A laser-etched, AB-silicone film with sunlight-absorbing carbon nanotubes (CNTs) is designed to keep surfaces ice-free down to temperatures of -50°C.
The 'passive-active anti/de-icing film' could tackle the energy losses and mechanical safety risks that ice poses to wind turbines, power infrastructure and aircraft.
A team of researchers at both Jiangsu University of Science and Technology and Jilin University in China use a high-frequency nanosecond laser to carve a precise and microscopic grid of pillars into the composite material. This exposes the CNTs and creates a jagged and multiscale surface that acts as microscopic solar panels to trap incoming light and heat from the sun.
The pillars force water droplets to land on their tips and trap a pocket of air, which creates a barrier physically insulating the droplet from the freezing temperatures of the solid machinery below and increasing the energy barrier required for ice to form. Any droplets that do freeze are quickly melted through heat from the CNTs.
The rough and valley-like texture forces light to bounce continuously between the pillars, maximising energy absorption. This localised heat is channelled directly to the exact points where the ice touches the pillar tips. Instead of melting the entire ice block, the heat rapidly melts just the microscopic base. This creates a thin and lubricating layer of liquid water and trapped air, reducing adhesion and allowing the remaining solid ice structure to simply slide off under its own weight or a gentle breeze.
The team explains that the film contains '40.8% carbon, 28.5% oxygen and 30.7% silicon' in the paper Laser-induced hierarchical micro/nanostructures on flexible CNT-silicone film for synergistic passive/active anti/de-icing in extremely low-temperature environments.
Publishing in the International Journal of Extreme Manufacturing, the scientists demonstrate that the film 'exhibits an ultra-high optical absorbance of 98.86% and a photothermal conversion efficiency of 89.3%'. Under simulated 100% sunlight, the material is said to reach a 'surface temperature of 143.2°C within 360s'.
The surface is found to delay freezing of water droplets for 720s when tested in chambers mimicking heavy cloud cover or polar twilight conditions at -50°C and with 20% sunlight. It also reportedly melts a solid frost layer in 840s at 70% sunlight.
The highly elastic silicone matrix can also stretch to 200% of its original length, and is reportedly able to survive repeated bending, harsh sand abrasion, tape peeling and acid exposure without losing its superhydrophobic or thermal properties.
The team explains how conventional solutions, such as chemical de-icers or energy-intensive and embedded electric heaters, can be harmful to the environment. Meanwhile, passive superhydrophobic coatings often fail under high humidity or extremely cold temperatures, and active solar-heating coatings are typically built on rigid substrates that cannot wrap around curved industrial parts and struggle to generate heat in weak sunlight.
In comparison, this prototype de-icing film is said to be non-toxic, does not require any energy input, and withstands humidity and extreme temperatures. It is also flexible enough to wrap around curved wind turbine blades, high-tension power lines and aerospace components, as well as working under weak sunlight.
The researchers are now looking to scale up the laser production process and assess the material’s long-term endurance under realistic and unpredictable outdoor conditions.
Extracted from IOM3 website, read more here