Temperature-Dependent Transport Properties of Poly [2-(methacryloyloxy)ethyl] Trimethylammonium Chloride Brushes Resulting from Ion Specific Effects

T. ALONSO-GARCÍA; C. GERVASI; M.J. RODRÍGUEZ-PRESA; E. GUIÉRREZ-PINEDA; S.E. MOYA; O. AZZARONI

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 vol. 117 p. 26680 - 26688

1932-7447

Combined use of electrochemical techniques (electrochemical impedance spectroscopy and cyclic voltammetry) and quartz crystal microbalance with dissipation allowed to resolve separately the thermal effects on diffusion and electron-transfer steps of the electrochemical reaction of the [Fe(CN)6]3?/4? redox couple at a Au electrode modified with poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PMETAC) brushes. Arrhenius-type dependences of the kinetic constant and the diffusion coefficient with temperature were observed in different electrolytes. Ion-paired collapsed polyelectrolyte brushes in NaClO4 result in compact stiff structures with less amount of entrapped water and markedly different from the same brushes with a collapse driven by pure Coulombic screening in NaCl. A remarkable difference related to the type of counterion is the occurrence of a thermal transition for the polyelectrolyte brush in the presence of ClO4? ions at near-ambient temperature (17 °C). Activation energies for electron-transfer and diffusion processes become twice as large as those for temperatures above the thermal transition. These electrochemical studies demonstrate not only the critical role of ion-pairing interactions in determining the physicochemical properties of the macromolecular system but also provide experimental evidence of counterion-induced thermocontrolled transport functionality in the polyelectrolyte brush layer.