Characterization techniques for polymers and polymeric materials are crucial to innovation and development of the advanced materials field. Atomic force microscopy (AFM) is a powerful characterization technique as it is a nondestructive, high spatial resolution technique that can be used in ambient conditions with minimal sample preparation. Tapping mode AFM imaging, also known as amplitude-modulated (AM) AFM is fast, gentle and can provide images of features ranging from fractions of a nanometer to tens of microns in size. Although tapping mode imaging provides quantitative topography information, until recently, only qualitative mechanical properties of the surfaces could be obtained. AM-FM imaging mode is a bimodal (dual-frequency) technique that provides quantitative contact stiffness data, from which elastic modulus can be calculated with appropriate models for the tip sample contact mechanics. During AM-FM imaging the first resonant mode is operated in AM, whereas a higher resonant mode is frequency modulated (FM). One of the remaining challenges is the calibration of the cantilever’s higher mode spring constant and sensitivity. Here, we will discuss calibration procedure that delivers higher mode cantilever oscillation amplitude in nanometers, which allows for the exact same experimental settings from one experiment to another and we will present results on small-scale and low-dimensional materials. Results on various samples such as metals, alloys and polymers will be presented to demonstrate the applicability of AM-FM mode for materials with a wide range of modulus (MPa-GPa). Furthermore, recent advances in AM-FM imaging will be discussed, such as the use of photothermal excitation to achieve molecular-level resolution on semi-crystalline polymers. With the growing demand for mechanical characterization of polymeric materials at the micro and nanoscale, AM-FM technique provides quantitative nanomechanical information while simultaneously offering all the familiar advantages of tapping mode.

Tapping mode based AFM technique for quantitative characterization of mechanical properties of polymers

253rd National Meeting (2017)

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