Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

Abstract

SummarySignificant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip–sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young’s modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip–sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information.

High-stress study of bioinspired multifunctional PEDOT:PSS/nanoclay nanocomposites using AFM, SEM and numerical simulation

“…The contact-resonance frequency and quality factor are often referred to as mechanical parameters. Although, there are methods to approximately calibrate for the Young’s modulus, they require a standard reference sample with similar properties to the unknown sample, and this includes the surface properties [ 51 ]. Additionally, polymer mechanical properties are very sensitive to the frequency of the measurement due to their viscoelasticity (rate-dependent behavior) [ 52 ].…”

Nanorheology of living cells measured by AFM-based force–distance curves

“…Several FDC experiments have revealed that the approach and retraction sections of force-distance curves performed on mammalian cells do not overlap. 3,41,50 The hysteresis observed in a FDC is either a consequence the existence of energy-dissipation processes inside a material 59,60 or produced by the breaking of the plasma membrane. Force-distance curves acquired sequentially on a single cell are very reproducible, 3,41 therefore, we conclude that the hysteresis is dominated by dissipative processes occurring inside the cell.…”

Fast, quantitative and high resolution mapping of viscoelastic properties with bimodal AFM

“…Among other issues, there is no established and generally accepted framework to measure the viscoelastic properties from AFM experiments. 1,6,8,[16][17][18][19][20][21] Bimodal AFM provides a very fast, high resolution and accurate method to map the elastic properties of polymers and biomolecules. 22,23 It has been applied to determine with very high spatial resolution the elastic modulus of a large variety of materials and macromolecules such as antibodies 24 and other proteins, [25][26][27] DNA, 28,29 cells, 30,31 bone microconstituents, 32 lipid bilayers, 33,34 self-assembled monolayers, 35,36 2D materials 37 or organic semiconductor devices.…”