Abstract
Surface analysis plays a key role in understanding the function of materials, particularly in biological environments. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) provides highly surface sensitive chemical information that can readily be acquired over large areas and has, thus, become an important surface analysis tool. However, the information‐rich nature of ToF‐SIMS complicates the interpretation and comparison of spectra, particularly in cases where multicomponent samples are being assessed. In this study, a method is presented to assess the chemical variance across 16 poly(meth)acrylates. Materials are selected to contain C6 pendant groups, and ten replicates of each are printed as a polymer microarray. SIMS spectra are acquired for each material with the most intense and unique ions assessed for each material to identify the predominant and distinctive fragmentation pathways within the materials studied. Differentiating acrylate/methacrylate pairs is readily achieved using secondary ions derived from both the polymer backbone and pendant groups. Principal component analysis (PCA) is performed on the SIMS spectra of the 16 polymers, whereby the resulting principal components are able to distinguish phenyl from benzyl groups, mono‐functional from multi‐functional monomers and acrylates from methacrylates. The principal components are applied to copolymer series to assess the predictive capabilities of the PCA. Beyond being able to predict the copolymer ratio, in some cases, the SIMS analysis is able to provide insight into the molecular sequence of a copolymer. The insight gained in this study will be beneficial for developing structure–function relationships based upon ToF‐SIMS data of polymer libraries. © 2016 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.
Highlights
IntroductionSurface analysis plays a key role in the development of materials as it is the surface of a material that will interact with its surrounding environment, thereby determining its function.[1,2,3,4,5] As a material’s surface can differ from the bulk,[6] it is the surface properties rather than bulk composition that should be utilised to elucidate structure–function relationships used for further material optimisation for applications involving interfacial contact of the material with its surroundings.[7,8,9,10] This is relevant when large libraries of materials or material gradients are being assessed as these systems allow the response of a certain environment to large groups or populations of materials to be assessed, and provide a robust insight into underlying interactions.[11,12,13] The polymer microarray format has become a key enabling tool for materials discovery and development,[14,15,16,17,18,19,20] whereby hundreds to thousands of unique polymers are printed onto a single glass slide allowing for parallel screening
Epoxy-functionalized glass slides (Molecular Devices, Sunnyvale, CA, USA) were dip coated in 4% (w/v) poly(hydroxy ethylmethacrylate)
To assess the print quality of the array,[6] phase contrast images (Fig. 2(A)) along with ToF-SIMS ion images of the C6H5+ ion associated with the printed polymers and the C2H5O+ ion associated with the poly(hydroxy ethylmethacrylate) (pHEMA) background were produced (Fig. 2(B and C))
Summary
Surface analysis plays a key role in the development of materials as it is the surface of a material that will interact with its surrounding environment, thereby determining its function.[1,2,3,4,5] As a material’s surface can differ from the bulk,[6] it is the surface properties rather than bulk composition that should be utilised to elucidate structure–function relationships used for further material optimisation for applications involving interfacial contact of the material with its surroundings.[7,8,9,10] This is relevant when large libraries of materials or material gradients are being assessed as these systems allow the response of a certain environment to large groups or populations of materials to be assessed, and provide a robust insight into underlying interactions.[11,12,13] The polymer microarray format has become a key enabling tool for materials discovery and development,[14,15,16,17,18,19,20] whereby hundreds to thousands of unique polymers are printed onto a single glass slide allowing for parallel screening. In a recent study, a correlation was observed between bacterial attachment to polyacrylates with a composite parameter derived from molecular descriptors associated with molecular rigidity and hydrophobicity. This was made possible by the large number of bacterial–material interactions that were assessed using the polymer microarray.[13]
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