Probing Polyelectrolyte Adsorption in Charged Nanochannels by Streaming Potential Measurements.

It remains a great experimental challenge to obtain quantitative information on the polyelectrolyte (PE) behavior confined in charged nanoporous materials. Here, we propose an original approach using transverse streaming potential measurements (TSPMs), an efficient technique providing information on the electrical surface properties of nanoporous materials through the ζ-potential determination. We conduct TSPMs within the thin double-layer approximation on a model system composed of individual nanochannels, a nanoporous anodic aluminum oxide (AAO) membrane, filled with a well-known PE, sodium polystyrenesulfonate (NaPSS). We demonstrate that TSPMs can provide the AAO ζ-potential under different experimental conditions and monitor the PE penetration in AAO with positive or negative surface charge. On the positive surface, the PE irreversibly adsorbs, while it does not when the surface is negatively charged, indicating the electrostatic nature of the PE adsorption. In the context of experimental limitations to investigate PE behavior on concave surfaces, this study shows that the TSPM is suitable to extract quantitative information and can be exploited to gain an understanding of the PE adsorption and desorption in a confined medium.

A novel methodology to study nanoporous alumina by small-angle neutron scattering.

Nanoporous anodic aluminium oxide (AAO) membranes are promising host systems for confinement of condensed matter. Characterizing their structure and composition is thus of primary importance for studying the behavior of confined objects. Here a novel methodology to extract quantitative information on the structure and composition of well defined AAO membranes by combining small-angle neutron scattering (SANS) measurements and scanning electron microscopy (SEM) imaging is reported. In particular, (i) information about the pore hexagonal arrangement is extracted from SEM analysis, (ii) the best SANS experimental conditions to perform reliable measurements are determined and (iii) a detailed fitting method is proposed, in which the probed length in the fitting model is a critical parameter related to the longitudinal pore ordering. Finally, to validate this strategy, it is applied to characterize AAOs prepared under different conditions and it is shown that the experimental SANS data can be fully reproduced by a core/shell model, indicating the existence of a contaminated shell. This original approach, based on a detailed and complete description of the SANS data, can be applied to a variety of confining media and will allow the further investigation of condensed matter under confinement.

Duplex nanoporous alumina and polyelectrolyte adsorption: more insights from a combined neutron reflectivity and electron microscopy study.

Neutron reflectivity (NR) is a powerful technique to investigate the incorporation of nanomaterials (polymers, nanoparticles, etc) into multilayer porous systems. Here we propose an experimental approach combining NR and scanning electron microscopy (SEM) to successfully characterize duplex nanoporous anodic aluminum oxides (nAAO) and to extract quantitative information about the entering and adsorption of polyelectrolytes (PEs) in nanopores. Duplex nAAO are promising systems to study the influence of geometrical constriction, i.e. the reduction of pore diameters along the pore channel, on the confinement of condensed matters.

Complexation of lysozyme with adsorbed PtBS-b-SCPI block polyelectrolyte micelles on silver surface.

We present a study of the interaction of the positively charged model protein lysozyme with the negatively charged amphiphilic diblock polyelectrolyte micelles of poly(tert-butylstyrene-b-sodium (sulfamate/carboxylate)isoprene) (PtBS-b-SCPI) on the silver/water interface. The adsorption kinetics are monitored by surface plasmon resonance, and the surface morphology is probed by atomic force microscopy. The micellar adsorption is described by stretched-exponential kinetics, and the micellar layer morphology shows that the micelles do not lose their integrity upon adsorption. The complexation of lysozyme with the adsorbed micellar layers depends on the micelles arrangement and density in the underlying layer, and lysozyme follows the local morphology of the underlying roughness. When the micellar adsorbed amount is small, the layers show low capacity in protein complexation and low resistance in loading. When the micellar adsorbed amount is high, the situation is reversed. The adsorbed layers both with or without added protein are found to be irreversibly adsorbed on the Ag surface.