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Measuring treatment, Part 4
February 15, 2008
In Part 3, I discussed the use of XPS to determine the atomic composition of a substrate surface and in particular the surface oxygen concentration. We have also discussed in Part 1, the use of treatment solutions to determine surface tension or dyne level of the surface. Combining the measurements we are able to plot the surface treatment versus the surface oxygen composition. These curves are very instructive in that they help to determine the difference in the effect of a treatment method on the substrate surface. Figure 1 is a schematic plot the two treatment vs. surface oxygen curves for both flame and corona treatment of a homopolymer polypropylene surface, a notoriously difficult polymer to treat .
Figure 1: Plot of dyne level vs. % surface oxygen concentration
What we see in the figure is that a flame treater gives a higher dyne level at a lower oxygen level. i.e. it is easier to get a higher treatment value for PP with the flame treater than the corona. Why is this separation of the curves happening for the polypropylene?
This can be answered by looking in more detail into the surface chemistry generated by the different treatment technologies and this can be done with the XPS spectra. Figure 2 is a representative low resolution XPS spectra showing peaks for carbon and oxygen.
Figure 2: Low resolution XPS spectra
The relative intensities of these peaks are what is used to determine the relative atomic concentrations of the surface. To determine the actual composition of the surface, a high-resolution spectra is required. One such high resolution spectra is shown in Figure 3.
Figure 3: High-resolution carbon XPS spectra showing positions of various carbon-oxygen functionalities
Data from spectra such as Figure 3 allow the estimation of the relative amounts of the three carbon-oxygen functions.
When studies like this are undertaken what we find is that flame treaters generate a higher concentration of the lower oxidation state alcohol groups on the surface while corona treaters generate higher oxidation state carbon oxygen groups such as the carbonyl and acid groups. This difference is apparently what is driving the higher dyne levels of the flame-treated samples relative to the corona-treated surface.
Studies of this nature are the best way to determine the real effect of a treatment method on a particular surface.
Posted by Eldridge M. Mount on February 15, 2008 | Comments (0)