Physical interpretations of multimodal AFM contrast on soft materials

G. Haugstad
University of Minnesota,
United States

Keywords: AFM, soft materials


In this work we quantitatively analyze up to eight AFM measurables that can generate materials contrast on soft matter, including (i) sliding friction force in contact mode; (ii, iii) adhesion and contact stiffness in force-distance curve mapping (both slow and fast variants, e.g. "force volume" and "peakforce" modes), (iv, v) phase imaging in net attractive- and net repulsive-regime dynamic/AC mode (aka traditional amplitude-modulation "tapping mode"); (vi, vii) contact resonance amplitude and frequency under pulsed-IR excitation (aka resonance-enhanced mode on a Bruker NanoIR3 AFM-IR system); (viii) Fourier-reconstructed conservative and dissipative force versus distance relationships analyzed and mapped using machine learning in intermodulation mode (i.e., IntermodulationProducts AB Multi Lockin Analyzer / software system). We apply select combinations of these methods to polymer blends, nanostructured single-layer and multi-layer coatings, two-surfactant and surfactant/nanoparticle ultrathin films, and polymer/small-molecule (e.g., drug) mixtures, all being systems of interest to our industrial as well as academic collaborators. We seek improved understandings of (i) complementary information obtained (mechanical, tribological, surface energy, chemical) as well as (ii) methodological limitations and optimizations.