Adhesion and interfacial healing between supramolecular hybrid networks and glass substrates

Adhesion towards glass and interfacial healing of partially supramolecular hybrid polymer networks featuring a range of H-bdnds content were investigated through two dedicated adhesion test methods. In a first series of tests, adhesion strength was measured by separating two substrates containing a cured inner resin layer, and shown to decrease with increasing H-bonds content in the polymer network (from 0 to 50%) as the mechanical strength of the polymer also decreased while the failure mechanism shifted from adhesive to cohesive due to the possibility to form hydrogen bonds with glass substrates. In a second step, the test was used to evaluate interface restoration through healing of the polymer matrices and results showed an increased from none to a tensile strength recovery up to 70% after 1 h healing time for the 50% H-bond polymer. Then, self-adhesion of freshly cut polymer surfaces to glass substrates was investigated, showing increasing tack with increasing H-bonds content. The influence of glass surface treatments on adhesion and interfacial recovery properties was also explored: while aminosilanes did not influence the interfacial behavior of partially supramolecular self healing polymers towards glass, trimethoxy (octadecyl)silane (ODS) modification strongly hindered their adhesion abilities, further highlighting the fundamental role of hydrogen bonds interaction with the substrates.

Self-Healing Fiber-Reinforced Composites with Tailored Supramolecular Matrices

Federica Sordo

Fiber Reinforced Composites (FRCs), due to their intrinsic heterogeneity, are generally affected by complex multi-scale failure mechanisms leading to the formation of matrix cracks that are difficult to detect and repair. FRCs with the ability to heal and recover at least part of their initial properties after damage could present a solution to extend their lifetime and reliability. A possible approach is to introduce external healing agents in the matrix of the composite, through capsules or micro-channels, but this is often difficult to achieve in a high volume fraction reinforcement composite. An alternative approach is to rely on intrinsic self-healing polymers as matrices, which alleviates the need for additional phases beyond matrix and reinforcement. The present work investigated this second approach, by exploring for the first time the feasibility of processing glass fabric reinforced composites based on supramolecular hybrid network self-healing matrices and analysing their resulting properties and transfer of the self-healing ability to the composite. Hybrid networks based on epoxy chemistry, combining covalent cross-links and cooperative reversible hydrogen bonds, were selected as benchmark materials. These systems were charac- terized, in particular in terms of processing parameters and self-healing ability, and showed to be a-priori compatible with FRCs manufacturing techniques and demonstrated higher healing efficiency by increasing the H-bonds content in the polymer network, from none to 50%. On the other hand, networks characterized by large number of physical cross-links exhibited limited solvent and creep resistance, hindering their potential application. These issues were addressed by modifying the average functionality of the monomers through the combination of bifunctional and tetrafunctional epoxy resins in the compositions while keeping the use of a catalyst, leading to better controlled networks, both in terms of kinetics and final structure, and to propose a range of materials with several levels of compromise between self-healing efficiency, mechanical strength, creep resistance, and damping properties. In particular, 50% to 100% self-healing recovery of tensile properties were observed after one day, depending on the tetraepoxide content. In parallel, since the Tg of benchmark supramolecular hybrid net- works was in the range from 11-16 âŠC, an aliphatic diepoxide was introduced in the synthetic procedure to propose materials with a Tg down to -10 âŠC, to reach applications closer to those of elastomers. In view of FRCs development, the ability of partially supramolecular self-healing polymers to bond to inorganic reinforcements and to heal interfacial failure was then investigated: two dedicated butt joint-like and tack-like test methods were developed. Adhesion strength of the polymers cured on glass substrates decreased with increasing H-bonds content in the polymer networks (from 0 to 50 %) as the mechanical strength of the polymer also decreased, while the failure mechanism shifted from adhesive to cohesive due to the possibility to form hydrogen bonds with the glass substrates. Interface restoration through healing of the polymer matrices however increased from none to a strength recovery up to 70 % after 1 h healing time for the 50% H-bond polymer...

EPFL2016

Multicomponent Assembly of Macrocycles and Polymers by Coordination of Pyridyl Ligands to 1,4-Bis(benzodioxaborole)benzene

Burçak Içli, Benan Kilbas, Rosario Scopelliti, Kay Severin, Euro Solari

Multicomponent reactions between 1,4-benzenediboronic acid, catechol, and different pyridyl ligands are reported. The condensation of 1,4-benzenediboronic acid with catechol gives 1,4-bis(benzodioxaborole)benzene. Upon crystallization, the ester aggregates with the N-donor ligands through dative BN bonds. Depending on the nature of the pyridyl ligand, molecularly defined macrocycles or polymeric structures are obtained. 1D polymers are formed with 4,4-bipyridine and 1,2-di(4-pyridyl)ethylene, whereas a 2D network is obtained with the tetradentate ligand tetra(4-pyridylphenyl)ethylene. These results highlight the utility of dative BN bonds in structural supramolecular chemistry and crystal engineering.

Wiley-V C H Verlag Gmbh2012

Multicomponent Assembly of Boronic Acid-Based Macrocycles, Cages, and Polymers

Burçak Içli

This work describes the synthesis and characterization of boronic acid-based supramolecular structures. Different reversible interactions such as boronate ester formation, imine condensation and dative B–N bond formation are used to assemble macrocycles, cages and polymers. Multicomponent condensation reactions of different diamines with tetraols and formylphenylboronic acids give macrocycles via formation of imine bonds and boronate esters. The [4+2+2] condensation products are generally preferred but larger macrocycles are observed for some combinations of staring materials. The larger macrocycles are in dynamic equilibrium with the smaller [4+2+2] products. Utilization of a triamine instead of the diamine results in the formation of molecular cages. The syntheses of these cages require the formation of 18 covalent bonds between 11 building blocks, and, interestingly, can be performed in a ball mill. Multicomponent reactions of diboronic acids, catechol derivatives, and different pyridyl ligands are described. The condensation of diboronic acids with catechols gives dioxaboroles. Upon crystallization, the ester aggregates with the N-donor ligands via dative B−N bonds. Depending on the nature of the pyridyl ligand, molecularly defined macrocycles, cages or polymeric structures are obtained. One-dimensional polymers are formed with 4,4-bipyridine and 1,2-di(4-pyridyl)ethylene, whereas a two-dimensional network is obtained with the tetradentate ligand tetra(4-pyridylphenyl)ethylene. A tripyridyl linker results in the formation trigonal prismatic cages. The size of the cages can be varied by changing the diboronic acid building block. The cages are able to encapsulate polyaromatic molecules such as triphenylene or coronene. The results highlight the potential of dative B−N bonds in structural supramolecular chemistry and crystal engineering.

EPFL2012

Self-Healing Fiber-Reinforced Composites with Tailored Supramolecular Matrices

Federica Sordo

EPFL2016