Polyelectrolytes (PEs) are polymers carrying electric charges due to the dissociation in polar solvents of ionic groups present on the chain. Compared to neutral polymers, the existence of theses charges has direct consequences of the PEs behavior in solution or on surfaces [1,2]. In particular, the PE adsorption on concave surfaces has been less studied[3] while it is typically encountered in nanoporous materials and have interesting potential applications such as ionic separation[4], catalysis[5] or ionic rectification for single molecules analysis[6].

During this internship, we propose to study the penetration and adsorption of PE inside a nanoporous membrane whose surface is already covered with a neutral polymer (polyethylene glycol, PEG). If the PE attracts more strongly with the AAO surface, it will displace the neutral polymer to adsorb at the surface. Our aim is to better understand this neutral polymer/PE exchange and to investigate what parameters influence the rate of displacement : electrostatic interaction, polymer charge density, molecular weight Mw...

We will use nanoporous anodic aluminum oxide (AAO) membrane as a model nanoporous system, which is composed of parallel and non-connected nanochannels with variable characteristic sizes (diameter from 10 to 200 nm and length up to 500 μm)[7]. A typical scanning electron microscopy image of the AAO top surface is shown in Fig. 1. We’ll follow the kinetic of exchange between the neutral polymer and the PE by streaming potential measurements[8]. This technique provides information about the surface charge of the AAO, more precisely the ζ-potential. At neutral pH (like in pure water) the bare AAO is positively charged. When covered with neutral polymer the ζ-potential remains slightly positive. Then, if a negative PE is entering and adsorbs at the surface, the surface charge will become negative. Then, the evolution of the ζ-potential with time will allow us to extract a characteristic time of displacement and to monitor the PE exchange kinetics in AAO. A parametric study will be performed to investigate the influence of nanochannel diameter, neutral polymer molecular weight Mw and concentration and nature of PE (weak or strong PE with different Mw)) on the PE exchange in charged nanochannels.

Specific techniques or methods
Synthesis of nanoporous alumina by anodization, scanning electron microscopy, streaming potential measurements, flow measurements.

Refs :
[1] M. Muthukumar, Macromolecules 50, 9528 (2017).
[2] A. V. Dobrynin and M. Rubinstein, Progress in Polymer Science 30, 1049 (2005).
[3] A. Christoulaki, A. Chennevière, E. Dubois, and N. Jouault, Nanoscale 11, 2148 (2019).
[4] J. A. Armstrong, E. E. L. n. Bernal, A. Yaroshchuk, and M. L. Bruening, Langmuir 29, 10287 (2013).
[5] D. M. Dotzauer, J. Dai, L. Sun, and M. L. Bruening, Nano Letters 6, 2268 (2006).
[6] M. Ali, B. Yameen, J. Cervera, P. Ramírez, R. Neumann, W. Ensinger, W. Knoll, and O. Azzaroni, J. Am. Chem. Soc 132, 8338 (2010).
[7] A. Christoulaki, A. Chenneviere, I. Grillo, L. Porcar, E. Dubois, and N. Jouault, Journal of Applied Crystallography 52, 745 (2019).
[8] A. Christoulaki, D. Lairez, E. Dubois, and N. Jouault, ACS Macro Letters 9, 794 (2020).

Candidate’s profile : Master 2 student. She/he should have a background in chemistry, physics or
materials science and an interest for lab experiments.
Internship duration and location : 5-6 months (starting mid-January) in the PHENIX laboratory on
the Pierre and Marie Curie campus (https://www.phenix.cnrs.fr)
Contact : nicolas.jouault@sorbonne-universite.fr (personal webpage :
https://www.phenix.cnrs.fr/spip.php?rubrique238)