Interactions between Sulfobetaine-Based Polyzwitterions and Polyelectrolytes
We investigate the interactions between sulfobetaine-based polyzwitterions and polyelectrolytes, either positive or negative ones, i.e., poly(DADMAC)s and poly(AA)s. Three different sulfobetaine motifs denoted SPE, SPP, and SHPP have been considered, presenting slight chemical changes either in the...
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Published in | The journal of physical chemistry. B Vol. 112; no. 8; pp. 2299 - 2310 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
28.02.2008
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Online Access | Get full text |
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Summary: | We investigate the interactions between sulfobetaine-based polyzwitterions and polyelectrolytes, either positive or negative ones, i.e., poly(DADMAC)s and poly(AA)s. Three different sulfobetaine motifs denoted SPE, SPP, and SHPP have been considered, presenting slight chemical changes either in the function carrying the zwitterionic group or in the zwitterionic motif itself. All three poly(sulfobetaine)s normally present critical temperatures (T c) above which they become fully soluble. The association with polyelectrolytes directly affects the critical temperature in a highly nonmonotonic fashion as the mixture composition is varied. Thanks to layer-by-layer deposition in a reflectometric cell, we demonstrate that a selective attraction exists between polyzwitterions and polyelectrolytes, from which an association follows at a nanoscopic scale as demonstrated by small-angle X-ray scattering and atomic force microscopy. The association of polyzwitterions with polyelectrolytes, however, is site-specific since it exists only between positive polyelectrolytes (i.e., polycations) and polyzwitterions based on SPE or SPP motifs. The range in which the association affects the critical temperature, T c, is found to largely depend on the molecular weights of both zwitterionic and cationic species. As a result, the complexation and the creation of a hybrid object, referred to as a complex, also depend on the same parameters. By varying the latter from a few thousands to several millions, we define rules for the existence of this complex. In particular, a minimum polyzwitterion molecular weight is needed to observe alterations of the critical temperatures and closure of the complexation cone. Finally, within a Flory-like approach, we consider the polyzwitterion/polyelectrolyte complex as an effective statistical copolymer, whose composition comprises a fraction φA of excess zwitterionic motifs as the majority species and a fraction 1 − φA of complex motifs. We thereby reduce a polymer/polymer/solvent ternary system to a copolymer/solvent binary one, an assumption valid within the limit of small additions of cationic species. The approach predicts the reciprocal critical temperature 1/T c to be quadratic in φA, which agrees very well with all experimental results, even for a large mismatch between the molecular weights of both species, and regardless of the zwitterionic motif, SPE or SPP. |
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Bibliography: | ark:/67375/TPS-NCFPC8Z6-2 istex:E6164BB5C2C51F356E1D77560259DC9F8A1F0740 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1520-6106 1520-5207 |
DOI: | 10.1021/jp0769274 |