Researchers from the Department of Chemistry Jasmina Jukić, Davor Kovačević, Nikola Cindro and Josip Požar, in collaboration with Rok Fink, Martina Oder and Ana-Marija Milisav from the Faculty of Health Sciences, University of Ljubljana, have published the study “Predicting the outcomes of interpolyelectrolyte neutralization at surfaces on the basis of complexation experiments and vice versa” in the Royal Society of Chemistry journal Soft Matter (IF = 3.679).
The paper was featured on the Back Cover of the issue.
The study was carried out with the aim of establishing how the outcomes of polyelectrolyte multilayer formation on a SiO2 surface can be predicted on the basis of the results of complexation studies in solution and vice versa. For this purpose, the correlation between the processes of complex and multilayer formation involving three pairs of vinylic polyions in solutions of binary 1 : 1 sodium salts was explored by means of dynamic and electrophoretic light scattering, potentiometry, microcalorimetry, spectrophotometry and quartz crystal microbalance. The gradual reactant mixing in solution at lower salt concentrations resulted first in formation of primary complexes (with excess titrand on the surface), which have further titration formed secondary complexes (with excess titrant on the surface). Coalescence of the primary and secondary complexes yielded a metastable flocculate which contained approximately equivalent amounts of monomers. Addition of an excess of the titrant to a suspension of the primary complex lead exclusively to the formation of secondary complexes, i.e. a successive charge inversion was achieved, as in the case of the corresponding multilayers. At high salt concentration and with excess polycation present, metastable nano-complexes and precipitates containing surplus of positively charged monomers were formed. The amount of extrinsically compensated charge was in accord with the polycation affinities toward counteranions, established by monitoring the electrolyte-induced aggregation of positively charged nano-complexes. The effect of the electrolyte on the composition of the corresponding multilayers was perfectly analogous, indicating that the processes of interpolyelectrolitic neutralisation in solution and on SiO2 surface are essentially identical.
Aside from providing a deeper understanding of interpolyelectrolyte neutralization, the gained insights can also be used to steer further composition modifications, as well as physical and chemical properties of multilayers through knowledge of the complexation outcomes under different conditions (concentration and types of counterions in the solution). This fact has been used for inchansing antimicrobial properties of multilayers build from poly(allylammonium) cations and poly(styrenesulfonate) anions.
The research was performed as a part of the research project Physical chemistry of processes at mineral/(poly)electrolyte solution interface (IP-2020-02-9571) funded by the Croatian Science Foundation.
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