Polyacrylamide (PAAm) hydrogels are obtained by free-radical crosslinking copolymerization of acrylamide (AAm) and N,N'-methylene-bis-acrylamide (Bis) monomers, in bidistilled water, initiated by potassium peroxodisulfate (KPS) and accelerated by ascorbic acid (AAs), system which have a rate independent of the oxygen presence. This system of initiation has an autocatalytic reaction according to the following process:

Reduction of peroxydisulphate by ascorbic acid follows a chain mechanism in which ascorbic acid is oxidized to dehydroascorbic acid

Ascorbate radicals (AH-.) and sulphate ion radicals (SO4-. ) are the active species which initiate the polymerization

The presence of molecular oxygen in the reaction system, instead of inhibiting, autocatalysis the polymerization rate.

The poly(acrylamide) gel was prepared by redox solution copolymerization of AAm and Bis at a concentration of monomers of 6 wt % in bidistilled water, in glass ampoules with 12 mm diameter and 130 mm length, at room temperature (20 - 25 ° C) for 24 hrs, for complete gelation. A typical procedure can be described as follows: AAm and Bis were dissolved in distilled water to form stock solutions. KPS and AAs solutions were added to the monomers solution mixture, respectively. The reaction components were purged into the glass ampoule and the polymerization was performed:

The obtained gels have a cohesive network structure:

There were experimented different synthesis conditions in relation with the subsequent application:

Synthesis in the presence of a magnetic field of 1100 Gs, with the aim of underlining the effect of the field and of the crosslinker content on the structure and swelling behaviour of the poly(acrylamide) hydrogel (in Proceedings at the International Conference on Materials Science and Engineering, BRAMAT, BRASOV , 22 – 26 februarie 2005, more…).

Synthesis of poly(acrylamide) hydrogels with varying amount of crosslinker Bis in AAm / Bis feeding molar ratio for comparing the dynamic swelling behavior and surface morphology (in Revista Medico-Chirurgicala, vol. 110, nr. 1, more…).

In situ real time, pH and conductivity experiments as a kinetic image for gelation of poly(acrylamide), by classical procedure and in the presence of a magnetic field of 2500Gs (Proceedings at the VIII th Symposium on colloids chemistry and surfaces, 2005, more…).

The rheological behavior during in situ gelation process of acrylamide crosslinked with N, N' - methylenebisacrylamide using the redox system of initiation potassium persulfate / ascorbic acid and also the monitoring of the synthesized gels as thermoresponsive products, was also studied ( Proceedings at the VIII th Symposium on colloids chemistry and surfaces, 2005, more…).

Monitoring of the gelation process in real time during the crosslinking copolymerization of AAm with Bis, by dynamic and static procedures. In situ polymerization processes were carried out at different onset initiator / accelerator ratios for a given Bis content (in Journal of Optoelectronics and Advanced Materials, Volume 8, No. 1, 2006, more…).

The effects of heating rate and shear stress on the sol-gel transition for a polyacrylamide gel during in situ preparation were investigated by dynamic rheology. The gelation evolution was also studied through monitoring of the static gelation process by means of temperature, pH and conductivity variation. The gels were prepared by polymerization of acrylamide crosslinked with N, N' - methylenebisacrylamide using a redox initiation based on potassium persulfate / ascorbic acid. In situ gelation process was studied using oscillatory deformation tests at constant frequency of 0.1 Hz for different heating rate (from 0.5 ° C/min to 5° C/min) and shear stress (in the range of 0.1Pa to 10Pa). The rheological data are in agreement with the evaluation through in real time monitoring of the static gelation process (presented at the 3rd Annual European Rheology Conference www.rheology-esr.org/AERC/2006 , April 26-30, Hersonisos – Crete , more…).

Investigation of the induced differences of swelling and thermal behaviour dependence on the amount of crosslinking comonomer ( in Journal of Optoelectronics and Advanced Materials, Volume 8, No. 3, 2006 more…).

Monitoring in situ gelation process of poly(acrylamide) with Bis by dynamic oscillatory testing from the viewpoint of elastic and viscous response characterized by storage (G') and loss (G'') moduli, gelation time, for different initiator / activator molar ratios (presented at the 3rd Annual European Rheology Conference www.rheology-esr.org/AERC/2006 , April 26-30, Hersonisos – Crete, more…).