Measuring subdiffusion parameters

We propose a method to extract from experimental data the subdiffusion parameter $α$ and subdiffusion coefficient $D_α$ which are defined by means of the relation $<x^2> =2D_α/Γ(1+α) t^α$ where $<x^2>$ denotes a mean square displacement of a random walker starting from $x=0$ at the initial time $t=0$. The method exploits a membrane system where a substance of interest is transported in a solvent from one vessel to another across a thin membrane which plays here only an auxiliary role. Using such a system, we experimentally study a diffusion of glucose and sucrose in a gel solvent. We find a fully analytic solution of the fractional subdiffusion equation with the initial and boundary conditions representing the system under study. Confronting the experimental data with the derived formulas, we show a subdiffusive character of the sugar transport in gel solvent. We precisely determine the parameter $α$, which is smaller than 1, and the subdiffusion coefficient $D_α$.

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