Application examples

Material analysis of PFAS and polysiloxanes

Precise material testing of polymer-based lubricants

Today’s material analysis enables the precise analysis of many substances. As a result, even complex compounds such as polymer-based lubricants can be analyzed. Polymer-based substances are better known as per- and polyfluorinated alkyl substances (PFAS) and polydimethylsiloxanes (PDMS). Polymer-based compounds are widely used in industry – and are even indispensable for some industries. They are often used as contact protection oils. The reasons for this are their unique physical and chemical properties. Perfluorinated polyethers (PFPE), substances from the PFAS group, are chemically resistant, have a low surface tension and are thermostable. PDMS is used due to its thermostable properties, low coefficient of friction and low surface energy, which is why it is often used as a release agent.

Industries

Electronics industry
Automotive industry
Medical industry
Food industry
Aviation and aerospace technology
Processing industry
Glass industry (optics)

Typical application

Contact protection oil on relays, plug contacts,
electric motors and slip rings
Protection against moisture, oxidation (corrosion) and dust
Contact protection oil on sensors and plug contacts
Protection against moisture and oxidation (corrosion)
Lubricant (protective film) for prostheses and implants
Reduction of friction
Release agent for plasters
Non-stick coatings
Coatings, lubricants, protective oils
Stability against extreme state variables (temperatures, pressures, …)
Sealants and lubricants in reactors
Chemical stability against corrosive environments
Protective film (anti-scratch coating)
Hydrophobic coating (lotus effect)

In the course of the current discussions about the ban on PFAS, as well as the sustainable and environmentally friendly use of chemicals, there is an increasing need for for detailed information on these contact protection oils. But also for detailed information about the chemical composition of polymer-based contact chemical composition of the polymer-based contact protection oils is also required in order to determine the cause of the failure. TOF-SIMS technology, a highly sensitive mass spectrometry, offers an effective and fast way of analyzing materials. possibility of material analysis.

Material analyses for the structural elucidation of PFPE and polysiloxanes using the TOF-SIMS method

In the field of technical components such as slip rings or electric motors PFAS – specifically perfluorinated polyethers (PFPE) – are often used as contact protection agents. used as contact protection agents. However, PFPE merely refers to the substance group. Within a large number of contact protection oils exist within this group. They differ in their additives (for the characterization of additives see Application example “Material analysis of lubricants: Application examples – Detection and exact identification of lubricant coatings using TOF-SIMS”) but also in their molecular structure. As with other polymers, they can be different repeating units and different molecular weight distributions. molecular weight distributions. These factors have a major influence influence on the physical and chemical properties of the contact protection oil. In safety data sheets usually only contain information on the chemical composition chemical composition, such as perfluorinated polyethers (PFPE). (PFPE) are given. Details on the specific chemistry are rarely published due to rarely published due to company secrets.

Using the TOF-SIMS method and special sample preparation, both the chemistry the chemistry, the repeat units and the molecular weight distribution of the polymeric base polymer base oils can be characterized.

Results: TOF-SIMS analysis of polymer-based lubricants

The analysis of lubricants using the TOF-SIMS method provides detailed information about their chemical composition. In addition, impurities, foreign contamination and also chemical-physical changes due to degradation can be identified.

Case study 1: Characterization of the repeat unit and molecular weight of a PFPEs

This example deals with the material analysis of a PFPE oil. After
special sample preparation, the PFPE can be analyzed directly.

The peak patterns (R) in the section of the mass spectrometric spectrum of the
negative secondary ions indicate a perfluorinated polyether with a repeat unit of
a repeat unit of 166 u. The contact protection oil can be clearly assigned to a
PFPE oil of the Krytox® family.

The section of the TOF-SIMS spectrum of the positive secondary ions shows the molecular weight distribution of the contact protection oil is shown.

With the help of the information obtained from the material analyses about the chemical composition of the polymer-based protective oils such as PDMS and PFAS (such as such as PFPE) can be clearly identified.

