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In the world of material science – how does one extend a material’s functional lifetime? The field of self-healing materials is pursuing one solution to this question as scientists and engineers, inspired by the self-healing properties of the biological world, work to develop material systems that can automatically repair themselves without human inspection or intervention. Several classes of self-healing materials include self-healing polymers (SHP), self-healing electronics (SHE), and self-healing ceramics (SFC). Across each family of materials, the self-healing capabilities are created using the same general approach. All the necessary materials to repair structural damage are embedded within the original material matrix. In doing this the purpose is to recover the original material properties. Within the realm of defense applications one can imagine the potential self-healing materials hold – high temperature SHCs for aircraft engines1, anti-icing SHP skins for UAV aircraft2, anti-fouling SHP coatings that could increase fuel efficiency in naval ships3, and robust, printable, SHE circuits that can rapidly heal macroscopic cracks4.
Herein the general principle behind self-healing materials is reviewed before highlighting technologies that enable deeper investigations of the underlying self-healing mechanisms.
The general approach to self-healing systems is to embed all the necessary materials to repair structural damage within the original material matrix and recover the original material properties.5 Then, upon injury or damage, a triggering event initiates material transport into the damage site where a chemical repair process can take place (Figure 1). The resultant chemical repair mechanism could include polymerization, polymer cross-linking, hydrogen or ionic bonding interactions, amongst many other mechanisms.
Figure 1. Illustration of the general process behind self-healing materials.
Several ways of distributing the “self-healing” components involve embedding micro-capsules in the material matrix, the use of 1D-3D vascular networks, or through the use materials that intrinsically bond or re-organize within the matrix (ex. hydrogen or polymer cross-linking). All of these rely, in their own way, on chemical mobility and chemical interactions to fill the damaged volume and recover the original material properties. A wide variety of optical tools (imaging and spectroscopy) exist to uncover the mechanism and relevant timescales of the various healing methods for different material compositions. Representative examples of these methods include the use of optical microscopy and Raman spectroscopy to monitor the self-healing dynamics6 and tease out the mechanism of chemical reactions that could underpin a healing mechanism7.
Andor Imaging and Spectroscopy Solutions: Andor provides a diverse array of technological solutions for imaging and spectroscopy studies of self-healing systems from the soft X-ray to SWIR wavelengths (0.1 – 2500 nm). The core technologies for optical inspection of self-healing systems require quantitative cameras and spectrographs.
For robust characterization of material healing, such as humidity driven self-healing of cracks,6 scientific CMOS (sCMOS) imaging cameras provide high fidelity, quantitative measurements. Characteristic to sCMOS technology is its fast frame rates, providing access studying the dynamics of material recovering on millisecond to second time scales. This is accomplished without compromising on sensitivity (QE as high as 95%), noise levels (read noise as low as 0.9 e-), dynamic range, or resolution. In real, experimental, terms these features mean detecting more photons and resolving finer features with good contrast. These cameras are available across the soft X-ray to SWIR wavelength range with our Marana-X providing sensitivity in the soft X-ray and EUV region; the CB2-UV camera providing sensitivity across the UV; our CB2 visible series, Marana, ZL41 Wave cameras enabling sensitive detection in the visible, and our C-Red camera line providing measurement capabilities in the NIR and SWIR wavelength regions up to 2.2 µm.
Mechanistic studies of self-healing materials based on spectroscopic methods require a spectrograph, to disperse the light, and a camera to record the dispersed light as a function of wavelength. Examples of relevant spectroscopic methods include Raman spectroscopies (both non-resonant and resonant forms) which can yield valuable information, such as the role that metal coordination can play in polymer cross-linking that influences polymer cross-linking.8 Andor’s spectrographs and spectroscopy cameras easily enable researchers to perform accurate and reproducible spectroscopy experiments including Raman, Non-linear, LIBS, and Luminescence measurements, to name a few. Our spectrographs provide a modular platform that can be configured exactly to the users’ needs and include a number of features aimed at delivering the highest resolution possible. Coupled with our CCD, EMCCD, or sCMOS cameras, photons spanning the UV to SWIR can be detected with high sensitivity down to single-photon sensitivity for visible-NIR wavelengths.
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