Anomalous diffusion in an electrolyte saturated paper matrix

Sankha Shuvra Das, Sumeet Kumar, Sambuddha Ghosal, Sandip Ghosal, Suman Chakraborty*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Diffusion of colored dye on water saturated paper substrates has been traditionally exploited with great skill by renowned water color artists. The same physics finds more recent practical applications in paper-based diagnostic devices deploying chemicals that react with a bodily fluid yielding colorimetric signals for disease detection. During spontaneous imbibition through the tortuous pathways of a porous electrolyte saturated paper matrix, a dye molecule undergoes diffusion in a complex network of pores. The advancing front forms a strongly correlated interface that propagates diffusively but with an enhanced effective diffusivity. We measure this effective diffusivity and show that it is several orders of magnitude greater than the free solution diffusivity and has a significant dependence on the solution pH and salt concentration in the background electrolyte. We attribute this to electrically mediated interfacial interactions between the ionic species in the liquid dye and spontaneous surface charges developed at porous interfaces, and introduce a simple theory to explain this phenomenon.

Original languageEnglish (US)
Pages (from-to)678-683
Number of pages6
Issue number9
StatePublished - May 1 2020


  • diffusion
  • diffusiophoresis
  • electrokinetic
  • paper matrix

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry


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