Brewster Angle Microscopy provides a perfect solution for non-invasive imaging of Langmuir monolayers at the air-water interface. Real-time observation and recording of film structure enables dynamic activity to be captured, without the need of any microscopy agents that could interfere with the Langmuir layer.

A MicroBAM enables the visualization of Langmuir monolayers or adsorbate films at the air-water interface. BAM utilizes the reflection-free condition that occurs when p-polarized light is guided towards an air-water interface at a specific incident angle. This angle is called the Brewster angle, and is determined by Snell’s law and depends on the refractive indices of the materials in the system.

Snell’s law

 tan α = n2 / n1

  • α — Brewster angle in radians
  • n1 — Refractive index of air (≈1)
  • n2 — Refractive index of water (≈1.33)

The Brewster angle for the air-water interface is 53°, and under this condition the image of a pure water surface appears black. Addition of material to the air-water interface modifies the local refractive index (RI) and this causes a small amount of light to be reflected and displayed within the image. The image displayed contains areas of varying brightness determined by the particular molecules and packing densities across the sampling area.

KN_BAMoverTrough.jpg

Measurement examples

KSV-NIMA-MicroBAM-stearic-acid-monolayer-formation.jpgStearic acid monolayer formation during compression (KSV NIMA MicroBAM)

For more information, see: 

Application Note 9 — Imaging the Structure of Thin Films: Brewster Angle Microscopy

KSV NIMA offers the Micro Brewster Angle Microscopy model. It can be combined with KSV NIMA L&LB Troughs.