Ion partitioning and ion size effects on streaming field and energy conversion efficiency in a soft nanochannel

• Published in: Colloid and polymer science 2022-09, Vol.300 (9), p.1049-1062
• Main Authors: Kundu, Dipankar, Bhattacharyya, S., Gopmandal, Partha P.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Charge density; Chemistry; Chemistry and Materials Science; Complex Fluids and Microfluidics; Efficiency; Energy conversion efficiency; Food Science; Ion transport; Mathematical models; Nanochannels; Nanotechnology and Microengineering; Original Contribution; Partitioning; Permittivity; Physical Chemistry; Polyelectrolytes; Polymer Sciences; Pore size; Rigid walls; Size effects; Soft and Granular Matter; Transport equations
• ISSN: 0303-402X; 1435-1536
• DOI: 10.1007/s00396-022-05007-8

Numerical modeling on streaming field and electroviscous effect in a soft nanochannel is made by considering the finite ion size and ion partitioning effects. The standard electrokinetic model is modified by incorporating the finite ion size effect and the effect of ion partitioning, which arises due to the difference in dielectric permittivity between the electrolyte and wall grafted polyelectrolyte layer (PEL). Such modification in the ion transport equations enable us to consider higher range of wall charge density as well as higher volumetric charge density of the PEL. The dielectric permittivity of the PEL may become lower due to the large accumulation of counterions drawn by the PEL immobile charges. The ion steric repulsion is taken into account through the BMCSL (Boublik-Mansoori-Carnahan-Starling-Leland) equation based on the hard-sphere model of ions. This enables to consider different ion sizes, which arise when a mixture of different salts is considered. The governing equations are solved numerically and the streaming field is determined iteratively. We find that the ion steric interactions and ion partitioning effects create a counterion saturation. This leads to a reduction in the counterion condensation of the PEL when the PEL and wall are similarly charged, which results in higher streaming field and energy conversion efficiency. The diffuse PEL of pore size in the order of the channel half height creates higher energy efficiency compared to the channel consisting of rigid walls. Graphical abstract