Synthesis and characterization of photo- and pH-responsive nanoparticles containing amino-substituted azobenzene

Abstract

A novel dual responsive nanomaterial sensitive to both photo- and pH stimuli has been successfully developed. The polymer-based nanoparticles were fabricated from a specially designed photo- and pH-responsive amino-substituted azobenzene monomer, 4-amino-4′-methacrylatylazobenzene (AMAAB), via free radical polymerization with trimethylolpropane trimethacrylate (TRIM) cross-linkers. The trans-cis photoisomerization properties of AMAAB were retained after incorporation into the rigid three-dimensional cross-linked polymer matrix. The TRIM/AMAAB molar ratio significantly influenced the kinetics of the trans-cis photoisomerization. The nanoparticles also possessed good pH-responsive properties. The change in absorbance with media pH was monitored at 402 nm, and a “titration type” curve was obtained with a pK_a value of 0.61 ± 0.06. At this transition point, the color of the nanoparticle suspension changed colour from yellow to pink. Thermogravimetric analysis (TGA) indicated that the nanoparticles were thermally stable.