Absorption properties and structure changes caused by pre-annealing in polydiacetylene Langmuir-Blodgett films

Abstract

Absorption properties and structures are investigated as a function of pre-annealing temperature for PDA LB films. Absorption spectra of PDA LB films without pre-annealing have main peaks at 640 nm, while the pre-annealed 10-8 PDA LB films have new absorption peaks at 704 nm, i.e. a new blue phase. X-Ray diffraction measurements show that the pre-annealed films have extremely ordered layer structures. However, main peaks are observed at 640 nm for the pre-annealed 14-8 PDA LB films and the peaks only decrease with pre-annealing, because the layer spacing increases with pre-annealing and the polymerization is disturbed. Properties to the 10-8 PDA LB films depend upon the deposition temperature. The films, deposited at 20 °C and at 13 °C, have similar properties to the 10-8 PDA LB films and the 14-8 PDA LB films, respectively. The films having 704 nm peaks exhibit strong reversible color phase transitions between the new blue phase and the red phase. Pre-annealing is thought to be an important technique for controlling and improving characteristics of LB films.