English
Abstract
This paper focuses on the collaborative design of self-healing AR anti reflective and anti reflective films and superhydrophobic films to address the optical performance degradation, surface damage, and pollution issues faced by flexible display devices (including foldable screens) in practical use. By means of molecular structure design and nanocomposite technology, the integrated construction of two functional film layers is achieved, and their preparation process on flexible substrates is explored. The optical properties, hydrophobic properties, and self-healing properties of the co designed film layer under bending cycles are systematically tested. Research has shown that the collaboratively designed film layer maintains a transmittance of 92%, maintains a contact angle of over 155 °, and improves self-healing efficiency by 30% after a curvature radius of 5mm and 100000 bending cycles. This provides a new approach for optimizing the optical film performance of flexible display devices.
keywords
Self repair; AR anti reflective film; Superhydrophobic membrane; Flexible display devices; Bending durability
1. Introduction
With the rapid development of technologies such as 5G and artificial intelligence, flexible display devices (such as foldable screen phones and flexible OLED TVs) have gradually become the mainstream development direction in the display field due to their advantages of being lightweight, bendable, and portable. However, under frequent bending, external friction, and environmental erosion, the surface optical film of flexible display devices is prone to wear, scratches, contamination, and other problems, resulting in increased reflectivity and decreased transmittance, seriously affecting the display effect and device service life. Although traditional AR anti reflective and anti reflective films can improve optical performance, they lack self-healing ability and anti fouling performance; Although superhydrophobic membranes can resist stain adhesion, they are difficult to optimize optical performance. Therefore, the collaborative design of self-healing AR anti reflective and anti reflective films and superhydrophobic films is of great significance for improving the reliability and user experience of flexible display devices.
2、 Principles and Key Technologies of Collaborative Design
2.1 Principles of Collaborative Design
The collaborative design of self-healing AR anti reflective film and superhydrophobic film is based on the concept of functional complementarity and structural fusion. The self-healing function is mainly achieved by introducing dynamic covalent bonds (such as reversible disulfide bonds, hydrogen bonds) or shape memory polymers. When the film layer is damaged, the broken chemical bonds or deformed molecular chains can be recombined or restored to their original state under external stimuli such as heat, light, and humidity; The AR anti reflection function relies on the design of nanoscale microstructures and the use of low refractive index materials to reduce reflectivity through the interference and diffraction effects of light; The superhydrophobic performance is achieved by constructing micro nano composite rough structures and combining them with low surface energy materials such as fluoropolymers. Integrating three functions into the same film layer can enable flexible display devices to maintain high light transmittance while possessing the ability to self repair damage and resist stain adhesion, effectively improving bending durability.
2.2 Key Technologies
1. Molecular structure design: Polymers containing dynamic covalent bonds (such as polysulfides) are selected as self-healing matrices, and low refractive index siloxane segments and fluorinated groups are introduced into the molecular chains to achieve AR anti reflection and superhydrophobic functions, respectively. By adjusting the monomer ratio and polymerization process, optimizing the cross-linking density and flexibility of the molecular chains, the film layer maintains structural stability during the bending process.
2. Nanocomposite technology: Silica (SiO ?) nanoparticles are prepared by the sol-gel method, and their surfaces are modified with fluorosilane to make them both low refractive index and hydrophobic. The modified nanoparticles are uniformly dispersed in a self-healing polymer matrix to form a nanocomposite film layer. The presence of nanoparticles not only enhances the optical and hydrophobic properties of the film layer, but also serves as physical crosslinking points to improve the mechanical strength of the film layer.
3. Preparation process optimization: A synergistic design film layer was prepared on a flexible polyimide (PI) substrate using a spin coating thermal curing process. Accurately control the spin coating speed and time to ensure uniform film thickness (approximately 100-200nm); By stepwise heating and curing, cracks in the film layer can be avoided due to thermal stress. At the same time, plasma treatment technology is introduced to modify the surface of the PI substrate, enhancing the adhesion between the film layer and the substrate.
3、 Experimental Design and Performance Testing
3.1 Experimental Materials and Equipment
1. Materials: Polydisulfide monomer, 3-aminopropyltriethoxysilane, perfluorooctyltriethoxysilane, SiO ? nanoparticles, polyimide film (PI, thickness 50 μ m).
2. Equipment: Spin coater, thermosetting oven, Fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), contact angle measuring instrument, UV visible spectrophotometer, bending tester.
3.2 Performance Testing Methods
1. Optical performance testing: Use a UV visible spectrophotometer to measure the transmittance and reflectance of the film layer in the wavelength range of 400-700nm, and evaluate the AR anti reflection performance.
