New Technique Maps Materials at Atomic Level

A new technique developed by a group under the direction of mechanical engineering professor Igor Sokolov utilizes atomic force microscopy alongside machine learning and physical measurements to produce high-resolution maps of materials. The research was published in Materials Today.

Take a photo with a smartphone, and you can notice incredible details—leaves on a tree or strands of hair blowing in the wind. For reference, a strand of hair is about 100,000 nanometers wide. The best traditional light microscopes in laboratories can detect details as small as 200 nanometers, which is about the size of a large virus. The most advanced light microscopes can detect features between 20 and 50 nanometers, roughly the size of a large protein molecule.

Tufts engineers have now developed an imaging technique capable of seeing details as small as 1.6 nanometers, the diameter of a single DNA molecule.

While the upper limit of imaging technology—atomic force microscopy—can detect single atoms, the resulting images are usually rough black-and-white representations, with atoms appearing as bumps on a surface. There is no "color" information to identify specific atoms or materials.

As the tiny atomic force microscope probe scans the surface of a sample, it can identify the types of molecules beneath. For example, if the sample is made up of three different polymers, the system can generate a color map showing the distribution of the molecule types, along with the composite's nanoscale structure, all at a resolution of 1.6 nanometers.

The physical measurements captured include the surface contours, the energy lost by the probe as it separates from the surface, and the length of the "neck" of material that stretches when the probe pulls away.

Using the advanced "ringing mode" of atomic force microscopy, also developed in Sokolov's lab, the system captures twelve distinct physical measurements simultaneously. A machine learning algorithm then processes this wealth of data to generate a detailed profile of the material in the sample.

A Faster Way to Analyze New Materials

The new imaging technology could significantly advance the study of materials with unique mechanical, electrical, or optical properties. Composite polymers, for example, offer a range of desirable qualities, such as superior strength-to-weight ratios, stiffness, flexibility, durability, and heat resistance.

One practical application is in automotive manufacturing, where car bumpers are made from a composite of clay particles and polymers. This innovation has greatly improved the safety, durability, and aesthetics of plastics used in vehicles.

Nanostructure imaging can also help accelerate the development of new products.

Using this technique, we can get a much faster read on a polymer’s qualities. For example, to understand how durable it is, we can expose the polymer to acid, heat, or UV light and then directly image what happens at near-atomic resolution. Because the sensitivity and resolution of this technique is so high, we can see changes long before than any other technique, which might only detect changes at the micrometer scale.

Igor Sokolov, Professor, Tufts University

One potential application of this new imaging technology is in enhancing the environmental sustainability of plastics. By identifying plastic composites that degrade smoothly, layer by layer, it may be possible to prevent the creation of microplastics, which typically result from uneven polymer erosion. Microplastics not only pollute the environment but also enter the food chain and eventually accumulate in human tissue.

The discovery of more resilient plastics that can withstand various conditions could also lead to better, longer-lasting materials, ideal for use in areas such as plumbing and construction.

In healthcare, the technology could be applied to study tooth surfaces, offering insights into how different materials and pathogens erode teeth. This could help in the development of coatings that provide more effective protection.

Sokolov concluded, “Imaging at the nanoscale can help move polymer materials development toward a more analytical approach. Plastics production today is an art based largely on trial and error. You mix polymers that you think might work well together, and you test under conditions that might replicate usage, aging, and environmental exposure, observing mostly macroscopic and microscopic changes in the material. By looking at the nanoscale changes, we can more quickly extrapolate to what might happen to these new materials over time.”

Journal Reference:

Petrov, M. et. al. (2024) Mechanical spectroscopy of materials using atomic force microscopy (AFM-MS). Materials Today. doi.org/10.1016/j.mattod.2024.08.021