine (DETA) as the model catecholic moiety and amine, the mass ratio between catecholic moiety and amine was found to have a significant influence on the coating thickness, surface roughness and surface morphology during the deposition of adhesive coating through regulating the electric double layer (EDL) repulsion between as-formed TA-DETA aggregates. Such TA-DETA adhesive shown a strong adhesion to substrate surfaces bearing varies surface chemistry and wettability via multiple interactionsits because of its specific molecular structure and chemical properties, which was demonstrated to primarily contribute to the initiation of the formation of adhesive coating.
  In the third work, SFA and AFM were applied to directly quantify the correlation between the nanomechanics and deposition behavior of mussel-inspired polypyrocatechol (pPC) adhesive coatings in various monovalent saline aqueous media. For the first time, a different yet experimentally unexplored type of cation-π interaction with ternary π-cation-π configuration was identified. The ternary π-cation-π interaction was found to be able to induce the bridging effect of salt cation with two π-conjugated catechol groups, through which the monovalent cations actively participated in and greatly enhanced the wet adhesion and deposition of catechol-based adhesive coatings. By varying salt cation concentration, this ternary interaction could transform to a binary cation-π interaction at high cation concentration, leading to the abolishment of bridging and the undermined adhesion and deposition. Furthermore, such π-cation-π interaction behavior was demonstrated to be general for various cation species with the trend of binding strength following NMe4+ > K+ > Na+ > Li+.
  In the fourth work, a non-covalent interaction called anion-π interaction was experimentally identified for the first time, which was found to play a critical role in biomolecular underwater adhesion. The nanomechanics of anion-π interaction was directly quantified in a model system containing anionic phosphate ester and π-conjugated catecholic moieties which abound in marine bioadhesives, by using a surface forces apparatus with complementary computational simulations. Anion-π interaction, cooperated by cation-π interaction due to co-existence of cation, was unravelled to synergistically contribute to robust wet-adhesion. The anion-π interaction strength follows the trend of phosphate ester > HPO42- > SO42-> NO3-, affected by charge density, polarity and hydration effect.

• Subjects / Keywords

  • Mussel-inspired adhesive coatings
  • Intermolecular and surface forces

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-776m-dp52

• License

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