In this blog post, we’ll explore the principles, manufacturing methods, pros and cons, and various applications of fingerprint-resistant films that apply the lotus leaf effect.
The Lotus Effect and Its Principles
As technology has advanced, daily life has become so dependent on cell phones that it would be inconvenient without them. With just a single cell phone, you can stay in touch with friends, use the internet, play games, and perform virtually any function typically associated with a computer. However, in the past, fingerprints would remain on the screen every time you touched it, requiring frequent wiping—a real inconvenience. Recently, “fingerprint-resistant films,” which prevent fingerprints from easily sticking to the surface, have become widely used to reduce this inconvenience.
The core principle behind these fingerprint-resistant films is the “Lotus Effect.” Lotus leaves are characterized by their ability to remain dry even when water droplets land on them; the droplets maintain their round shape and roll off the surface. This is due to the countless microscopic, nano-sized protrusions formed on the surface. These microstructures prevent water droplets from spreading across the entire surface and significantly reduce the contact area between the water and the surface, allowing the droplets to roll off easily.
A key concept here is surface tension. Surface tension is the force that minimizes the surface area of a liquid, causing water droplets to maintain as round a shape as possible. A classic example of this phenomenon is when a toothpick or needle is carefully placed on water and does not sink. This is possible because the molecules on the liquid’s surface strongly attract one another, creating surface tension.
Furthermore, the nano-scale protrusions on lotus leaves create superhydrophobic properties. The angle formed between a water droplet and a surface is called the contact angle; generally, if the contact angle is less than 90 degrees, the surface is classified as hydrophilic, and if it is greater than 90 degrees, it is classified as hydrophobic. On a superhydrophobic surface, the contact angle can reach 150 degrees or more; as a result, water droplets do not spread out widely but maintain a nearly spherical shape and roll off easily.
Manufacture and Applications of Anti-Fingerprint Films
By utilizing this lotus-leaf effect, special nanoparticles can be coated onto the surface of a smartphone screen to form a structure of microscopic nano-protrusions. On such a surface, the actual contact area with fingers or contaminants is greatly reduced, preventing fingerprints and dirt from easily adhering.
Various inorganic nanoparticles are used in anti-fingerprint films, with titanium dioxide (TiO₂) and silica (SiO₂) based coating technologies being the most widely used. Various manufacturing processes are employed, including low-temperature spray coating, sol-gel coating, and plasma coating, and the appropriate process is selected based on the product’s intended use and manufacturing method.
Low-temperature spray coating is a technique that uses a supersonic airflow generated by compression and expansion to propel powder particles at high speeds onto the substrate surface. Since this method allows processing at relatively low temperatures, it minimizes material deformation and thermal damage. It is widely used across various industries due to its advantages in enhancing wear resistance, corrosion resistance, heat resistance, and fatigue resistance.
However, anti-fingerprint films also have drawbacks. The microscopic nano-textured structure formed on the surface can, in some cases, scatter light, slightly reducing screen clarity or visibility. To address this, various technologies have recently been developed to more precisely control the nanostructure, thereby increasing light transmittance and maintaining screen clarity. For example, technologies that simultaneously ensure anti-fingerprint performance and high transparency by making the surface nearly smooth—through more uniform control of the size and spacing of the nanostructures—are now being commercialized.
The lotus leaf effect is utilized in various fields beyond anti-fingerprint films. Waterproof clothing and paper, water-repellent coatings for automotive glass, stain-resistant architectural exterior materials, self-cleaning glass, and non-stick frying pan coatings are all representative examples that apply this superhydrophobic principle.
In other words, materials engineering is the discipline that develops new materials to solve the inconveniences of daily life and applies them to various products. Just as diverse applied technologies are derived from a single fundamental principle, the lotus leaf effect is also being widely utilized in everything from everyday household items to cutting-edge industrial materials, and materials engineering has established itself as a crucial foundational discipline that underpins various fields of science and engineering.
