Neutral polymer-pseudo polyelectrolyte transition of a post irradiated polymer dissolved in water

Abstract

The purpose of this study is to study the conformation transition of a post irradiated polymer dissolved in water. In fact, polyvinylpyrrolidone (PVP) in powder(Mw = 1.300.000 g/mol), is irradiated with various doses, D, ranged from 0.3 to 50 kGy of 60Co-gamma. The irradiated polymer, PVP*, is dissolved in water to obtain post irradiated solutions of different concentration. After the stabilization of the obtained solutions (48 h), refractometry and viscosity measurements, are used to characterize the post irradiated aqueous solutions at 25 °C. The specific volume of PVP* dissolved in water was determined according modified Lorentz-Lorenz and Gaston-Dale equations, showing two dependence on the dose, D. For D ≤ Dc = 20 kGy, the specific volume increases and for D ≥ Dc, the specific volume decreases. The reduced viscosity of PVP*(Mw = 1.300.000 g/mol) aqueous solution permits to delimit the dilute and semi dilute regimes concentration and deduce the overlapping concentration, C*PVP*(D), which found to be insensitive to the dose value. For D < Dc, the intrinsic viscosity PVP* dissolved in water is determined according a modified Huggins equation and so the irradiated polymer behaves as neutral polymer. However, when D = DC the intrinsic viscosity values calculated according modified Fuoss and Fedors equations are very close and the irradiated polymer behaves as a polyelectrolyte in water. For D > Dc, the modified Fedors equation describes perfectly the evolution of the reduced viscosity versus irradiated polymer concentration. So, PVP* behaves as a polyelectrolyte in water and a neutral polymer – pseudo polyelectrolyte transition occurs under gamma irradiation effect. The irradiated polymer molar mass, MwPVP∗(D), was determined by comparing its intrinsic viscosity to these established according the Mark Howink Shakurada equation. MwPVP∗(D) decreases by increasing the dose value, which confirm the scission the polymer chain under gamma irradiation effect.