Rapid self-healing capability as a metric for flexible spacing coating toward macroscopic supramolecular assembly of rigid building blocks

Macroscopic Supramolecular Assembly of Rigid Building Blocks Facilitated by Layer-By-Layer Assembled Microgel Film

“…In order to understand the underlying assembly mechanism of MSA facilitated by the microgel films, we characterized the compliance of the (PAH/AA-microgel) n films with varied bilayer number via atomic force microscopy (AFM) force measurements. According to our previous reports, , the elastic modulus of building blocks could be a metric to determine whether the compliance of coatings is sufficient for MSA because the surface deformability is essential to trigger multivalent interfacial binding. Hence, we measured Young’s modulus of (PAH/AA-microgel) n films to quantify the film compliance when varying the bilayer number.…”

“…Similar to hydrogel materials, microgel particles are promising for use in MSA because designated supramolecular functional groups can be programmed into microgel particles during the synthesis stage, − which may enrich application scenarios for MSA due to advantages of microgels’ porous structures and stimulus-responsiveness properties. − It is worth noting that LbL-assembled microgel films have been reported to heal micrometer-sized defects upon exposure to water , because of the high softness and flowability, which is significant features of flexible spacing coating for the MSA process . In this work, the LbL-assembled microgel films composed of negatively charged poly­( N -isopropylacrylamide- co -acrylic acid) microgels (AA-microgel) and a polycation of poly­(allylamine hydrochloride) (PAH) are modified onto rigid millimeter-scaled PDMS building blocks to act as both a flexible spacing coating and a supramolecular interactive surface for assembly of rigid building blocks.…”

“…40−43 It is worth noting that LbL-assembled microgel films have been reported to heal micrometer-sized defects upon exposure to water 44,45 because of the high softness and flowability, 46 which is significant features of flexible spacing coating for the MSA process. 33 In this work, the LbL-assembled microgel films composed of negatively charged poly(N-isopropylacrylamideco-acrylic acid) microgels (AA-microgel) and a polycation of poly(allylamine hydrochloride) (PAH) are modified onto rigid millimeter-scaled PDMS building blocks to act as both a flexible spacing coating and a supramolecular interactive surface for assembly of rigid building blocks. The results demonstrate that the MSA probability of oppositely charged PDMS building blocks displays a positive dependence on the number of microgel bilayers.…”

“…To this end, quite a few works employ highly flowable soft hydrogels as building blocks to demonstrate the MSA process based on various supramolecular interactions such as host–guest recognition, − electrostatic interactions, ,− hydrogen bonding, − metal–ligand interactions, ,, and complementary nucleobase interactions. , The supramolecular moieties can be covalently grafted or physically mixed into the matrix during the fabrication of hydrogel building blocks instead of post-modification; however, the building blocks are restricted to soft, low-modulus hydrogel systems, thus having limited the potential functional applications of macroscopic assemblies. For high-modulus non-hydrogel materials, a concept of ‘flexible spacing coating’ is proposed as an effective strategy to promote the mobility of the surface and enhance the binding strength, having addressed the problem that rigid building blocks cannot achieve MSA of building blocks only modified with interactive supramolecular groups. − Taking advantage of layer-by-layer (LbL) methods irrespective of materials, size, and shape of substrates, , a composite polyelectrolyte multilayer is pre-modified on the surface of macroscopic rigid building blocks as a flexible spacing coating to improve the compliance of the original surface, and thus, the post-modified supramolecular groups with enhanced mobility can interact with each other to stably bind two macroscopic surfaces of diverse rigid materials, including elastomer, resin, metal, and glass, and so forth. Namely, the proposed strategy of flexible spacing coating can overcome the problem of MSA being limited to soft hydrogel materials following a tedious and time-consuming two-step modification process to induce a flexible spacing coating and subsequent supramolecular recognition groups.…”

Robust Electrostatically Interactive Hydrogel Coatings for Macroscopic Supramolecular Assembly via Rapid Wet Adhesion

“…The macroscopic supramolecular assembly (MSA) refers to a self-assembly of micrometer-to-millimeter building blocks based on multivalent non-covalent interactions − and has developed rapidly toward the goal of “self-assembly at all scales” by bridging the molecular assembly behaviors to the macroscopic materials. Owing to the characteristics of interfacial interactions between micrometer-to-millimeter surfaces, studies of the MSA mechanism are used to understand diverse non-covalent interfacial phenomena such as bio-/wet adhesion, , self-healing. − Meanwhile, MSA has been developed as a facile modular fabrication strategy to prepare heterogeneous structures, bio-scaffolds, , actuators, and information storage materials. − To extend the applicable scenarios of MSA, much progress has been achieved on enriching supramolecular interactions (molecular recognition, , hydrogen bonding, electrostatic interactions, DNA hybridization, , and so on), extending building block materials (gels, ,,− , elastomers, ,, quartz, and metal) that could realize MSA, and revealing the assembly mechanism. ,,, These studies have demonstrated that MSA is not simply an amplification of the building block size from the molecular self-assembly but requires additional factors (e.g., external energy and fast interfacial adhesion) to facilitate the binding of two macroscopic surfaces. In a typical MSA process, micrometer-to-millimeter building blocks are placed in water and extra shaking or rotation is necessary to trigger the interactions, during which the collision frequency is much lower than that of molecular thermal motions.…”