Expanding Functionality of Atomic Force Microscopy with High-Speed Environmental Studies
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.77
Expanding Functionality of Atomic Force Microscopy with High-Speed Environmental Studies Sergei Magonov1 and Shijie Wu2 1
SPM Labs LLC, 148 W. Orion Street, Tempe, AZ 85283, U.S.A.
2
Keysight Technologies, 5301 Steven Creek Bld., Santa Clara, CA 95051, U.S.A.
ABSTRACT
Environmental atomic force microscopy (AFM) study of brush macromolecules, polymer blends and bitumen was performed with regular and Quick Scan imaging. Condensation of different vapors on sample surface has induced swelling of hydrophilic domains that helps recognizing the components of heterogeneous compounds. High-resolution imaging of brush macromolecules was achieved in ethyl acetate vapor. Fast monitoring of aggregation/spreading of brush macromolecules revealed dynamics of conformational changes and molecular motion.
INTRODUCTION Atomic force microscopy (AFM) is a unique technique that can be applied to samples in air, gases, vacuum and liquids. Visualization of surface structures and examination of their properties with AFM in vapors of volatile liquids are important for understanding materials' behavior in many practical applications. Environmental studies, which have been implemented in Keysight scanning probe microscopes for many years [1], are further advanced with Quick Scan [2] imaging of surface areas from 100 nm to 100 µm with rates up to 100 Hz. Surface phenomena (swelling, hydration, wetting, etc) of samples in vapors can be monitored on short time scales not available in regular AFM. Environmental imaging is illustrated by studies of swelling of polymer blends, bitumen and monitoring of aggregation/spreading of brush macromolecules on mica. EXPERIMENTAL DETAILS Thin films of polymer blends of atactic polystyrene - PS with poly(methyl methacrylate) – PMMA, PS with poly(vinyl acetate) - PVAC, and a blend of poly(ethylene oxide) - PEO with poly(vinyl pyrrolidone) - PVP were prepared by spin casting of their dilute solutions in toluene on Si and ITO glass. Polymers were purchased from SigmaAldrich. A bitumen (PG64-22) sample was made by annealing a piece of the material on Si at 155˚C for 50 min. Samples of brush polymers on mica were provided by Prof. S. Sheiko (UNC, Chapel Hill). The studies were made with Keysight 9500
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scanning probe microscope in regular and Quick Scan imaging. For study in water, methanol and ethyl acetate vapors a sample was put into a microscope chamber and 0.1 2 ml of the liquids were injected in it. Opening the chamber brings the sample to air. Quick Scan is a concert operation of a small-scanner fast-responding Z-piezo stack and a regular scanner addressing large vertical and lateral displacements. This action is regulated by crossover frequency (25 kHz) with the small actuator operating at higher frequenci
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