Self-Aggregation of Mixtures of Oppositely Charged Polyelectrolytes and Surfactants Studied by Rheology, Dynamic Light Scattering and Small-Angle Neutron Scattering

Abstract

In this study, the phase behavior, structure and properties of systems composed of the cationic, cellulose-based polycation JR 400 and the anionic surfactants sodium dodecylbenzenesulfonate (SDBS) or sodium dodecylethoxysulfate (SDES), mainly in the semidilute regime, were examined. This system shows the interesting feature of a very large viscosity increase by nearly 4 orders of magnitude as compared to the pure polymer solution already at very low concentrations of 1 wt%. By using rheology, dynamic light scattering (DLS), and small-angle neutron scattering (SANS), we are able to deduce systematic correlations between the molecular composition of the systems (characterized by the charge ratio Z=[+(polymer)]/[−(surfactant)]), their structural organization and the resulting macroscopic flow behavior. Mixtures in the semidilute regime with an excess of polycation charge form highly viscous network structures containing rodlike aggregates composed of surfactant and polyelectrolyte that are interconnected by the long JR 400 chains. Viscosity and storage modulus follow scaling laws as a function of surfactant concentration (η~c(s)(4); G(0)~c(s)(1.5)) and the very pronounced viscosity increase mainly arises from the strongly enhanced structural relaxation time of the systems. In contrast, mixtures with excess surfactant charges form solutions with viscosities even below those of the pure polymer solution. The combination of SANS, DLS, and rheology shows that the structural, dynamical, and rheological properties of these oppositely charged polyelectrolyte/surfactant systems can be controlled in a systematic fashion by appropriately choosing the systems composition.

Testing Classical Approach to Polymer Solutions on SAXS Data of λ-Carrageenan, κ-Carrageenan and Methylcellulose Systems

“…This approach was namely originally developed and then also successfully applied mainly to the SANS data. [7][8][9][10][11][12][13][14][15] Even though there are some similar studies available also on the SAXS data nowadays, we still miss thorough systematic reports on such analysis of experimental SAXS data. The lack of such studies could be reasoned by the necessity of some additional considerations that must be dealt with the SAXS data, i.e.…”

“…As in our experiment the q min was 0.06 nm -1 the resolution was around 52 nm. However, in the case when the static correlation length Ξ is above the resolution of the experiment, one is still able to resolve the value for the dynamic correlation length with satisfactorily precision by simply utilizing the Equation (1) or better Equation (10) and by taking into account only the outer part of the scattering curves obeying the following rule: 9 (13) where q min corresponds to the lowest value of the scattering vector that can still be considered in the fitting procedure. In Figure 2 we depict the results of such an approach on an example of the SAXS curve of 2 wt.…”

“…For the evaluation and interpretation of the SAXS data we followed and adequately modified the so-called "classical approach" developed for the interpretation of similar SANS data on polymer solutions and gels. This approach was already extensively used and tested in the case of SANS on polymer solutions and simple gels [8][9][10][11][12][13][14][15] and recently already also on some SAXS data. [16][17][18][19] In the case of SAXS data one needs to account for the experimental broadening effects and correspondingly slightly modify the fitting scattering function.…”

Complexes of oppositely charged polyelectrolytes and surfactants – recent developments in the field of biologically derived polyelectrolytes

“…A similar behaviour can be observed for the addition of oppositely charged surfactants to polyelectrolytes and several such experiments have been carried out with cellulose based polyelectrolytes. 71,76,77,90 Initially, a somewhat higher viscosity as compared to water is observed due to the polyelectrolyte (see Fig. 6a and 2a for the case of JR 400 as the polyelectrolyte).…”

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

“…Such behaviour is characteristically observed for viscoelastic networks with physical cross-links. 79,80 Interestingly, the slower modes become more prominent when going from the 2-arm to the 4-arm polymer. This indicates that the tendency for aggregation increases with the number of arms.…”