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University of Michigan
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Reversible and irreversible Tween 80 adsorption energetics

Surfactants are surface-active amphiphilic molecules, generally containing polar and nonpolar moieties, termed head and tail, respectively. Because the head is more stable in a polar phase, and tail is more stable in a nonpolar phase, surfactant molecules are most stable at the interface between a polar and nonpolar phase. At higher concentrations, surfactants may self-assemble into aggregates called micelles, or repeating liquid crystalline microstructures such as lamellar and hexagonal phases.


We use molecuar simulation to view the microstructure and predict transient adsorption (surface tension vs. time) of surfactants. Thermodynamic data derived from simulation can predict the observed "critical surface tension" at which adsorption of Tween 80 transitions from irreversible to reversible in experiment. Because we could measure the adsorption coefficient of a surfactant which does not equilibrate at interfaces over several hours, this method gives us access to thermodynamic data that is difficult to obtain in a laboratory.


More to come...

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