LB

The Langmuir-Bodgett (LB) device is used in the following research areas in our laboratory:

• deposition of long chain fatty acids

• surfactants and high performance long chain oil additives such as dialkyldithiophosphate acids and zinc salts (HDTP, ZDTP).

Construction and operation principle

The LB device consists of a tensiometer, Langmuir troughs, pressures sensors, motorized dipper and interface unit. All operations are computer controlled.

Generally, this deposition technique is applied for deposition of surface active compounds, e.g. surfactants trapped at the interface between two dissimilar phases - usually liquid-gas.

When surfactants or other amphiphilic compounds, dissolved in a non-aqueous volatile solvent, are introduced onto a polar liquid interface, the solvent will evaporate leaving the surfactants oriented at the liquid-gas interface: hydrophilic group pulled into the bulk water and hydrophobic group pointed into the air.

Sweeping a barrier over the water surface causes the molecules to come closer together and eventually to form a compressed, ordered monolayer. The film produced by such method is known as a Langmuir film.

When a solid substrate is immersed to the water subphase having Langmuir film on its surface, the molecules compressed at the interface attach themselves to the substrate, coating it in mono-molecular layer. Deposited on the solid substrate monolayer of molecules is called Langmuir-Blodgett film.

Being a part of the system dip-coater is frequently used as alternative method thin layers preparation for controlled deposition of sol-gel coatings on silicon substrates.

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Based on: "Tensiometers and Langmuir-Blodgett Troughs", Operating Manual, NIMA 1999