Fast, Localized, and Low-Energy Consumption Self-Healing of Automotive Clearcoats Using a Photothermal Effect Triggered by NIR Radiation

Abstract

Dynamic polymer networks containing photothermal materials have been reported to demonstrate highly efficient intrinsic self-healing under irradiation. In particular, organic near-infrared-absorbing ionic salts, such as diimmonium dyes, function as transparent polymer heaters and can enhance the self-healing properties of clearcoats. In this study, we designed a self-healing automotive clearcoat with a reversible polymer network based on acryl polyol (AP) and dynamic hindered urea (HU) bonds and introduced N-butyl-substituted diimmonium borate dye (DID) as a photothermal dye. To optimize the self-healing efficiency of the clearcoat and its transparency in the visible light region, the effects of the presence or absence of dynamic HU bonds and the concentration of the photothermal dye were precisely investigated. For a polymer system containing HU with 0.1 wt % DID (AP/HU-DID_0.1), the transparent automotive clearcoat was heated to ∼70 °C under focused sunlight irradiation and exhibited excellent (∼100% healing efficiency) and fast (<30 s) scratch-healing performance compared with a commercial automotive clearcoat. In addition, this photothermal effect-based self-healing clearcoat exhibited outstanding transparency (over 95%) and has a strong advantage with respect to energy consumption because it enables faster and more localized healing compared with thermal healing processes that require heating the entire product.

NIR-Triggered High-Efficiency Self-Healable Protective Optical Coating for Vision Systems

“…56 More recently, our group introduced a self-healing automotive clearcoat containing an organic photothermal dye and showed that the clearcoat can be activated by sunlight. 46 Among these systems, photothermal self-healing is advantageous over other mechanisms in that it provides a fast and highly efficient self-healing process of the hard coating (>10 3 MPa in indentation hardness and modulus) by elevating the surface temperature of the coating in response to a specific adsorption band in sunlight. However, there is a limitation in controlling the optical properties of aliphatic self-healing poly(urethane acrylate)s because their refractive indexes inherently converge at ∼1.5.…”

“…When a self-healable optical protective coating is applied directly to an optical lens surface with various ranges of refractive power, it is highly desirable for the refractive index conditions of the self-healable coating material to be controllable over a wide range to avoid generating stray light between adjacent optical layers. In most outdoor applications, autonomous self-healing capability under ambient sunlight conditions is better for energy efficiency and user convenience and safety . The self-healing function needs to be achievable for deeply scratched surfaces or those with random multiple surface damages.…”

“…Similarly, Jung et al developed a polymer coating that self-repairs via a change in the lower critical solution temperature (LCST) trigged by atmospheric CO 2 and H 2 O . More recently, our group introduced a self-healing automotive clearcoat containing an organic photothermal dye and showed that the clearcoat can be activated by sunlight . Among these systems, photothermal self-healing is advantageous over other mechanisms in that it provides a fast and highly efficient self-healing process of the hard coating (>10 3 MPa in indentation hardness and modulus) by elevating the surface temperature of the coating in response to a specific adsorption band in sunlight.…”

“…In most outdoor applications, autonomous self-healing capability under ambient sunlight conditions is better for energy efficiency and user convenience and safety. 46 The selfhealing function needs to be achievable for deeply scratched surfaces or those with random multiple surface damages. Importantly, in addition to self-healing functions, the surface coating hardness should be high as an external protective coating layer.…”

Design of Eco-Friendly Self-Healing Polymers Containing Hindered Urea-Based Dynamic Reversible Bonds

“…The motivation for self-healing materials comes from the self-repair characteristic of natural materials, such as healing of damaged skins of trees and animals. Various self-healing polymers (SHPs) have been developed, shifting engineering problems from maintenance related to recycling, thereby lowering the overall costs of processing and mechanical failure in different industrial processes. − SHPs are smart materials that can heal and restore their properties when aided by the required external stimulus such as radiations, temperature, pH, and magnetic field. , In the most recent years, ultrafast recovery systems have been made from these SHPs which have been successfully utilized as wearable electronics, cut-detecting sensors, automotive coatings, and many more. − …”