2. Hydrophobic performance test: Use a contact angle measuring instrument to measure the static contact angle and rolling angle of water droplets on the surface of the film layer. A contact angle greater than 150 ° and a rolling angle less than 10 ° are considered superhydrophobic.
3. Self repair performance test: Use a blade to create scratches on the surface of the film layer, and observe the scratch morphology through SEM; Place the damaged film layer in a 60 ℃ environment for 24 hours, measure the transmittance and contact angle of the scratch area again, and calculate the self-healing efficiency.
4. Bending durability test: Fix the prepared film PI composite sample on the bending test machine and perform cyclic bending under a curvature radius of 5mm. After every 10000 bending cycles, test the optical performance, hydrophobic performance, and self-healing performance of the film layer.
4、 Results and Discussion
4.1 Analysis of Film Structure and Morphology
FT-IR spectroscopy showed the successful introduction of characteristic absorption peaks of disulfide bonds (1030 cm ?¹), silicon oxygen bonds (1100 cm ?¹), and fluorinated groups (1200 cm ?¹) in the film layer, confirming the effectiveness of the molecular structure design. The SEM image shows that the modified SiO ? nanoparticles are uniformly dispersed in the polymer matrix, forming a micro nano composite rough structure with a surface roughness Ra of about 80-120nm, providing a structural basis for the superhydrophobic properties.
4.2 Performance of Collaborative Design Membrane Layer
1. Optical performance: In the visible light range, the transmittance of the co designed film layer reaches 95%, and the reflectivity is less than 1.5%, which significantly improves the performance compared to traditional AR anti reflective and anti reflective films. After bending 100000 times, the transmittance remained at 92%, indicating that the film layer can effectively maintain stable optical performance during flexible deformation.
2. Hydrophobic performance: The static contact angle of the membrane layer is 158 °, and the rolling angle is 5 °, exhibiting excellent superhydrophobic properties. After 100000 bending cycles, the contact angle decreased to 155 ° and remained superhydrophobic, indicating that the nanocomposite structure has good stability during the bending process.
3. Self repair performance: After 24 hours of repair at 60 ℃, the scratch on the non bent sample has a light transmittance recovery rate of 85% and a contact angle recovery of 153 °; After 100000 bending cycles, although the self-healing efficiency has decreased, it can still reach 70%, which is 30% higher than a single self-healing membrane layer. This is attributed to the synergistic effect of nanocomposite structures and dynamic covalent bonds. Nanoparticles act as physical supports to reduce the damage to chemical bonds caused by bending, while dynamic covalent bonds promote rapid repair of damaged areas.
4.3 Impact mechanism of bending durability
During the bending process, the film layer is mainly subjected to tensile, compressive, and shear stresses. In collaborative design of film layers, the nano composite structure enhances the mechanical strength of the film layer and disperses stress concentration; The reversible nature of dynamic covalent bonds enables the membrane layer to partially restore its molecular chain arrangement and reduce structural damage after being subjected to force deformation. In addition, the presence of superhydrophobicity reduces the erosion of the membrane layer by external pollutants, indirectly protecting the self-healing and AR anti reflection functions, thereby achieving synergistic stability of various properties under bending cycles.
5、 Challenges and Prospects
5.1 Challenges Faced
At present, the collaborative design of self-healing AR anti reflective and anti reflective films and superhydrophobic films still faces many challenges. Firstly, the integration of multiple functions leads to complex membrane preparation processes, high costs, and difficulty in achieving large-scale industrial production; Secondly, the self repair process requires strict environmental conditions, which limits its application in practical scenarios; In addition, the mechanism of fatigue damage accumulation in the membrane layer under long-term bending cycles is not yet clear and requires further in-depth research.
5.2 Development Prospects
Future research can be conducted in the following directions: firstly, developing green and low-cost preparation processes, such as using inkjet printing, roll to roll coating and other technologies to replace traditional spin coating processes; The second is to explore self-healing systems that do not require external stimuli, such as those based on nanocapsules or microbial induced self-healing mechanisms; The third is to combine molecular dynamics simulation and experimental research to reveal the bending fatigue damage mechanism and optimize the membrane structure design. Through interdisciplinary integration, it is expected to achieve widespread application of self-healing AR anti reflective and anti reflective films and superhydrophobic films in flexible display devices.
VI. Conclusion
This paper successfully achieved the collaborative design of self-healing AR anti reflective film and superhydrophobic film, and explored their bending durability in flexible display devices. The experimental results show that the co designed film layer exhibits excellent optical, hydrophobic, and self-healing properties, and can maintain good comprehensive performance even after 100000 bending cycles. This study provides new technical ideas for improving the performance of optical films in flexible display devices, which has important theoretical and practical significance for promoting the development of the flexible display industry.
