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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 4: Interfaces and Thin Films
CPP 4.3: Talk
Monday, March 18, 2024, 10:00–10:15, H 0111
Are refractive index and relative permittivity of an interphase connected to the interfacial adhesion? — •Dorothee Silbernagl1 and Heinz Sturm1,2 — 1BAM, Berlin, Germany — 2TU Berlin, IWF, Germany
Polymer interphases usually form between bulk polymer and more rigid materials. These interphases have distinct physical properties, which can differ significantly from the polymer's bulk properties. Since the dimension of those interphases are usually in the nanometer-scale we chose atomic force microscopy (AFM) force distance curves (FDC) as technique. As sample geometry we chose thin films of poly-n-butylmethacrylate (PnBMA) with different film thicknesses between 30 and 120 nm. This allows for measuring perpendicular to the film-substrate surface with a defined distance to the interface. Additionally, substrates (Si wafers) were etched locally to change the surface' polarity (Si-O versus Si-H-temination), thus tuning the interfacial adhesion of film and substrate from weak to strong. Measuring Young's moduli of such samples we were able to show the influence of interfacial adhesion. The stronger the interfacial adhesion, the higher the substrate's contribution to the overall mechanical properties. Analysis of FDCs' attractive regime revealed that also the measured Hamaker constant correlates with interfacial adhesion, showing higher contribution from the substrate with stronger adhesion. Since the Hamaker constant is derived from refractive index n and relative permittivity ε we hypothesis that - depending on the polymer-substrate adhesion - the polymer interphase inherits the electrodynamic properties of the substrate.
Keywords: polymer; adhesion; interphase; atomic force microscopy; hamaker