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XPS Analysis of Polymer Blends 

 

C 1s region

 

Introduction


 
The following XPS results demonstrate the application of the Kratos AXIS HSi XPS for the analysis of polymer blends. The polymer films were prepared by allowing a 50/50 2% solution of PMMA/PVC in THF to air dry on a watch glass. Features such as imaging XPS, small area multi-point spectroscopy and simple to use yet highly efficient charge neutralisation show why the Kratos AXIS HSi is ideal for polymer and insulating material analysis. These features greatly expand the range of applications for an instrument designed to provide research quality data in a simple to use and highly affordable manner.
O 1s region
Cl 2p region
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Figure 1: XPS spectra from a PMMA and PVC polymer blend
      a) C 1s region
      b) O 1s region
      c) Cl  2p region

 

 

High Resolution XPS of Polymer Blends


 
The most important aspect of XPS for polymer analysis using the Kratos AXIS HSi is the ease and efficiency of charge neutralisation. Only the best energy resolution can be obtained from polymer surfaces when XPS measurements are made from a sample with a uniform potential within and across the sample surface. The patented charge neutralisation system of the AXIS HSi is the most effective and easy to use system available for analysis of insulating materials.
The high resolution C 1s, O 1s and Cl 2p spectra acquired from an area of 350 x 700 µm, shown in Figures 1a - 1c, demonstrate the ability to obtain excellent energy resolution from polymer blends of PMMA and PVC. XPS analysis performed using the AXIS HSi provides chemical state information with quality unachievable from other XPS instrumentation. For example, the O 1s peak shape clearly distinguishes the two chemical environments of O present in PMMA as well as a minor component resulting from SiOx contamination. Furthermore, the high energy resolution allows unambiguous curve fitting of the C 1s region to determine the amounts of PMMA and PVC present at the surface of the film.
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XPS Images from blend
 
 
Figure 2: XPS images from polymer blend
      a) chlorine distribution
      b) oxygen distribution
      c) overlay showing blend composition

 

XPS Imaging of Polymer Blends


 
Many polymer blends are immiscible when cast from solution and allowed to air dry. Polymer films consisting of PMMA and PVC cast from THF solutions are excellent examples, and imaging XPS can provide valuable information about the degree of phase segregation across the surface of these films. The easy to use charge neutraliser in combination with the imaging capability of the Kratos AXIS HSi make it ideal for polymer film analysis. XPS images acquired using the Kratos AXIS HSi show the Cl and O distributions (Figures 2a and 2b) associated with the PVC and PMMA components respectively. The coloured overlay in Figure 2c shows the complementary nature of the components of the blend. Phase segregated features of less than 30µm can be identified in short times due the excellent collection efficiency of the magnetic immersion lens. The high collection efficiency allows for fast image acquisition with relatively low x-ray flux density, which is important to avoid sample degradation across the surface of polymers, which will occur from highly focussed x-ray beams.
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High Resolution Multipoint Spectra
 
Figure 3: C 1s multipoint spectra from polymer blend
      (a) from area of high chlorine intensity, and
      (b) from low chlorine intensity area.

 

 

Multi-Point Spectroscopy


 
Small area spectroscopy can be performed from various areas of interest within an XPS image using one of several spot sizes available on the AXIS HSi. Because the imaging is performed by rastering a virtual spot across the surface of a stationary sample using electrostatic deflection plates, the area of analysis can be defined with complete confidence. Any number of positions can be analysed during an experiment, and recalled at a later time to perform further analysis at the exact location if desired.
The two C 1s spectra in Figures 3a and 3b were collected from areas with high and low Cl intensity (labelled as Pt1 and Pt2 in Figure 2c) across the surface of the polymer blend respectively. The area of low Cl intensity shows a C 1s peak shape indicative of pure PMMA, while the area of high Cl intensity shows a significant amount of PMMA in the PVC enriched area. This work supports the idea of areas containing only PMMA as well as a PMMA overlayer covering the PVC enriched areas of the polymer film.
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Summary


 
The AXIS HSi is a high quality research grade electron spectrometer, the coaxial magnetic lens and charge neutralisation system are particularly suited to the analysis of insulating materials and inhomogeneous polymers in particular as demonstrated in this case.

The key features of the AXIS HSi demonstrated are:

  • Excellent spectral resolution
  • Uniform charge compensation
  • XPS imaging
  • High quality small spot spectroscopy

 

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Last Update: 99/03/07

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