Langmuir-Blodgett Deposition of Multilayer PVDF Thin Films with NMP Solvent

Abstract

Polyvinylidene Fluoride (PVDF) is a promising homopolymer in view of its wide range of applications. PVDF thin films have been utilized in energy gathering applications, manufacturing of sensors, biological applications etc. This is due to the extraordinary behavior shown in the β-phase crystal structure of PVDF thin films exhibiting pyroelectric, ferroelectric and piezoelectric properties. The thin films of PVDF are prepared by Langmuir-Blodgett technique which provides a unique layer by layer control on the film fabrication parameters which is important from the application point of view. In the present work, the PVDF thin films are prepared by Langmuir-Blodgett deposition method with NMP solvent. To obtain good transfer characteristics the PVDF Langmuir layers were characterized for different spreading solution concentration and compression rates at 18 °C. The isotherm, hysteresis and barrier oscillation experiments show that the most stable PVDF films were obtained for spreading solution molarity of 0.0936 mol/l and 20 mm/min compression rate. These trough parameters were used for the deposition of the PVDF LB films. The role of spreading solution molarity in sharply determining the MMA and elasticity of the monolayer indicates that the initial interaction of the PVDF with the solvent (NMP) plays an important role in determining the spreading solution characteristics. A good TR is obtained for the first upstroke at 2 mm/min speed for the glass substrate. But downstrokes result in dissolution of the deposited films and also TR is reduced in the subsequent upstrokes. This indicates that Z-type nature of the PVDF LB films which is getting disrupted due to the partial dissolution of PVDF into water during downstrokes. To avoid this every single layer deposition was followed by sub-phase change. Multilayer transparent films of PVDF were synthesized by deposition of 1, 3 and 8 layers on the followed by drying and annealing. The topographic analysis of the final films shows the emergence of few large crystallites which makes the films rough.