Our last article discussed the polymer and technology involved in making contact lenses and how good lens design is all about the surface of the lens.
We analyzed a set of contact lens samples with X-ray Photoelectron Spectroscopy (XPS). XPS is an ideal analytical method for investigating elemental and chemical composition of the surface. It can also provide information about the coating layers (coating uniformity and thickness) and the interfacial chemistry. In conjunction with automated processing, it can be used to investigate coating thickness across a group of lenses.
Below are the survey scan spectra of two lenses. The wide scan survey spectrum allows quantitative elemental characterization of the surface.
Contact lenses are subjected to different kinds of surface treatments with the intent to make the surfaces more hydrophilic, deposit resistant, or scratch resistant. The chemical state of the element can be studied by a narrow scan region spectrum. With this information, it is possible to confirm the treatments or additives used on the lens have been successful, or identify a source of contamination.
With XPS we could see the depth profile of the contact lens. The contact lens was profiled using low energy argon ions. The coating layer was highlighted with gray. The chemical integrity of the sample was maintained and chemical changes could be traced as a function of depth. Using low energy ion beam the instrument was able to maintain the polymer chemistry even during profiling.
In addition, we were able to analyze large sets of samples several times for certain ‘recipes’ that were developed. The results of the analyses could then be exported to a spreadsheet and batch processed.
Read Analyzing Contact Lens Samples to see the chemical states of carbon detected at the surface of the contact lens, a depth profile of the contact lens using 200 eV argon ions, an example of an experiment recipe for batch processing, and a chart of the batch processing output results of the experiment using the XPS instrument to analyze the elemental and chemical composition of a set of contact lens samples.