Heterogenous polymeric nanoparticles have been widely applied in many areas, including pharmaceutical, electronics, food and agriculture industries. The ability to measure the internal chemical distribution in these nanoparticles can significantly support the development and testing of products relevant to these industries. X-ray photoelectron spectroscopy (XPS) provides quantitative chemical information of material surfaces. Argon cluster sputtering is typically used for the controlled removal of superficial layers and exposure of buried material. In this work, we used XPS sputter depth profiling with argon cluster ions to perform chemical depth profiling of polymeric core/shell nanoparticles.<br/>We demonstrate, for the first time, that XPS and time-of-flight secondary ion mass spectrometry (TOF-SIMS) coupled with argon cluster sputtering can be used for chemical depth profiling of heterogenous polymer nanoparticles, providing valuable information on their chemistry and structure. We first carefully investigated the sputtering behaviour of spherical polystyrene nanoparticle using an argon cluster beam and scanning electron microscopy (SEM). Based on these observations, we then developed a geometric model to interpret quantitative chemical depth profiling of nanoparticles using XPS and TOF-SIMS. We successfully applied this model to analyse the structure and chemistry of nonideal poly(tetrafluoroethylene)-poly(methyl methacrylate) (PTFE-PMMA) core/shell particles with an average diameter of approximately 150 nm (Figure 1). The PTFE core of the particles contains the element fluorine that is not present in the PMMA shell, and therefore allows the size and quantity of the core materials to be determined during the analysis. In conclusion, the approach developed here is useful in the analysis of organic multicomponent nanoparticles. It complements microscopic analysis by providing average chemical and structure information across a large particle population.

Argon cluster sputtering reveals the internal chemical distribution in heterogenous polymeric nanoparticles

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