Abstract
Aqueous solutions of polyelectrolytes are studied here by means of neutron scattering, with emphasis on backbone hydrophobicity and counter ion specific effects. Ionene polyelectrolytes with varying chain charge density and different counter ions are considered. Their neutron scattering data feature a number of aspects and trends that clearly deviate from the predictions of the existing theory. Ionenes challenge the current hydrophilic-hydrophobic classification of water-soluble polyelectrolytes. The hydrophobic character of their hydrocarbon backbone emerges only for very low chain charge densities (at 15% of charged monomers), which is significantly lower than for other polyelectrolytes with a more complex structure. Universality in the counter ion specific effect seen in ionene solutions with Br(-) or F(-) counterions is established. The polyelectrolyte peak in the scattering spectra of Br-ionenes disappears beyond a specific charge concentration, which is identical across all ionene chain charge densities. In addition, scattering spectra of Br-ionenes and F-ionenes feature contrasting temperature trends, which are accentuated with decreasing chain charge density. Our interpretation of the F-Br effect, based on the different hydration properties of the counter ions, is supported by additional NMR measurements on ionenes with mixed counter ion clouds. Overall, the study of ionene polyelectrolytes points clearly to the need for combining the scaling concepts with those of ion specificity, to obtain a theoretical framework encompassing the wealth of phenomena occurring in polyelectrolyte solutions.
Highlights
Recent advances have extended the already rich field of polyelectrolyte applications to the very edge of our current technology
We see a gradual disappearance of the polyelectrolyte peak beyond a certain ionene monomer concentration in the case of 12,12-Br ionenes, while the peak remains for 12,12-F ionenes across the entire concentration range studied
Experimental scattering data for ionene polyelectrolytes, systems with a well defined set of structural features, present a number of aspects and trends that deviate both from previous observations on other polyelectrolyte solutions as well as from the predictions of the existing theory based on scaling concepts
Summary
Recent advances have extended the already rich field of polyelectrolyte applications to the very edge of our current technology. Water soluble cationic polyelectrolytes with pH independent charge, based on quaternary ammonium charged centres linked by simple hydrocarbon chains They have already been studied in connection to several applications, including ion exchange resins,[28] water treatment in oil industry,[29] organic templates in the synthesis of mesoporous silica,[30] or anti-microbial agents.[31]. Recent neutron scattering data as well as osmotic coefficients show that across a wide chain charge density, ionenes show surprisingly a hydrophilic character.[35] In addition, a striking counter ion specific effect was reported for 6,9-F and 6,9-Br ionenes.[35] While the former has the signature of a typical hydrophilic PE in the semidilute regime (a clear PE peak over almost three decades in PE monomer concentration, cp, the peak position scaling as cp1/2), the latter features the disappearance of the PE peak beyond a given PE monomer concentration (1 mol dmÀ3).‡.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
