InterPore2026

Diffusion-controlled and irreversible polyelectrolyte adsorption in nanoporous medium

19 May 2026, 15:05

1h 30m

Poster Presentation (MS06) Interfacial phenomena across scales Poster

Speaker

Nicolas Jouault (Laboratoire PHENIX)

Description

The understanding and, in fine, control of the transport properties of charged polymers, i.e. polyelectrolytes (PEs), inside nanoporous media is important to design new devices for nanofluidic or for biological applications such as sequencing of DNA strands or designing pores for biosensors, filtration or chemical separation. In particular, the geometrical constraints imposed by the nanoporous medium and the existence of charges inside may modify interfacial phenomena such as the diffusion and adsorption of PE chains.

Here we propose to address such phenomena through the use of anodic aluminum oxide (AAO) membranes (synthesized in the lab) as model nanoporous medium. First, extensive characterization has shown that AAOs are made of non-connected, parallel cylindrical and monodisperse nanochannels with perfectly tunable diameters, Dp (10-100 nm), interpore distance, Dint (50-150 nm), and length, Lp (10 to 60 μm, see SEM section view in fig. 1) [1,2]. When immersed in solution, the AAO wall charge depends on pH and the isoelectric point of the walls is around pH=9 [3,4]. At low pH (< 6) the AAO walls are then positively charged, while at high pH (> 10) they are negatively charged. Then, multiple transverse streaming potential measurements have been carried out to monitor, through the ζ-potential determination of the wall surface, the penetration of a well-known PE, sodium polystyrene sulfonate (NaPSS) in AAO [3]. A typical ζ-potential evolution with time can be described as follows. At t=0, the AAO is positively charged and, in contact with PE, a charge reversal from positive to negative can be observed until the ζ-potential stabilizes at a constant value, suggesting a gradual adsorption of PE chains at the surface until equilibrium is reached. Our analysis of the ζ-potential curves for different AAO geometries (Dp, Lp) and PE characteristics (concentration or molecular weight) reveals that PE penetration is driven by diffusion and that adsorption is irreversible. Additional X-ray fluorescence imaging experiments, an analytical technique with high spatial resolution, have been performed to map the amount of PE as a function of PE penetration time. It confirms the gradual penetration and adsorption along the nanochannel correlating well with the ζ-potential variation. All combined, it leads us to propose a model to explain all the results: the first PE chains adsorb onto the first accessible sites on the AAO and the following chains must gradually diffuse along the channel to find the next available free sites, and so on until the surface is fully saturated (see Scheme in Fig. 1).

So far, the kinetic of penetration has not been addressed quantitatively because the estimated quantity of PE inside AAO is low (hundreds of ppm), preventing the use of classical analytical techniques. Our results shows that the diffusion and adsorption mechanism of PE inside nanoporous medium can be quantitatively assessed by combining streaming potential experiments and X-ray fluorescence imaging.