Regensburg 2013 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 36: Poster: (Hydro)gels and Elastomers
CPP 36.7: Poster
Wednesday, March 13, 2013, 16:30–18:30, Poster C
About the elastic nature of the demixing transition of aqueous PNIPAM solutions — •Martine Philipp1, Ulrich Müller2, Ralitsa Aleksandrova2, Roland Sanctuary2, Peter Müller-Buschbaum1, and Jan K. Krüger2 — 1TU München, Physik-Department, LS Funktionelle Materialien, Garching, Germany — 2Université du Luxembourg, LPM, Luxembourg, Luxembourg
The demixing transition of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAM) has been widely investigated in basic and applied research. It is of the lower critical solution temperature type. Due to the large volume change accompanying this phase separation, it is denoted as a volume transition. Only few experiments were dedicated to the elastic properties at this transition. However, one hint exists that the longitudinal elastic modulus may be its inverse order parameter susceptibility [1]. Here we discuss the competitive behaviour of mass density and the longitudinal elastic modulus across the demixing transition in dependence of temperature and PNIPAM concentration [2]. Brillouin spectroscopy indeed proves the governing role of the longitudinal elastic modulus for this phase separation mechanism. Moreover, Brillouin spectra recorded across the phase transition allow following the growth of PNIPAM-rich agglomerates with gel-like mechanical consistency embedded in the liquid PNIPAM-poor phase. This result clearly disproves the widespread opinion that the demixed PNIPAM-rich agglomerates are glassy.
[1] S. Hirotsu, Phase Transitions 47, 183 (1994) [2] M. Philipp, U. Müller, R. Aleksandrova et al., Soft Matter 8, 11387 (2012)