Langmuir monolayer properties of 4-methylbenzenethiol capped gold nanoparticles

The properties of 4-methylbenzenethiol capped gold nanoparticles have been investigated at the air–water interface. Langmuir isotherms and compression cycles show that a stable monolayer is formed on the water surface. In situ UV-visible spectroscopy confirms that the plasmon absorption band is present which is characteristic of small metallic particles. The monolayer was imaged using real time Brewster Angle Microscopy (BAM). Above surface pressures of 5 mN m− 1 the monolayer was virtually homogeneous. During decompression, the monolayer fractured into rod-like structures. These rods were initially orientated parallel to the movable barriers containing the monolayer and as the area was increased, their orientation randomized. During subsequent compressions the rods recombined to recreate a homogeneous monolayer.