Polymer Design - Using SEM to Optimize Polymer Properties

Polymers are used in a number of applications: engineered combinations of monomers create a nearly infinite number of molecules with different properties, which are identified by the structure and chemical composition of the molecule.

The form of the molecule greatly influences the behavior of the polymer when subjected to different external forces. This article provides practical examples of how scanning electron microscopes (SEMs) can deliver surprising results.

Polymers: Ideal Crafting Materials

This article first focuses on what kind of information SEMs provide on thermoplastic polymers. Thermoplastic polymers have an extremely linear chemical structure and weak interactions binding the molecules together. In these polymers, the bonds are easily broken when the polymer is heated, leading to material deformation. In addition to having a good resistance to high temperatures, they are also characterized by an impressive resistance to abrasion and high chemical inertia.

Thermosplastic polymers can be used in different types of industrial processes, such as extrusion or printing, making them the ideal crafting materials for items with the most intricate shapes.

Figure 1. A SEM image of a meltblown fiber. The diameter of the fiber can easily be measured at this magnification.

Thermoplastic polymers are extensively used in the production of fibers, packaging films, and electronic and electrical parts. They are also used to make daily use items, such as oven-proof kitchenware. Using SEMs, not only the quality and properties of these polymers can be studied, but also the processes can be improved and the impact of different forces on these material can be explored.

What Does a SEM Tell Me About My Polymer?

After an abrasion test, the surface of the polymer, when looked at carefully, can reveal the real consequences of the stress applied to the material, thus allowing for further development of the material or for quality controls at the final stages of the production chain.

Here, the remarkable techniques are roughness analysis through stereoscopic reconstructions or shape from shading, which allow Scientists to determine the depth of the scratches on the material.

Figure 2. A SEM image of a wax. SEM with EDS analysis was used to investigate the distribution and composition of particles dispersed in the polymeric matrix.

Figure 3. A semiconductor imaged with a SEM can be easily inspected to find defects in the production process.

Diameters of particles and fibers can be very accurately measured on a picture taken at high magnification. Different kinds of information, ranging from fluidynamic properties, to the maximum particle size that can be caught in a filter, to how well a powder can be dispersed in a solution can be obtained from these results.

There are also automated procedures available to instruct SEMs to autonomously capture pictures of the sample and determine important parameters like areas, aspect ratios, axis size or diameter. These results offer a large amount of data easily and rapidly, saving valuable time to Researchers so that they can invest their time in a more useful and effective way.

SEMs can also be employed to explore new and trending manufacturing processes like 3D printing, where a polymer is extruded and manipulated to build a real life version of a digital 3D drawing. The quality and resolution of the print, as well as the components of the printer itself, can be measured and studied to significantly enhance the performance of the device.

Figure 4. A SEM image of a 3D printed rabbit. SEM was used to investigate the object for defects.

When particle distribution in a film is analyzed, having knowledge about the composition of the different phases can help enhance the dispersion process. This analysis can be easily carried out using energy dispersive X-ray spectroscopy (EDX or EDS) - the predominantly used microanalysis method available on SEMs. The chemical composition of the analyzed sample is displayed on the screen within a couple of seconds.

Can I Load My Polymer in a SEM?

A number of issues arise while analyzing a polymer with an electron microscope. However, as the polymer industry is one of the largest players among SEM users, a variety of simple solutions are available to achieve the desired results.

For instance, SEMs image electrons on the sample at an extremely high voltage. Conversely, the current intensity is extremely small to avoid any damage caused to the sample. In addition, the observed sample has to be placed in a confined environment, in high vacuum. This can result in multiple consequences for the material, based on its physical and chemical resistance.

Accumulation of electrons on the surface of the sample, also called the charging effect, is one of the major concerns. This problem can be avoided by creating a conductive bridge linking the material surface to a part of the device kept at ground potential.

Changing the vacuum level in the microscope in accordance with the material specifications is an easier alternative, which will result in a massive discharging of the sample.

The last option is a sputter coating device that can coat the material with a thin layer of conductive materials such as gold. This will make it ideal for SEM analysis without significantly changing the sample structure.

Polymers are usually extremely sensitive materials. They can be damaged by an electron beam, particularly when a very high voltage is applied. The electron emitted by the microscope can interact with the weak inter-molecular bonds and break them.

Some SEMs provide a low emission current option that makes it possible to image the sample without damaging it.

SABIC, which is a key player in the polymers market, already employs SEM to enhance its products. The company operates at multiple levels on the most advanced and sophisticated techniques in polymers production.

This information has been sourced, reviewed and adapted from materials provided by Phenom-World BV.

For more information on this source, please visit Phenom-World BV.

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