Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: Charged Soft Matter I

CPP 22.8: Talk

Tuesday, March 17, 2015, 11:15–11:30, PC 203

New fitting model for refractive index of PSS/PDADMAC polyelectrolyte multilayers swelling in humid conditions — •Oliver Löhmann and Regine von Klitzing — Technische Universität Berlin

Polyelectrolyte multilayers (PEMs) are a versatile approach to functionalize charged surfaces. PEMs can be built up by the Layer-by-layer technique which is an easy and well controllable technique to achieve polymer coatings in nanometer range. Polymer coatings are able to respond to external stimuli, e.g. relative humidity (r.h.), depending on their chemical nature. By increasing the r.h., the water uptake can be split into two types of water: the void water which contributes only to changes in the refractive index and the swelling water which changes both, thickness and refractive index. It is still unclear how the voids are filled with water and so far no model for the water adsorption for PEMs exists.

Here, we will present two different fitting models for the refractive index of PEMs in different humidity: The Garnett model and an extended version of the void model. The swelling behavior of PEMs depending on r.h. was measured by Ellipsometry. The PEMs swell in a non-linear behavior and the volume fraction of adsorbed water is independent of the layer number. We will show that the Garnett model only partly describes the refractive index. Taking the filling of voids at low r.h. into account the refractive index in dependence on the r.h. is fully described. Now, it is possible to calculate the volume fraction of air inside the dry PEMs (voids) and the ability of water uptake.