Counterions and Water in Polyelectrolyte Multilayers:  A Tale of Two Polycations

• Published in: Langmuir Vol. 23; no. 2; pp. 896 - 901
• Main Authors: Jaber, Jad A, Schlenoff, Joseph B
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 16.01.2007
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Water; Multilayer; Ionic solution; Doping; Polymer; Perchlorates; Free energy; Sulfonate; Polyelectrolyte; Infrared spectrometry; Association; Polycation; Ionic strength; Chlorides; Water content; Electrochemistry; pH; Counter ion; Protonation; Thermodynamic properties; Interaction energy; Reflectance
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la061839g

Attenuated total internal reflectance Fourier transform infrared, ATR-FTIR, spectroscopy was used to compare the water uptake and doping within polyelectrolyte multilayers made from poly(styrene sulfonate), PSS, and a polycation, either poly(allylamine hydrochloride), PAH, or poly(diallyldimethylammonium chloride), PDADMAC. Unlike PDADMA/PSS multilayers, whose water content depended on the solution ionic strength, PAH/PSS multilayers were resistant to doping by NaCl to a concentration of 1.2 M. Using (infrared active) perchlorate salt, the fraction of residual counterions in PDADMA/PSS and PAH/PSS was determined to be 3% and 6%, respectively. The free energy of association between the polymer segments, in the presence of NaClO4, was about 5 kJ mol-1 and −10 kJ mol-1, respectively, for PDADMA/PSS and PAH/PSS, indicating the relatively strong association between the polymer segments in the latter relative to the former. Varying the pH of the solution in contact with the PAH/PSS multilayer revealed a transition to a highly swollen state, interpreted to signal protonation of PAH under much more basic conditions than the pK a of the solution polymer. The increase in the multilayer pK a suggested an interaction energy for PAH/PSS in NaCl of ca. 16 kJ mol-1.