Langmuir–Blodgett trough

A Langmuir–Blodgett trough (LB trough) is a laboratory apparatus that is used to compress monolayers of molecules on the surface of a given subphase (usually water) and measures surface phenomena due to this compression. It can also be used to deposit single or multiple monolayers on a solid substrate. A Langmuir–Blodgett trough (LB trough) is a laboratory apparatus that is used to compress monolayers of molecules on the surface of a given subphase (usually water) and measures surface phenomena due to this compression. It can also be used to deposit single or multiple monolayers on a solid substrate. The idea of a Langmuir–Blodgett (LB) film was first proven feasible in 1917 when Dr. Irving Langmuir (Langmuir, 1917) showed that single water-surface monolayers could be transferred to solid substrates. 18 years later, Dr. Katharine Blodgett made an important scientific advance when she discovered that several of these single monolayer films could be stacked on top of one another to make multilayer films (Blodgett 1935). Since then, LB films (and subsequently the troughs to make them) have been used for a wide variety of scientific experimentation, ranging from 2D crystallization of proteins to Brewster angle microscopy. The LB trough's general objective is to study the properties of monolayers of amphiphilic molecules. An amphiphilic molecule is one that contains both a hydrophobic and hydrophilic domain (e.g. soaps and detergents). The LB trough allows investigators to prepare a monolayer of amphiphilic molecules on the surface of a liquid, and then compress or expand these molecules on the surface, thereby modifying the molecular density, or area per molecule. This is accomplished by placing a subphase (usually water) in a trough, spreading a given amphiphile over the surface, and then compressing the surface with barriers (see illustration). The monolayer's effect on the surface pressure of the liquid is measured through use of a Wilhelmy plate, electronic wire probes, or other types of detectors. An LB film can then be transferred to a solid substrate by dipping the substrate through the monolayer. In addition to amphiphilic materials, Langmuir-Blodgett Troughs are commonly used nowadays to create nanoparticle coatings with controlled packing density. In early experiments, the trough was first constructed from metals such as brass. However difficulties arose with contamination of the sub-phase by metal ions. To combat this, glass troughs were used for a time, with a wax coating to prevent contamination from glass pores. This was eventually abandoned in favor of plastics that were insoluble in ordinary solvents, such as Teflon (polytetrafluoroethylene). Teflon is hydrophobic and chemically inert, making it a highly suitable material, and the most commonly used for troughs today. Occasionally metal or glass troughs coated with a thin layer of Teflon are used; however they are not as enduring as solid PTFE troughs.