G. Haugstad, B. Luo, B. Curtin, K. Wormuth
University of Minnesota,
United States
Keywords: AFM-IR, polymer, fibers, Raman
Summary:
In this work we describe industry-collaborative research applying AFM-IR to soft matter technologies such a polymer-drug coatings and fibrous polymeric fabric (pertinent to biomedical devices). In the process we investigate fundamental questions in measurement science, such as the extent of depth-integration of signal, while exploring different modalities ranging from contact resonance to “reverse heterodyne” AC methods (i.e., shaking the cantilever at a higher eigenfrequency while detecting IR absorption at the fundamental or “0th” eigenfrequency). We divulge depth sensitivities ranging from micron-regime at the high end down to tens of nanometers depending on modality, and how this broad range can strongly impact the character of images collected – even qualitatively. This implicitly strong “parameter dependence” is found to be both bane and opportunity to the measurement scientist. A further “sanity check”, as well as complementarity, is provided by hyperspectral confocal Raman microscopy (at hundreds-of-nanometer lateral resolution). Such microscopy comparisons have not been conducted in the large majority of AFM-IR studies reported to date.