Improvement in Cohesive Properties of Adhesion Systems Using Movable Cross-Linked Materials with Stress Relaxation Properties

A strong, tough, and stable adhesion system used in various environments must be developed. A long-lasting adhesion system should effectively perform in the following five aspects: adhesion strength, toughness, energy dissipation property, self-restoration property, and creep resistance property. However, these properties are difficult to balance using conventional adhesives. Here, a new topological adhesion system using single-movable cross-network (SC) materials [SC(DMAAm) Adh] was designed. 3-(Trimethoxysilyl) propyl acrylate was used as the anchor, N,N-dimethyl acrylamide (DMAAm) was used as the main chain monomer, and γ-cyclodextrin (γ-CD) units acted as movable cross-links. The movable cross-links provided SC(DMAAm) Adh with energy dissipation properties, thereby improving its toughness. The γ-CD units also acted as bulky stoppers that provided a high adhesion strength and self-restoration properties. Moreover, the combination of the movable cross-links and bulky stoppers provided creep resistance to SC(DMAAm) Adh. The performance of the adhesion systems under different mobilities of the polymer chains was examined by adjusting the water content. In proper water-containing states, all mechanical properties of SC(DMAAm) Adh were better than those of the adhesion systems using homopolymers [P(DMAAm) Adh] and polymers with covalent cross-linking points [CP(DMAAm) Adh].

Intrinsically Photopolymerizable Dynamic Polymers Derived from a Natural Small Molecule

Developing photopolymerizable polymeric materials offers many opportunities to process materials in a remote and controllable manner. However, most photopolymerizable technologies require the external introduction of photoabsorbing units, whereas designing intrinsically photopolymerizable polymers is still highly challenging. Here, we report that a natural small-molecule disulfide, thioctic acid, can be directly transformed into a poly(disulfides) network under the irradiation of visible light without any external additives. The resulting polymer network exhibits optical transparency, mechanical stretchability and toughness, ambient self-healing ability, and especially strong adhesive ability to different surfaces. The dynamic covalent backbones of the poly(disulfides) endow the depolymerization ability to recycle the material in a closed-loop manner. We foresee that this facile and robust photopolymerization system is of great promise toward low-cost and high-performance photocuring coatings and adhesives.

A supramolecular polymer with ultra-stretchable, notch-insensitive, rapid self-healing and adhesive properties

Supramolecular elastomers, possessing excellent mechanical, reusable adhesivity, and rapid self-healing properties, are essential for use in various applications.

Multifunctional coatings combining bioactive peptides and affinity-based cytokine delivery for enhanced integration of degradable vascular grafts

Mussel-derived surface coatings present integrin- and heparin-binding peptides for cell adhesion and modulator protein delivery to improve the endothelialization of biodegradable cardiovascular implants.

Supramolecular silicone coating capable of strong substrate bonding, readily damage healing, and easy oil sliding

Polymer coatings with a combined competence of strong bonding to diverse substrates, broad liquid repellency, and readily damage healing are in substantial demand in a range of applications. In this work, we develop damage-healable, oil-repellent supramolecular silicone (DOSS) coatings to harvest abovementioned properties by molecular engineering siloxane oligomers that can self-assemble onto coated substrates via multivalent hydrogen bonding. In addition to the readily damage-healing properties provided by reversible association/dissociation of hydrogen bonding motifs, the unique molecular configuration of the siloxane oligomers on coated substrates enables both robust repellency to organic liquids and strong bonding to various substrates including metals, plastics, and even Teflon. We envision that not only DOSS coatings can be applied in a range of energy, environmental, and biomedical applications that require long-term services in harsh environmental conditions but also the design strategy of the oligomers can be adopted in the development of supramolecular materials with desirable multifunctionality.

