Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 11: Responsive and Adaptive Systems

CPP 11.5: Vortrag

Montag, 12. März 2018, 12:15–12:30, C 230

Thermo-Responsive Foams from Aqueous Hydroxylpropyl Cellulose Solutions — •Eric Weißenborn and Björn Braunschweig — Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany

We have studied the ability of hydroxypropyl cellulose (HPC) with a molecular weight of 1 MDa to switch macroscopic foam reversibly from stable to unstable conditions. At 25^∘C room temperature, foams from 0.5 µM HPC are extremely stable with lifetimes of several hours. However, we can dramatically reduce the foam stability by increasing the temperature to 50^∘C which is well above the lower critical solution temperature (LCST) of 45^∘C. In order to clarify the underlying mechanism, we investigated the adsorption of HPC at the air/water interface by recording dynamic surface tensions using the pendant drop method. In addition, UV-VIS spectroscopy and dynamic light scattering indicate the formation of aggregates in the bulk for temperatures above the LCST. Bulk rheology of HPC dilutions shows that at these temperatures, the solutions viscosity is substantially decreased and as a consequence the foam drainage is increased. The latter decreases the foam stability, because foam drainage is one of the major destabilization mechanisms in this system. A fast reduction of temperature from 50^∘C to 25^∘C solubilizes the polymer reversibly and leads to a stabilization of the foam back to its initial stability.