Topics in Catalysis (2022)
Riddhi Sengupta, Raghavendra, R. G. Pooja, Satyam Kumar Gupta, Bharat Kumar & Rajeev Shesha Joshi
We have studied the intervention of catalytically active nickel surface on trans–cis isomerization of azobenzene moieties, specifically in the novel polyethylene glycol itaconate-azobenzene based side chain liquid crystalline polymer (PEGIA) using Magneto Optic Kerr Effect (MOKE). We deposited thin films of nickel on glass substrate using DC magnetron sputtering and carried out MOKE studies to establish angled magnetisation in the nickel surface. A strip-like magnetic domain state was observed in these thin films studied with Magnetic Force Microscopy (MFM) which corroborates the observation of longitudinal component of magnetisation measured through Kerr rotation studies. PEGIA molecules were grafted on these Ni thin films and longitudinal MOKE was studied with and without UV exposure. We studied the effect of the trans–cis isomerization and the vice-versa on the magnetization of the nickel thin films due to the electric coupling at the magnetic surface. A substantial change of about 18.58% was observed in the magnetization during the photo-isomerization process which is attributed to change of the dipole moment of the PEGIA molecule. This change in dipole moment was corroborated with the study of variation of capacitance in the dispersive regime and the associated change in relaxation time. A 33% change in capacitance with shift in intrinsic relaxation time from 3.35 to 3.25 MHz was observed supporting the claim of change of dipole moment during the process of isomerisation. The observations collectively establish dipolar electric coupling to the magnetic surface through symmetry breaking at the interface across the cis-trans phase transition in azobenzene moieties.