Ultra-thin Interlayers Strengthen Flexible Composite Materials

Researchers at Empa have developed an ultra-thin intermediate layer that significantly improves the mechanical resistance of aluminium-coated polymer films used in satellite insulation. The innovation enhances crack resistance and flexibility under extreme temperature fluctuations and could also benefit flexible electronics, smart textiles and medical sensor technologies.

Aluminium-coated polymer films – known as multilayer insulation (MLI) or superinsulation – play a crucial role in protecting satellites and space probes from extreme temperature variations. In low Earth orbit, temperature differences between sunlit and shaded sides can reach around 200 degrees Celsius, occurring up to 16 times per day.

To withstand these conditions, a highly resistant polymer such as polyimide is typically coated with a thin aluminium layer. The material is also used in applications on Earth, including emergency blankets. However, its long-term durability under mechanical and thermal stress remains a key research focus.

At Empa's Laboratory for Mechanics of Materials and Nanostructures in Thun, researchers led by Barbara Putz have investigated the nanoscale interface between polymer and metal. During conventional coating processes, a naturally forming intermediate layer – only a few nanometres thick – improves adhesion between polyimide and aluminium.

To better understand and optimise this interface, the researchers created a defined model system: a 50-micrometre polyimide film coated with 150 nanometres of aluminium and an additional five-nanometre aluminium oxide interlayer.

Using a specialised vacuum coating system from the Empa spin-off Swiss Cluster AG, different coating steps can be applied without removing the sample from the vacuum chamber. This ensures clean interfaces and precise thickness control.

Mechanical testing and temperature shock experiments showed that the engineered interlayer significantly increases elasticity and improves resistance to cracks and delamination. The team now plans to vary interlayer thickness and apply the concept to other polymer substrates.

The technology is directly relevant to space applications such as ESA's BepiColombo mission and NASA's James Webb Space Telescope, whose sunshield relies on similar multilayer systems. These materials must withstand folding during transport, deployment in orbit and potential damage from space debris.

Beyond aerospace, the research opens up opportunities in flexible electronics, where metal-coated polymer substrates are widely used. Targeted interlayers could improve the mechanical durability of multilayer thin films in:

• Foldable and rollable electronic devices
• Smart textiles
• Flexible medical sensors

By combining materials science, nanotechnology and advanced coating processes, the research contributes to the development of more robust lightweight composites for both space and terrestrial applications.

Barbara Putz has received an Ambizione Grant from the Swiss National Science Foundation (SNSF) to further advance the project.