Part II: The influence of substrate type, film thickness, and primary ion type on molecular weight characterization of linear polydimethyl siloxane films by secondary ion mass spectrometry

Abstract

In our previous paper, we showed that the molecular weight of linear, trimethyl‐terminated polydimethyl siloxane (PDMS) can be estimated using a standard curve by measuring PDMS endgroup‐related signal normalized to backbone‐related signal for PDMS films that are thick relative to the information depth of SIMS. Within industrial surface analysis laboratories, it is more likely that PDMS fluid is encountered as a thin film, perhaps as a contaminant or an additive that has exuded from a bulk material. This paper explores the influence of PDMS film thickness, substrate type, and primary ion projectile type (cluster vs. monoatomic) on the ratio of measured endgroup:backbone peak area ratio. These factors are shown to have a significant influence on the measured spectra, and these effects should be carefully considered before making molecular weight estimates of PDMS based on SIMS peak ratios.