Regensburg 2025 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: Responsive and Adaptive Polymers

CPP 31.3: Talk

Wednesday, March 19, 2025, 17:00–17:15, H38

Critical analysis of adhesion work measurements from AFM-based techniques for soft contact — Dmitrii Sychev^{1, 2}, Simon Schubotz^{1, 2}, Quinn A. Besford¹, Andreas Fery^{1, 3}, and •Günter K. Auernhammer¹ — ¹Leibniz-Institut für Polymerforschung Dresden e.V., Dresden, Germany — ²TU Dresden, Germany — ³Chair of Physical Chemistry of Polymeric Materials,TU Dresden, Germany

The work of adhesion is a thermodynamic quantity that is frequently measured by atomic force microscopy (AFM). Its determination requires quasi-equilibrium measurements. Here, we address the question of to what extent atomic force microscopy qualifies for quasi-equilibrium measurements. To measure the work of adhesion, we combined soft colloidal probe AFM (SCP AFM) with reflection interference contrast microscopy (RICM). We extract the work of adhesion either from the pull-off force or from the contact radius to measure the adhesion behavior of poly(N-isopropylacrylamide) (PNIPAM) polymer brushes in the swollen and solvent-induced collapsed state. In the swollen state, the adhesion to the PNIPAM brush was fivefold larger and exhibited significant time dependencies when measured with SCP AFM. A strong rate dependence of the pull-off force method was indicative of a non-equilibrium process. In order to reliably determine the equilibrium work of adhesion, the contact radius method was found to be the better because it is not rate dependent. In summary, using optical measurements to determine the contact radius is beneficial when deriving the works of adhesion between colloidal probes and polymer brush surfaces.

Keywords: AFM; Reflection interference contrast microscopy; Adhesion; Polymer brushes