Experimental investigations using mass spectrometry have established that surfactant molecules are ableto form aggregates in the gas phase. However, there is no general consensus on the organization ofthese aggregates and how it depends on the aggregation number and surfactant molecular structure. Inthe present paper we investigate the structural organization of some surfactants in vacuo by moleculardynamics and well-tempered metadynamics simulations to widely explore the space of their possibleconformations in vacuo. To study how the specific molecular features of such compounds affect theirorganization, we have considered as paradigmatic surfactants, the anionic single-chain sodium dodecylsulfate (SDS), the anionic double-chain sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and thezwitterionic single-chain dodecyl phosphatidyl choline (DPC) within a wide aggregation number range(from 5 to 100). We observe that for low aggregation numbers the aggregates show in vacuo the typicalstructure of reverse micelles, while for large aggregation numbers a variety of globular aggregates occurthat are characterized by the coexistence of interlaced domains formed by the polar or ionic heads andby the alkyl chains of the surfactants. Well-tempered metadynamics simulations allows us to confirmthat the structural organizations obtained after 50 ns of molecular dynamics simulations are practicallythe equilibrium ones. Similarities and differences of surfactant aggregates in vacuo and in apolar mediaare also discussed.
|Number of pages||7|
|Journal||Physical Chemistry Chemical Physics|
|Publication status||Published - 2015|
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy
- Physical and Theoretical Chemistry