Color Tunable Ultrathin Films Capable of Healing Multiple Scratches

Abstract

Healable films with structural color are highly desirable and have a variety of potential applications. However, combining structural color with self-healing properties to obtain new functional materials is a big challenge in current research. Herein, we present the first example of a color tunable, ultrathin film that can self-heal in response to external mechanical abrasion. It is designed based on intermolecular hydrogen bonding interaction; the synthetic strategy involves spin-coating of poly(acrylic acid) (PAA) and chitosan (CS). The successful preparation of ultrathin, healable, structural color films provides a new type of biomimetic material.One of the characteristic features of living systems is structural color, which can be detected in the outer shells of jewel beetles, wings of butterflies and on many other insects.[1] The structural color originates from spectrally selective reflection of visible light from a periodic modulation of refractive index rather than pigment, dye or luminescence. Inspired by natural biological structures, photonic crystals (PhCs), which are composite structures with a periodic arrangement of refractive index in one dimension, [2] two dimensions, [3] and three dimensions, [4] have been designed and fabricated. Recently, they have been gradually applied in a myriad of applications such as optical devices, [5] sensing materials, [6] display technologies, [7] solar cells [8] and so on. [9] One-dimensional photonic crystals (1DPhCs) have the simplest structures and are easy to handle because of their simple structures composed of alternately stacked thin-film layers with high and low refractive indices. [10] The dynamic coloration is generally achieved either by changing the thickness of the multilayers or the refractive index of individual layers through chemical reactions. [11] Although PhCs have substantial potential applications in the development of advanced functional materials, accidental scratches on optical films change the way light is transmitted and can even cause severe light scattering. Such scratches on optical films have to be healed to restore their original optical functions for further applications.[12] Ideally, if we can mimic the living biological systems more closely and endow the materials with self-healing properties, the designed materials will have extended service lives, which can facilitate their maintenance and increase their reliability with stable functionality. [13] However, combining structural color with self-healing property is an enormous challenge, and there is no report on this field to date.In general, polymers have great potential for self-healing due to the high mobility of the polymer chains under physiological conditions. Polyelectrolyte multilayers have a pronounced self-healing effect due to their mobility in response to environmental change. External stimuli such as pH, ionic strength, temperature, light, etc. affect ionization of the functional groups of the polyelectrolytes, which makes the polyelectrolyte multilayers st...

An antibacterial and biocompatible multilayer biomedical coating capable of healing damages

“…24 Comparative observation of the black line and red line with the blue line (CS/ CMC multilayer polyelectrolyte coating) revealed that it can be found that the absorption peaks of the amino and carboxyl groups shied, which indicates that CS and CMC interact through hydrogen bonding. 25 The hydrogen bonding can undergo a reversible "break-rebuild" process under certain stimulation conditions, which is suitable for the designing of new stimulus-response materials. Recently, a lot of new functional materials with self-healing property were constructed through hydrogen bonding; for example, Sun et al have successfully constructed a coating material with excellent selfhealing performance based on the hydrogen bonding between bPEI and PAA.…”

Bioinspired structural color nanocomposites with healable capability

“…35,36 When being applied in daily life, colloidal PCs are likely to be handled via physical mechanisms, which in turn can bring the possibility of damage to the delicate periodic nanostructures, leading to the failure of the optical and/or structural properties. 37,38 Therefore, improving the mechanical strength of colloidal PC materials has been one of the critical aspects to ensure the durability and stability of PCs. To this end, several strategies have been employed for the construction of mechanically robust colloidal PCs.…”

Photopatternable Nanolayered Polymeric Films with Fast Tunable Color Responses Triggered by Humidity

“…Due to this versatility, LbL films have been designed to incorporate responsive polymers to respond to a wide range of external changes in pH, ionic strength, temperature, solvation, light, enzyme, and electrochemical and mechanical loads . There are, in fact, three reasons LbL assembly is considered an effective way to produce nanofilms that could generate tunable structural colors: i) The stepwise deposition allows precise control of film thickness in the length scale of visible wavelength (hundreds of nanometers); ii) postmodification of the chemical compositions of LbL film offers the possibility for surface patterning, and iii) the dynamic response of LbL films provides the potential to achieve real‐time tenability …”