Bioinspired Underwater Adhesives by Using the Supramolecular Toolbox

Nature has developed protein-based adhesives whose underwater performance has attracted much research attention over the last few decades. The adhesive proteins are rich in catechols combined with amphiphilic and ionic features. This combination of features constitutes a supramolecular toolbox, to provide stimuli-responsive processing of the adhesive, to secure strong adhesion to a variety of surfaces, and to control the cohesive properties of the material. Here, the versatile interactions used in adhesives secreted by sandcastle worms and mussels are explored. These biological principles are then put in a broader perspective, and synthetic adhesive systems that are based on different types of supramolecular interactions are summarized. The variety and combinations of interactions that can be used in the design of new adhesive systems are highlighted.

Carbohydrate-Responsive Surface Adhesion Based on the Dynamic Covalent Chemistry of Phenylboronic Acid- and Catechol-Containing Polymer Brushes

A glue, based on dynamic covalent chemistry, with a strong adhesion (2.38 kg cm^-2 ), water resistance and carbohydrate responsive reversibility is presented. Using surface initiated atom transfer radical polymerization (SI-ATRP), glass and silicon surfaces were coated with copolymers functionalized with phenylboronic acids and catechols. In combination with microcontact printing (μCP) these polymer brushes give access to a carbohydrate responsive "supramolecular Velcro".

CH/π Interactions for Macroscopic Interfacial Adhesion Design

Adhesion to chemically inert materials without surface modification through noncovalent interactions represents a challenging task in adhesion science. We successfully develop for the first time a strategy utilizing multiple CH/π interactions that use poly(methacrylate) with an aromatic group (H acceptor) in the ester part and polyolefin materials (H donor). The strength increases with the number of π electrons and aromatic rings. The trityl methacrylate polymer emerges as the most effective H-acceptor polymer for obtaining strong adhesion to various polyolefin materials. This work will provide not only a promising adhesion strategy that does not require surface activation for polyolefin materials, but also a novel approach using weak noncovalent interactions.

Supramolecular polymer adhesives: advanced materials inspired by nature

Due to their dynamic, stimuli-responsive nature, non-covalent interactions represent versatile design elements that can be found in nature in many molecular processes or materials, where adaptive behavior or reversible connectivity is required. Examples include molecular recognition processes, which trigger biological responses or cell-adhesion to surfaces, and a broad range of animal secreted adhesives with environment-dependent properties. Such advanced functionalities have inspired researchers to employ similar design approaches for the development of synthetic polymers with stimuli-responsive properties. The utilization of non-covalent interactions for the design of adhesives with advanced functionalities such as stimuli responsiveness, bonding and debonding on demand capability, surface selectivity or recyclability is a rapidly emerging subset of this field, which is summarized in this review.

The leading role of cation–π interactions in polymer chemistry: the control of the helical sense in solution

Cation–π interactions determine the helical sense adopted by a polyphenylacetylene bearing (R)-α-methoxy-α-phenylacetamide as a pendant group (poly-1).

Ion enrichment on the hydrophobic carbon-based surface in aqueous salt solutions due to cation-π interactions

By incorporating cation-π interactions to classic all-atoms force fields, we show that there is a clear enrichment of Na⁺ on a carbon-based π electron-rich surface in NaCl solutions using molecular dynamics simulations. Interestingly, Cl⁻ is also enriched to some extend on the surface due to the electrostatic interaction between Na⁺ and Cl⁻, although the hydrated Cl⁻-π interaction is weak. The difference of the numbers of Na⁺ and Cl⁻ accumulated at the interface leads to a significant negatively charged behavior in the solution, especially in nanoscale systems. Moreover, we find that the accumulation of the cations at the interfaces is universal since other cations (Li⁺, K⁺, Mg²⁺, Ca²⁺, Fe²⁺, Co²⁺, Cu²⁺, Cd²⁺, Cr²⁺, and Pb²⁺) have similar adsorption behaviors. For comparison, as in usual force field without the proper consideration of cation-π interactions, the ions near the surfaces have a similar density of ions in the solution.