Aqueous mixtures of polyelectrolytes and oppositely charged surfactants form clear and homogeneous solutions if either the polyelectrolyte or the surfactant is present in excess. Around charge equilibrium, macroscopic precipitates are formed. Near the phase boundary on the polyelectrolyte-rich side, nanometric polyelectrolyte/surfactant complexes can greatly increase the viscosity of aqueous solutions. This behavior is governed by the composition and chemical nature of the polyelectrolyte and surfactant. Here, we investigate complexes consisting of the polycation JR 400 and two different surfactants, namely, sodium octyl sulfate (SOS) and sodium tetradecyl sulfate (STS), which only differ in the length of their alkyl tail. Using small-angle neutron scattering and neutron spin-echo spectroscopy, we find that STS forms mixed aggregates with JR 400 which results in a pronounced increase in viscosity. Such an increase is not observed for SOS where no mixed aggregates are formed. Comparison with atomistic molecular dynamics simulations shows good qualitative agreement.

Semidilute mixtures of the cationically modified cellulose-based polyelectrolyte JR 400 and the anionic surfactant sodium dodecyl sulfate (SDS) form highly viscous solutions if a slight excess of charges from the polyelectrolyte is present. The reason for this is the formation of mixed rodlike aggregates in which the surfactant cross-links several polyelectrolyte chains. The same solutions also show shear-thinning behavior. In this paper, we use rheoSANS to investigate the structural evolution of the rodlike aggregates under steady shear and thereby elucidate the mechanism of shear-thinning in these viscous oppositely charged polyelectrolyte surfactant complexes.

Graphene is an attractive component for high-performance stimuli-responsive or ‘smart’ materials, shape memory materials, photomechanical actuators, piezoelectric materials and flexible strain sensors. Nanocomposite fibres were produced by electrospinning high molecular weight Polyvinylpyrrolidone (PVP-1300 kDa) in the presence of noncovalently functionalised graphene obtained through tip sonication of graphite alcoholic suspensions in the presence of PVP (10 kDa). Bending instability of electrospun jet appears to progressively increase at low graphene concentrations with the result of greater fibre stretching that leads to lower fibre diameter and possibly conformational changes of PVP. Further increase of graphene content seams having the opposite effect leading to greater fibre diameter and Raman spectra similar to the pure PVP electrospun mats. All this has been interpreted on the basis of currently accepted model for bending instability of electrospun jets. The graphene addition does not lower the very high sound absorption coefficient, α, close to unity, of the electrospun PVP mats in the frequency range 200–800 Hz. The graphene addition affects, in a non-monotonous manner, the bell shaped curves of α versus frequency curves becoming sharper and moving to higher frequency at the lower graphene addition. The opposite is observed when the graphene content is further increased.

Interactions of polyelectrolytes with oppositely charged surfactants can give rise to a large variety of self-assembled structures. Some of these systems cause a drastic increase in solution viscosity, which is...