Have you heard the saying that there are three ways to look at anything — your way, my way and the truth? The point of the adage is that things appear different depending on how you look at them. Different perspectives yield different results. Microscopy techniques are like that. When you’re engaging in polymer testing, it’s highly useful to have more than one way to look at a sample, and various microscopy techniques give us enriched perspective.
Different microscopy techniques examine materials in different ways, and each is useful for different reasons. Polymer Solutions scientists commonly use four types of microscopy in their work: atomic force microscopy (AFM), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Here’s a primer on how each works and how we use them:
As its name implies, the atomic force microscopy technique uses the force particles exert on each other at the atomic level to analyze certain aspects of a sample. Although we’re not really “seeing” the detailed information about the sample, how the sample exerts force on the sensing portion of the AFM instrument can give us a picture of the nano-phase morphology or surface roughness of the sample. AFM allows us to work with very small samples — 1cm by 1cm in area or 5mm or less in thickness. This technique is also useful for measuring phase separation and nano-particle dispersion, as well as in surface aging studies.
When you think of microscopy as a visual amplification — viewing something bigger — you’re most closely describing optical microscopy (OM). It’s often the first test scientists turn to when conducting comparative analysis. By magnifying a sample from 10x to more than 100x, we can see many details that aren’t apparent with the naked eye. OM is a good starting point for virtually any kind of sample.
When we need to take an even closer look at a material, we turn to SEM, which can magnify samples
up to 500,000x. An SEM instrument trains a high-energy, focused beam of electrons to examine a sample under vacuum. The electron beam causes the sample to release secondary electrons, which the instrument reads to provide an image. SEM analysis is even more useful when done in conjunction with other testing methods, such as Elemental Dispersion Spectroscopy, which allows us to compare different chemical compositions between layers of a sample. We’ve used SEM analysis to test metals, wood, paint and primer layers, medical devices, food packaging, children’s toys and more.
TEM varies from SEM in that in this test, a beam of electrons passing through a very thin sample yields a wealth of information. The electron density of the sample varies in different areas and interacts with the beam differently, allowing us to create an image that maps the electron density. TEM uses incredibly thin samples — about 0.1 microns in thickness. That’s incredibly small; a single red blood cell is 6 microns thick. We’ve used TEM to test for phase morphology, dispersion of polymer blends, quality control, failure analysis, nanoscale particle incorporation and many more applications.
In the world of polymer testing, there are many, many ways to look at samples. Different types of microscopy give us the tools we need to see things in new and exciting ways.