Phase Transitions in Lipid Monolayers on Water: New Light on an Old Problem
Long before exfoliated graphite, organic materials provided an easy way to make monolayers. The familiar chains formed by linking -CH2- groups are hydrophobic, while a variety of organic groups (in particular, polar groups) are hydrophilic; when combined, for example into a saturated single-chain fatty acid CH3(CH2)nCOO− H+, the resulting molecules will usually adopt one of three strategies to minimize their potential energy in an aqueous environment. They may form micelles, which are blobs with the hydrophilic head groups on the outside (in contact with water) and hydrophobic tails kept dry inside; they may form membranes, which are tail-to-tail bilayers with heads on both surfaces; or, if they are at an air-water interface, they will put their heads in the water and tails in the air. This last system is a Langmuir monolayer: you can easily make one in your kitchen sink.
KeywordsArachidic Acid Langmuir Monolayer Pentadecanoic Acid Flat Section Hydrophilic Head Group
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