Case study 2: Comparative material analyses of PFPE contact protection oils

As a service provider in material and damage analysis, we often find that the use of supposedly identical contact protection oils can lead to considerable damage. can lead to considerable damage. Differences in the end and side groups as well as in the molecular weight distribution influence the chemical-physical properties of the contact properties of the contact protection oil. Therefore, in practice, the oils are often components with product references (e.g. the contact protection oil recommended by the recommended contact protection oil).

The diagram above shows the results of the analysis of a case of damage. The background to the investigation was the failure of technical components (electric motors and grinding tracks). In the first example identical repeat unit could be identified in both PFPEs. Differences became apparent in the molecular weight of the contact protection oils. While the reference had an average molecular weight of 3400 u, the molecular weight of the molecular weight of the component sample was 2300 u. As the molecular weight is strongly with the viscosity of the lubricant, it is likely that the incorrectly PFPE (lower viscosity) is responsible for the failure.

In the further example, the comparison revealed the use of an incorrect PFPE type. While the reference and the first component used a PFPE of the same type Fomblin® as well as a very similar molecular weight distribution (2500 u), the material analysis of the other components revealed a completely different PFPE. different PFPE. Here the analysis revealed that it was the PFPE type Demnum® with with an average molecular weight of around 3900 u. The result is increased wear due to insufficient lubrication performance.

Case study 3: Material analysis of polysiloxane-based medical coatings

The last case study deals with the examination of a polysiloxane coating (PDMS) on medical syringes. medical syringes. The background to the investigation was the precise determination of the PDMS coating of the needles. This is because the information obtained is important for the assessment in the context of functionality and patient safety. Medical companies must ensure that the materials used (in this case PDMS) are biocompatible. In addition, the substances must not have any toxicological properties that could cause health problems. In addition, the sliding properties depend heavily on the average molecular molecular weight of the PDMS used.

Material analysis using TOF-SIMS made it possible to precisely characterize the PDMS coating. The results show that it is a low molecular weight CH₃-terminated PDMS with an average molecular weight of 2000 u. The CH₃ end groups ensure that no reactions occur in the body (e.g. reaction with water). It is therefore non-toxic to the human organism.

Summary: Damage and material analysis of PFAS/PFPE and polysiloxanes

The analysis of polymer-based lubricants such as PFPE and polysiloxanes (PDMS) is highly relevant for industry and medicine. Due to their chemical and physical properties such as chemical resistance, low friction and temperature stability, they are used everywhere. However, their properties differ greatly depending on their molecular structure, molecular weight distribution and additives. Practical experience shows that PFPE and polysiloxane (PDMS) lubricants that appear to be the same have differences in their chemical composition and structure. structure. Using the wrong lubricants can, for example, lead to increased wear, deposits on electrical contacts and neighboring components, which can ultimately lead to functional failures and costly repairs. The TOF-SIMS technology offers an efficient method for material and damage analysis of polymer-based lubricants such as PFPE or PDMS. The high sensitivity enables:

Exact material analysis: precise characterization of base oils, additives, repeat units and molecular weight distributions of polymer-based lubricants
Flexible sampling: non-destructive sampling, can also be carried out on site

Contact us to find out more about our material and damage analyses in the field of polymer-based lubricants. We are happy to support you with questions from industry and medicine.

Publications

¹Kontaktschutzöl auf Schleifringüberträgern (Teil 2).
H.Feld, N. Oberender, J. Hellwig: Oberflächen Polysurfaces, 4 (2022) 18 – 20.

²Secondary Ion Emission from Perfluorinated Polyethers under MeV- and keV-Ion Bombardment.
H. Feld, A. Leute, D. Rading, and A. Benninghoven; M. P. Chiarelli and D. M. Hercules: Analytical Chemistry, 65 (1993) 1947 – 1953.
DOI: https://doi.org/10.1021/ac00063a005