Abstract
Langmuir-Blodgett (LB) film deposition technique has received wide attention owing to its potential applications for monolayer or ultra-thin film production. Until now, LB technique remains only a laboratory tool with very limited industrial applications due to its slow deposition speed and lack of reliability. The aim of the present study is to experimentally investigate the stable and higher deposition speed for LB film deposition. There are some factors to affect the LB film deposition which include arrangement of interface molecules, dynamic contact angles, fluid motion and characteristic of substrate and sub-phase. Therefore, in this paper has developed a systematic methodology involving several experimental steps and measurements before, during and after the LB film deposition process, to ensure the production of the LB film deposition. First, we are concerned with the LB film deposition of arachidic acid, particularly the maximum withdrawal speed with acceptable transfer ratio. A Langmuir minitrough that provides the surface pressure vs molecular area (□-A) curve and a flow visualization technique were served as tools to investigate the maximum withdrawal speed with negligible water entrainment. The effect of hydrophobic and hydrophilic substrates and the addition of four different ions, eg, K+,Ba2+,Cd2+ and Al3+, on the withdrawal speed were examined. It was found that the “transition point” from liquid state to solid state on the □-A curve can serve as a clear indicator on the maximum withdrawal speed, i.e., the lower the transition point, the higher the maximum withdrawal speed. Owing to the “soap effect” of the divalent ions Ba2+ or Cd2+, stable fluid motion for successful LB film deposition can be increased to 60mm/min. The quality of LB deposited film was examined with atomic force microscopy (AFM). An experimental study was also carried out to examine the stable LB film deposition of mixtures of Polyaniline (PA) and Arachidic acid (AA) at different concentration ratios. Images of the PA/AA composite materials at air-liquid interface, based on the Brewster angle microscopy, revealed that a 50/50 concentration ratio of PA/AA composite layer produced the best LB film structure. The feasibility of LB film deposition was determined from dynamic contact angles which were measured by a flow visualization technique. The quality of the deposited film was also judged by the transfer ratio and the atomic force microscopy (AFM) images. The effect of pH was also examined, and it was found that the LB film deposition for the PA/AA system could only be carried out in a narrow range of pH. It was found that the deposited LB film of the PA/AA system had a high transfer ratio and improved surface roughness at the deposition speed 30mm/min.