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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 8: Wetting, Fluidics and Liquids at Interfaces and Surfaces II (joint session CPP/DY)
CPP 8.5: Talk
Monday, March 9, 2026, 12:30–12:45, ZEU/0260
Tuning Sliding Drop Shape — •Fiona Berner, Chaurasia Rishi, Sajjad Shumaly, Chirag Hinduja, Hans-Jürgen Butt, and Rüdiger Berger — Max-Planck-Institut für Polymerforschung
The understanding of wetting phenomena plays a crucial role in many daily processes. For example, dirt repelling glasses can be achieved by a hydrophobic coating. Recently, Hinduja et al, reported on a scanning drop friction force instrument (sDoFFI) to analyse friction forces of drops on surfaces. A drop is fixated to an elastic force sensor with spring constant κ. The sample underneath the drop is moved with a constant speed u leading to sliding of the drop at a defined trajectory along surfaces. The deflection of the capillary,d, provides information about the friction force between the drop and the surface, Fmeas=κ · d Forces arising from CAH are given by the Furmidge equation, where the drop*s sliding force FCAH corresponds to F_CAH=k ·γ·w·(cos(θ_rec) -cos(θ_adv)) where k is a geometrical factor, γ is the liquid surface tension, w the width of the drop and θ rec and θ adv are the receding and advancing contact angles, respectively. For small u we assume Fmeas=FCAH. The parameters γ, w, θ rec and θ adv are known or can be measured optically. Thus, the geometrical factor k can be calculated. We realize different geometries of the drop by glueing metal rings to the elastic glass capillary. Shaping the metal rings forces the drop to shape. We discuss experiments where we shape the drop into different width and length and discuss dependence of the geometrical factor k.
Keywords: Drop Friction Force; Shape Factor; Furmidge equation; sDoFFI; Drop Shape