Engineers have long grappled with the challenges posed by vibrations and noise in technical applications. Damping materials such as foams, rubber, and mechanical elements like springs and shock absorbers have been used to mitigate these issues, but they often come with drawbacks such as increased bulk, weight, and cost. Additionally, retrofitting damping elements may not always effectively suppress vibrations.
To address these challenges, there is a growing global demand for materials that possess both rigidity and effective internal damping capabilities. However, achieving this balance is no easy task, as these properties are typically considered to be mutually exclusive.
In response to this demand, ETH materials researchers have made a significant breakthrough by developing a material that successfully combines these seemingly incompatible properties. Ioanna Tsimouri, with the assistance of professors Andrei Gusev and Walter Caseri, has created materials consisting of layers of stiff materials connected by ultra-thin rubber-like layers formed by crosslinking a polydimethylsiloxane (PDMS) mixture. This innovation holds great promise for addressing the challenges associated with vibrations and noise in various technical applications.
The initial prototypes utilized silicon and glass plates with a thickness of 0.2–0.3 mm, interconnected by thin rubber-like layers measuring only a few hundred nanometers. Through rigorous testing, these novel composite materials have demonstrated the desired properties as anticipated by the researchers. Collaborating with materials physicist Gusev, the researcher initially employed computer simulations to determine the optimal thickness of the connecting rubber-like layers for achieving high stiffness and damping of the composite material.
The simulations indicated that the layer thickness must adhere to a specific ratio to exhibit the desired material properties. According to these calculations, the damping polymer layers should constitute less than 1 percent of the total material volume, while the rigid glass or silicon layers must represent at least 99 percent.
“There is very little of a damping effect if the polymer layer is too thin. If it is too thick, the material is not stiff enough,” Tsimouri explains.
In the next phase, she and Caseri conducted experimental verifications of the calculations and developed various versions of the composite material in the lab.
The rigid layers of the material Tsimouri utilized included smartphone-grade glass. The polymer was created by blending commercially available PDMS-based polymers containing chemically reactive sites. Upon adding a catalyst, these sites combined to form a polymer network, creating a rubber-like polymer that links the stiff plates akin to a two-component sealant.
With the assistance of UK collaborator Peter Hine, the materials researcher proceeded to evaluate the frequency- and temperature-dependent mechanical properties of the layered materials (laminates) using a three-point bending test. In addition, she conducted a straightforward yet meaningful practical test: dropping the laminate plates from a height of 25 centimeters onto a table and comparing the acoustic and mechanical damping with that of a plate of the same size made of pure glass.
The laminate exhibited excellent damping properties and stability. It produced a much quieter impact on the table and did not bounce, unlike the pure glass, which made a loud crash, bounced, and flipped over.
“Using this test, I was able to show that the laminate is excellent at damping vibrations and noise,” says Tsimouri. “After finding a mixture of PDMS polymers that results in a rubber-like polymer with enhanced damping performance over a broad range of temperatures, the next biggest difficulty was creating the rubber-like layer in the desired thickness.”
The rapid reaction of the polymers to the catalyst required the development of a specialized process for applying the solutions to glass or silicon discs. Extensive time was also dedicated to ensuring the thickness of the layers, involving the production of cross-sections of the laminate and examination under a scanning electron microscope.
The potential applications for the laminate are vast, ranging from window glass and machine housing to car parts, as well as in aerospace and sensor technology where advanced damping materials are highly sought after. The researchers emphasize the immense global market for damping materials.
Additionally, the polymer’s temperature-resistant properties allow it to withstand a wide range of temperatures without compromising its damping capabilities, except below a temperature of minus 125 degrees Celsius, where it becomes glassy and loses its damping capacity.
Furthermore, the sustainability and resource conservation aspects of the laminate are noteworthy, as both glass and silicon are easily recyclable, with the polymer decomposing to glass when melted down, thus not affecting the recycling process.
Caseri believes the technology is easily scalable. “Manufacturers with the right machines can also produce the laminate in panels of dimensions of several square meters. The manufacturing process is not that complicated.”
Journal reference:
- Ioanna Ch. Tsimouri, Walter Caseri, Peter J. Hine, Andrei A. Gusev. Lightweight silicon and glass composites with submicron viscoelastic interlayers and unconventional combinations of stiffness and damping. Composites Part B: Engineering, 2024; DOI: 10.1016/j.compositesb.2024.111717
