8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P4.58Fri 911:10-14:00Dielectric relaxations in aqueous polyelectrolytesolutions: the effect of temperatureDomenico Truzzolillo, 1 Stefano Sarti, 2 and Federico Bordi 21 F. O. R. T. H. , Institute of Electronic Structure and Laser, N Plastira 100, 71110,Heraklion, Greece2 Dipartimento di Fisica - Sapienza, Università di Roma, Rome, ItalyDielectric spectroscopy data over the range 100 MHz - 40 GHz allow for a reliable analysis oftwo of the major relaxation phenomena for polyelectrolytes (PE) in water [1]. Within this range,the dielectric relaxation of pure water is dominated by a Debye process at ν = 18.5 GHz correspondingto a relaxation time of τ w = 8.4 ps at 25 ◦ C [2]. This mode is commonly attributed tothe cooperative relaxation specific to liquids forming hydrogen-bond network (HBN) and arisingfrom long range H-bond mediated dipole-dipole interactions. The presence of charged polymers inwater partially modifies the dielectric characteristics of the orientational water molecule relaxationdue to a change of the dielectric constant of water surrounding the charges on the polymer chain.We report experimental results on the effect of the presence of a standard flexible polyelectrolyte(sodium-polyacrylate) on the HBN in water for different temperatures, showing that the HBN relaxationtime is not changed by increasing the polyelectrolyte density in water, even if relativelyhigh concentrations are reached (all data presented are in the semidilute regime). We find that theeffect of PE on HBN is not a shift on the characteristic time nor a ”broadening” of its distribution,rather a decrease of the ”spectral weight” that goes beyond the pure volume fraction effect. Thisdecrease is larger at low T and less evident at high T, supporting the idea that the correlation lengthof the water is less affected by the presence of charged flexible chains at high temperatures. [1]F Bordi, C Cametti, and R H Colby, J. Phys: Cond. Mat, 16(49):R1423, 2004. [2] W. J. Ellison.Journal of Physical and Chemical Reference Data, 36(1):1-18, 2007.58