Scalable Synthesis of Multifunctional Epidermis‐Like Smart Coatings

Abstract

Bioinspired self-healing materials provide a sustainable solution for mitigating catastrophic failure and prolonging service time, but such potential may be largely offset by the tedious fabrication process that can hardly be scaled up. It is shown that a scalable doctor blade coating process may be used for the synthesis of multifunctional epidermis-like smart coatings. The industry-compatible technique not only preserves the biomimetic bilayer design with largely improved film production efficiency but also allows readily adjusted film compositions and structures for optimizing the synergetic healing performance and mechanical properties. Variable amounts of montmorillonite clay nanosheets can be incorporated in the top hard layer for achieving a high modulus (34.3 ± 1.4 GPa) and hardness (1.65 ± 0.09 GPa), which also affect the number of scratch-healing cycles by controlling the decay rate of upward polymer diffusion from the soft bottom layer. These high-performance smart coatings are transparent, bactericidal, and show good adhesions to various substrates including glass, plastics, and fiberboard. When used as a surface protection for fiberboard, excellent flameretardant properties are demonstrated thanks to the dominant presence of clay nanosheets. It is believed that this work may provide important guidance for transforming interesting biomimetic design into practical manufacturing.

A Self-Strengthening Epidermis-Like Smart Coating Enabled by Dynamic Iron Sequestration

“…The details about the preparation of MTM, PVA-TA and PVA-TA-MTM solutions can be found in our previous work. 22 100 μL of PVA-TA solution was carefully dropped and spread evenly onto Q235 steel (coverage area of 1 cm 2 ) via doctor blade coating process, then the liquid film was dried at 70 °C for 20 min to obtain (PVA-TA)1.…”

“…To mimic the iron uptake mechanism in mussels, an open system that can continuously sequester ions from the environment is needed. For this purpose, the epidermis-like smart coating (ELSC), which consists of polyvinyl alcohol (PVA) and tannic acid (TA) as the thick bottom layer (60 μm) and the additionally added montmorillonite (MTM) nanosheets as the thin top layer (2 μm), 22 is applied on a steel sheet (Q235) by a rapid scalable doctorblade coating technique ( Figure 1a). Such bilayer design as (PVA-TA)1@(PVA-TA-MTM)1, where the subscript denotes the times of the coating applied, mimics the stratified structure of human epidermis and allows the integration of enamel-like hardness with self-healing ability of skin as recently demonstrated in our previous work.…”

“…Such bilayer design as (PVA-TA)1@(PVA-TA-MTM)1, where the subscript denotes the times of the coating applied, mimics the stratified structure of human epidermis and allows the integration of enamel-like hardness with self-healing ability of skin as recently demonstrated in our previous work. 22,23 Different from the inert substrate such as glass, the steel is used as a sustained ion supply and the coated steel is placed into water with different concentrations of sodium chloride (NaCl) as the stimulus to trigger the iron sequestration ( Figure 1a). While the yellowish color of the bilayer coating hardly changes in pure water for 100 days, those placed in saltwater have obviously changed their colors ( Figure 1b).…”

“…This is likely because the upwards polymer diffusion from the bottom to the top layer is gradually reduced due to the introduction of more coordination bonds, eventually resulting in insufficient polymer supply (Figure 4b) corresponding to a largely reduced kin (diffusion coefficient into the top layer). 22,23 Such effect may be partially mitigated by increasing the thickness of bottom layer so that a longer complete self-healing becomes possible (Supporting Information Figure S7). On the other hand, the self-healing performance of bottom layer alone shows an opposite trend (Figure 4c).…”

Ferric Ions Modified Polyvinyl Alcohol for Enhanced Molecular Structure and Mechanical Performance

“…PVA has excellent mobility, which is usually used to penetrate the surface of porous materials and to form smooth and stable bond lines. This makes it a common component in coatings and adhesives for paper and wood-based materials [9,10]. When used as an adhesive alone, the bonding strength of pure PVA is usually vulnerable to damage.…”