Diffusion of Probe Polyelectrolyte in the Acrylamide-co-Sodium Acrylate Polyelectrolyte Gel

Abstract

Introduction Hydrogels are 3D polymeric networks that can swell in the aqueous medium. Because of their water-absorbing capacity, non-toxicity, and biocompatibility, they have applications in bioengineering, drug delivery and separation processes. The gel matrix has the property to govern the diffusion of foreign particles within its network. So, it is vital to understand the parameters that affect solute diffusion as they have applications in many fields. In the present study, acrylamide-co-sodium acrylate (AAm/SA) hydrogel is taken as the polyelectrolyte gel with 10% charge density, and the diffusion of probe sodium polystyrene sulfonate polyelectrolyte (NaPSS) is studied with the help of the dynamic light scattering (DLS) method. Method Using free radical polymerization, AAm/SA hydrogel is prepared. The total monomer concentration was fixed at 5 wt% and mixed with a cross-linker of -methylenebisacrylamide. This pre-gel mixture was added to the initiator, potassium persulfate and activator, TEMED and kept overnight for gelation. The DLS measurements were taken on a home-built setup consisting of a LASER as an excitation source, a fibre-coupled avalanche photodiode as a detector and an ALV correlator. The sample being non-ergodic in nature, direct ensemble-averaged intensity-intensity correlation function, g2 (q,t) was obtained on a rotating sample using the ALV correlator. Results Changes in gel dynamics are studied with varied incorporated NaPSS concentrations. The dynamic information of the hydrogels is extracted from the field correlation function g1 (q,t) related to g2 (q,t) by Siegert relation, g2 (q,t) = 1+b 1 2, where b is the instrumental constant. The obtained g1 (q,t) were fitted with a single plus stretched exponential equation,g1 (q,t) = af*exp(-t/ f) +as*exp(-t/ s) +g1 (q, ) s f It is seen that the fast relaxation time increases with the rise in NaPSS concentration. Hence, the diffusion rate of the gel network gradually decreases. This means the embedded polyelectrolyte chains increase the correlation length of the gel matrix by loosening the gel network. Also, the slow relaxation time increases when the external polymer concentration increases.