Case Study: TEM Analysis of Polymer Rubber Blend Using Cryo-Ultramicrotomy and Osmium Staining

Post by: Rich Brown (retired) MVA Scientific Consultants and Matthew Muller, Research Scientist, MVA Scientific Consultants

Introduction
This is a summary as to how MVA Scientific Consultants prepares polymer rubber blend plastics such as high impact polystyrene (HIPS) for transmission electron microscopy (TEM) analysis. HIPS is a polystyrene polymer whose impact strength has been elevated by the incorporation of rubber particles. As modified polystyrene, HIPS contains rubber components (typically polybutadiene) for better durability, flexibility, processing, and other desired characteristics. The size and distribution of the rubber inclusions are of interest when evaluating this type of polymer blend. Through cryo-ultramicrotomy and heavy metal staining, MVA can image the rubber inclusions with excellent contrast at high magnifications using high resolution TEM imaging.

Methods
Cryo-ultramicrotomy is performed after a face is trimmed on the sample. The microtome used has a cryo stage, and cutting of thin sections is achieved by cooling the sample and diamond knife to cryogenic conditions that will provide 70 nanometer thin sections. The thin sections are captured and transferred to a copper mesh TEM grid.

The thin sections are exposed to osmium vapors that selectively stain the rubber inclusions providing contrast when imaged using a TEM. Once stained the thin sections are ready for TEM imaging (figures shown below).

Figure 1 – TEM analysis image of the polymer blend-HIPS thin section, osmium stained; Rubber appears as darker phase.

Figure 2 – TEM analysis image of the polymer blend-HIPS thin section, osmium stained.

In copolymer blends, phase separation has a significant impact on the physical properties of the material. High resolution TEM imaging of the stained copolymers can reveal the domain type and size in the processed material.