title: Aggregate-based sub-CMC Solubilization of Hexadecane by Surfactants.
abstract: Solubilization of hexadecane by two surfactants, SDBS and Triton X-100, at concentrations near the critical micelle concentration (CMC) and the related aggregation behavior was investigated in this study. Solubilization was observed at surfactant concentrations lower than CMC, and the apparent solubility of hexadecane increased linearly with surfactant concentration for both surfactants. The capacity of SDBS to solubilize hexadecane is stronger at concentrations below CMC than above CMC. In contrast, Triton X-100 shows no difference. The results of dynamic light scattering (DLS) and cryogenic TEM analysis show aggregate formation at surfactant concentrations lower than CMC. DLS-based size of the aggregates (d) decreases with increasing surfactant concentration. Zeta potential of the SDBS aggregates decreases with increasing SDBS concentration, whereas it increases for Triton X-100. The surface excess (Γ) of SDBS calculated based on hexadecane solubility and aggregate size data increases rapidly with increasing bulk concentration, and then asymptotically approaches the maximum surface excess (Γmax). Conversely, there is only a minor increase in Γ for Triton X-100. Comparison of Γ anddindicates that excess of surfactant molecules at aggregate surface has great impact on surface curvature. The results of this study demonstrate formation of aggregates at surfactant concentrations below CMC for hexadecane solubilization, and indicate the potential of employing low-concentration strategy for surfactant application such as remediation of HOC contaminated sites.
authors.affiliation: College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha, 410082, China; Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona 85721, U.S.A.
authors.forename: Hua
authors.initials: H
authors.lastname: Zhong
authors.affiliation: College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha, 410082, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.affiliation: College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha, 410082, China.
authors.forename: Guangming
authors.initials: G
authors.lastname: Zeng
authors.affiliation: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona 85721, U.S.A.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brusseau
authors.affiliation: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona 85721, U.S.A.
authors.forename: Yake
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha, 410082, China.
authors.forename: Zhifeng
authors.initials: Z
authors.lastname: Liu
authors.affiliation: College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha, 410082, China.
authors.forename: Xingzhong
authors.initials: X
authors.lastname: Yuan
authors.affiliation: College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha, 410082, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Tan
keywords: SDBS; Triton X-100; aggregation; critical micelle concentration; solubilization; surfactant