ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Obstruction scaling model for the diffusion of the outer electrolyte leading to Liesegang patterns of (AgNO₃ + KCl) system in agarose hydrogel

Prasad C. Walimbe, Preeti S. Kulkarni, and Sunil D. Kulkarni

Post Graduate and Research Center, Department of Chemistry, S. P. Mandali’s Sir Parashurambhau College, Savitribai Phule Pune University, Pune, India

E-mail: sunil.kulkarni@spcollegepune.ac.in

Received: 13 June 2021  Accepted: 2 September 2021

Abstract:

Diffusion in hydrogels has gained much attention owing to diverse applications in many areas. The physical diffusion models have been applied to passive diffusion of ions, drug molecules, and macromolecules in polymers solutions and hydrogels and rarely to periodic precipitations (Liesegang patterns) obtained via reaction–diffusion (RD). Classically, the role of gels in RD systems was assumed to be limited to provide mechanical support to the reaction products and to avoid sedimentation. In the present paper, we have employed the AgNO₃ (outer electrolyte)–KCl (inner electrolyte)–agarose (gel matrix) system to identify the role of a hydrogel in the RD system in view of diffusion of outer electrolyte through it. The experiments were performed by varying the agarose volume fractions, keeping the outer and inner electrolyte concentrations constant, and using a 2D classical Liesegang setup. The physical obstruction scaling model (OSM) was applied to arrive at the theoretical diffusion coefficients. The model was validated experimentally by evaluating diffusion coefficients using the time law of the Liesegang patterns. It was observed that, at low volume fractions of gel, the theoretical and the experimental values match within ( ±) 5–20%; however, at high volume fractions, the deviation is > 50%.

Graphical abstract

Keywords: Diffusivities; Reaction–diffusion; Periodic precipitation; Agar hydrogel; Obstruction scaling model

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-021-01858-7

Chemical Papers 76 (1) 329–340 (2022)