title: Micelle Structure and Hydrophobic Hydration.
abstract: Despite the ubiquity and utility of micelles self-assembled from aqueous surfactants, longstanding questions remain regarding their surface structure and interior hydration. Here we combine Raman spectroscopy with multivariate curve resolution (Raman-MCR) to probe the hydrophobic hydration of surfactants with various aliphatic chain lengths, and either anionic (carboxylate) or cationic (trimethylammonium) head groups, both below and above the critical micelle concentration. Our results reveal significant penetration of water into micelle interiors, well beyond the first few carbons adjacent to the headgroup. Moreover, the vibrational C-D frequency shifts of solubilized deuterated n-hexane confirm that it resides in a dry, oil-like environment (while the localization of solubilized benzene is sensitive to headgroup charge). Our findings imply that the hydrophobic core of a micelle is surrounded by a highly corrugated surface containing hydrated non-polar cavities whose depth increases with increasing surfactant chain length, thus bearing a greater resemblance to soluble proteins than previously recognized.
authors.affiliation: Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Long
authors.affiliation: Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Blake M
authors.initials: BM
authors.lastname: Rankin
authors.affiliation: Department of Chemistry, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Dor
authors.initials: D
authors.lastname: Ben-Amotz
mesh_terms: D001554:Benzene / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry; D006586:Hexanes / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D008958:Models, Molecular; D008968:Molecular Conformation; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012995:Solubility; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D006586:Hexanes; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D014867:Water; D001554:Benzene