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This paper addresses the effect of polyelectrolyte stiffness on the surface structure of polyelectrolyte (P)/surfactant (S) mixtures. Therefore, two different anionic Ps with different intrinsic persistence length l P are studied while varying the salt concentration (0–10–2 M). Either monosulfonated polyphenylene sulfone (sPSO2-220, l P ∼20 nm) or sodium poly­(styrenesulfonate) (PSS, l P ∼1 nm) is mixed with the cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) well below its critical micelle concentration and studied with tensiometry and neutron reflectivity experiments. We kept the S concentration (10–4 M) constant, while we varied the P concentration (10–5–10–3 M of the monomer, denoted as monoM). P and S adsorb at the air/water interface for all studied mixtures. Around the bulk stoichiometric mixing point (BSMP), PSS/C14TAB mixtures lose their surface activity, whereas sPSO2-220/C14TAB mixtures form extended structures perpendicular to the surface (meaning a layer of S with attached P and additional layers of P and S underneath instead of only a monolayer of S with P). Considering the different P monomer structures as well as the impact of salt, we identified the driving force for the formation of these extended structures: compensation of all interfacial charges (P/S ratio ∼1) to maximize the gain of entropy. By increasing the flexibility of P, we can tune the interfacial structures from extended structures to monolayers. These findings may help improve applications based on the adsorption of P/S mixtures in the fields of cosmetic or oil recovery.

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A nematic liquid crystal (LC) was doped with a reactive mixture of a mesogenic diacrylate monomer, a monofunctional acrylate monomer, and photoinitiator. This mixture was filled in transparent test cells with planar electrodes and uniform director alignment. Photopolymerization of the monomers was excited by exposure with ultraviolet light. After photoexposure, the test cells were electrically addressed and their electro-optic response properties were studied by polarized optical microscopy. The voltage dependence of the optical retardation was investigated with a Berek tilting compensator. By applying voltages in the range 4−20 V, the optical retardation was continuously tuned. Importantly, the induced optical phase shift had a smooth onset, which is desirable in electro-optic modulators. Low driving voltages of <15 V were sufficient to induce a half-wavelength retardation throughout the visible spectral range. The time dependence of the transmittance was investigated with monochromatized light and converted to optical phase shift data. Square wave signals (2 kHz) of various amplitudes were switched on and subsequently switched off, respectively. The response times were extracted from the measured data, and sums (t on + t off ) < 3 ms were found at driving voltages of 12−20 V. The copolymer network LC was suitable for 500 Hz modulations. The electro-optic properties of samples with and without added acrylate monomer were compared.

The modelling of scattering data from foams is very challenging due to the complex structure of foams and is therefore often reduced to the fitting of single peak positions or feature mimicking. This article presents a more elaborate model to describe the small-angle neutron scattering (SANS) data from foams. The model takes into account the geometry of the foam bubbles and is based on an incoherent superposition of the reflectivity curves arising from the foam films and the small-angle scattering (SAS) contribution from the plateau borders. The model is capable of describing the complete scattering curve of a foam stabilized by the standard cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) with different water contents, i.e. different drainage states, and provides information on the thickness distribution of liquid films inside the foam. The mean film thickness decreases with decreasing water content because of drainage, from 28 to 22 nm, while the polydispersity increases. These results are in good agreement with the film thicknesses of individual horizontal foam films studied with a thin-film pressure balance.