How engineers and researchers can boost polymers properties with SEM
Polymers have many uses and applications: engineered combinations of monomers produce a nearly infinite number of molecules with different properties, which are determined by the chemical composition and structure of the molecule. The form of the molecule has a big influence on how the polymer will behave when exposed to different external forces. In this blog, you’ll find practical examples of how Scanning Electron Microscopes (SEMs) can provide unexpected results.
Polymers: ideal crafting materials
First, I’ll focus on what kind of information SEMs provide on thermoplastic polymers.
These materials have a very linear chemical structure and weak interactions binding the molecules together. In these polymers, the bonds are easily broken when the polymer is heated up, which results in the material deforming. They have an good resistance to high temperatures, and are also characterized by a high chemical inertia and impressive resistance to abrasion.
Thermosplastic polymers can undergo different kinds of industrial processes, such as printing or extrusion, making them the perfect crafting materials for items with the most complex of shapes.
Fig. 1: A SEM image of a meltblown fiber. The diameter of the fiber can easily be measured at this magnification.
To give a few examples of their applications, thermoplastic polymers are widely used in the production of fibers, electrical and electronic parts, packaging films, but also for daily use items, such as oven-proof kitchenware. SEMs can be used to investigate their properties and quality, but also to improve the processes and investigate how different forces affect these materials.
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What does a SEM tell me about my polymer?
After an abrasion test, a close look at the surface of the polymer can show the real consequences of the stress applied to the material. This allows for further development of the material or for quality controls at the end of the production chain.
In this case, the interesting techniques are roughness analysis via stereoscopic reconstructions or shape from shading, which enable researchers to measure the depth of the scratches on the material.
Fig 2.: A SEM image of a wax. SEM with EDS analysis Fig 3.: A semiconductor imaged with a SEM can be
was used to investigate the distribution and easily inspected to find defects in the production
composition of particles dispersed in the polymeric process.
matrix.
Diameters of fibers and particles can be measured very accurately on a picture taken at high magnification. These can provide different kind of information, 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.
Automated procedures are also available to instruct SEMs to autonomously collect pictures of the sample and measure important parameters like diameter, axis size, aspect ratios or areas. These results provide a huge amount of data easily and quickly, saving valuable time that researchers can invest in a more productive and efficient way.
SEMs can also be used to investigate new and trending manufacturing processes like 3D printing, where a polymer is extruded and manipulated to create a real life version of a digital 3D drawing. The resolution and quality of the print, as well as the components of the printer itself, can be measured and investigated to dramatically boost the performance of the device.
Fig 4.: A SEM image of a 3D-printed rabbit. SEM was used to investigate the object for defects.
When analysing the distribution of particles in a film, knowing the composition of the different phases can help improve the dispersion process. This analysis can be easily performed using energy dispersive x-ray spectroscopy (EDX or EDS) - the most used microanalysis technique available on SEMs. In a couple of seconds, the chemical composition of the analysed sample is displayed on screen.
Can I load my polymer in a SEM?
Analysing a polymer with an electron microscope raises different problems. But as the polymer industry is one of the biggest players among SEM users, a number of simple solutions are available to obtain the desired results.
For example, SEMs image electrons on the sample at a very high voltage. On the other hand, the current intensity is very small to avoid damage to the sample. On top of that, the observed sample has to be in a confined environment, in high vacuum. This can lead to several consequences for the material, depending on its chemical and physical resistance.
The main problem is the accumulation of electrons on the surface of the sample, also known as the charging effect. This issue can be avoided by creating a conductive bridge linking the surface of the material to a part of the device which is at ground potential.
An easier alternative is to change the vacuum level in the microscope according to the material specifications, which will lead to a massive discharging of the sample.
The final option is a sputter coating device that can cover the material with a thin layer of gold or other conductive material. This will make it suitable for SEM analysis without meaningfully altering the structure of the sample.
Polymers are generally very sensitive materials. The electron beam can damage them, especially when a very high voltage is applied. The electron emitted by the microscope can, in fact, interact with the delicate 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.
A company that already uses SEM to improve its products is SABIC, a main player in the polymers market. SABIC operates at several levels on the most sophisticated and advanced techniques in polymers production. Download this free document to have a sneak peak on how this company is using electron microscopy to generate results on a daily basis.
