The usability of a contact lens largely depends on its design. Contact lenses need to be safe and convenient as they are in close contact with the eye and people may use them for extended periods of time.
Different types of surface treatments have been used to improve the surface properties of contact lenses so that they have a better hydrophilic surface with improved scratch and deposit resistance. Therefore, it is crucial to characterize the surface of a contact lens in order to optimize its design.
Figure 1. Contact lens
The elemental and chemical composition of the contact lens surface can be efficiently analyzed using X-ray Photoelectron Spectroscopy (XPS) . The interfacial chemistry and useful data about the coating layers, such as thickness and uniformity of the coating, can also be obtained with XPS.
When coupled to automated processing, XPS can be utilized to analyze the coating thickness for an assortment of lenses. This article discusses the analysis of a set of contact lens samples to determine their elemental and chemical composition using a Thermo Scientific K-Alpha XPS (Figure 2).
Figure 2. The Thermo Scientific K-Alpha XPS
Experimental and Results
The experiment used the K-Alpha XPS to analyze a set of contact lens samples. The analysis conditions were maintained stable during the analysis with the help of the simple turn-key charge compensation system of the K-Alpha. The survey scan spectra of the two lenses are illustrated in Figure 3.
The elemental composition of the lens surface can be quantitatively characterized with the wide scan survey spectrum, a narrow scan region spectrum enables investigating the chemical composition of the lens surface.
Figure 3. Survey spectra of two contact lenses
This data enables identifying a contamination source or corroborating the success of the treatments or additives applied on the lens. The carbon chemical states determined at the lens surface are depicted in Figure 4. A depth profile of a contact lens is illustrated in Figure 5.
Low energy argon ions are used for the contact lens profiling, with the coating layer highlighted with gray. By maintaining the chemical integrity of the sample, its chemical changes are observed as a function of depth. K-Alpha uses low energy ion beam for maintaining the polymer chemistry even while performing profiling.
Figure 4. The chemical states of carbon detected at the surface of a contact lens
Figure 5. A depth profile of a contact lens using 200 eV argon ions. The coating layer has been highlighted in grey.
Experiment Recipe and Batch Processing
K-Alpha enables developing expertly designed experimental recipes to be utilized by several users. This capability is especially helpful in the analysis of large sets of samples multiple times in order to acquire the same information. Selecting the required recipe and defining the sample analysis positions are the actions that need to be done by the users.
The processes of data acquisition through processing can be carried out efficiently with the Avantage Data System, which enables exporting a series of analyses to a spreadsheet and batch processing of sample sets. Figures 6 and 7 present an example of the experiment recipe, showing the output after the automated processing.
Figure 6. An example of an experiment recipe for batch processing
Figure 7. An example of batch processing output for a set of contact lenses
The results clearly demonstrate the ability of the K-Alpha equipped with the Avantage Data System to perform routine characterization of large sample sets of contact lenses in order to determine their surface’s elemental and chemical composition. The composition and uniformity of the coating layer can be determined with the help of depth profiling.
This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.
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