Langmuir-Blodgett trough

The Langmuir-Blodgett trough is a piece of laboratory equipment used to study the properties of monolayers of amphiphilic molecules. Among other applications, the instrument can compress the monolayer to determine an isotherm, as well as deposit Langmuir-Blodgett films on a solid substrate. The instrument is named after Irving Langmuir and Katharine B. Blodgett who first introduced the concept of a monolayer.

The deposition of thin films is achieved by use of the hydrophilic or hydrophobic natures of the substance in question. For instance, to deposit a layer of lipids onto a silicon substrate, the silicon is pulled from underneath the surface of the water, through the monolayer of lipids, while the barriers are maintaining a constant surface tension. As the silicon, a hydrophilic crystal, rises through the lipids, their hydrophilic head groups attach to the silicon, transferring a monolayer to the substrate. The silicon can then be dipped back through the lipids, where the hydrophobic tails sticking out from the silicon will bond with the hydrocarbon chains sticking up from the lipids on the water. Through this process potentially many multilayers can be deposited onto a substrate. This process is limited by the strength of the bond between layers, which is typically not very strong, however, it is possible to assess the amount of molecules which have been successfully bonded to the substrate. With knowledge of the size of the substrate, the machine can calculate how many molecules have transferred to the substrate, and what percent has been covered.