2015-06-24
10:15 at HCI J 574

A 2 scale approach to combine continuum simulations of dynamic AFM with soft materials dynamics

Horacio Andres Vargas Guzman

Max Planck Institut für Polymerforschung (MPIP), Mainz

Dynamic atomic force microscopy techniques have been developed in the field of nanoscience. Their most significant milestones go from achieving true atomic resolution in inorganic surfaces to imaging biological system with unprecedented molecular resolutions. A relevant research avenue within those experimental techniques is devoted to the generation of molecular resolution images of soft materials in liquid environments and its mechanical characterization. Despite its impressive experimental development, the technique has some key limitations from the modeling point of view. The modeling framework of AFM dynamic techniques fail to reproduce soft materials phenomena existing in polymeric and biological systems, such as viscoelasticity and/or high deformation regimes. Analytical expressions to estimate the exerted force by an AFM cantilever tip will facilitate the interpretation and allow further development of dynamic AFM techniques, such as the envisioned applications in the medical and advanced materials fields. However there are several constraints while deducing analytical expressions for the exerted force, such as the nonlinear character of the cantilever-tip system. We have deduced a closed-form analytical expression to estimate the tip-sample peak forces while imaging soft materials in liquid environment. Whereby we have combined a multivariate regression analysis with the use of the virial-dissipation method and continuum contact mechanics models. The delivered expression enables to estimate the peak force based on dynamic AFM observables, probe characteristics and the material properties of the sample. Moreover, the accuracy of this expression has been verified but comparing it to numerical simulations of dynamics AFM. Another on-going work is to couple the presented analytical expression for the forces to Coarse Grained (CG) simulations on the target soft material. This will allow us to understand the connection between the measured effective mechanical properties and the simulated dynamics of the targeted materials (e.g. IgM antibody in water), and thus complete the theoretical description of the sample's non- invasive imaging regime with dynamic AFM.