Efficiently amplified ultrasonic degradation of spherical polyelectrolyte brushes by a magnetic field

Abstract

Ultrasonic degradation of polymers is well known already. This article presents an interesting and simple method about ultrasonic degradation of polymer chains which could be amplified by a magnetic field efficiently. A polystyrene-poly acrylic acid (PS-PAA) brush which averaged 238 nm in thickness was employed in the method. After ultrasonic treatment with the frequency at 35 kHz at 303 K for 6 hours, the thickness of PAA chains decreased by 83 nm while it decreased by 180 nm dramatically with the same ultrasonic irradiation coupled with a magnetic field (20 mT). It implied that there was a synergetic effect of ultrasound and magnetic field on the degradation of PAA chains. Increasing the magnetic field intensity or ultrasonic frequency could decrease the residual thickness of PAA chains as well as which could be done by decreasing the temperature. In the experimental range, it's surprising that the thickness of PAA chains decreased from 238 nm to 14 nm after 5 h treatment (20 mT, 53 kHz, 288 K) and the average molecular weight of the PAA chains on the surface of the core decreased from 2.5 × 10⁵ to 1.5 × 10⁴ g mol⁻¹. Different characterizations, such as UV-vis, FTIR, DLS, rheology, KI dosimetry and calorimetry study etc. were employed in this work. Based on the experimental results, a reasonable mechanism was proposed as the magnetic field decreased the viscosity of the brush solution which could enhance the effect of the acoustic cavitation. In all, this work provides a simple and green method on the degradation of polymer brushes and may have applications in material chemistry and environmental engineering in future.