title: Aggregate-based sub-CMC Solubilization ofn-Alkanes by Monorhamnolipid Biosurfactant.
abstract: Solubilization ofn-decane, dodecane, tetradecane and hexadecane by monorhamnolipid biosurfactant (monoRL) at concentrations near the critical micelle concentration (CMC) was investigated. The apparent solubility of all the four alkanes increases linearly with increasing monoRL concentration either below or above CMC. The capacity of solubilization presented by the molar solubilization ratio (MSR), however, is stronger at monoRL concentrations below CMC than above CMC. The MSR decreases following the order dodecane > decane > tetradecane > hexadecane at monoRL concentration below CMC. Formation of aggregates at sub-CMC monoRL concentrations was demonstrated by dynamic light scattering (DLS) and cryo-transmission electron microscopy examination. DLS-based size (d) and zeta potential of the aggregates decrease with increasing monoRL concentration. The surface excess (Γ) of monoRL calculated based on alkane solubility and aggregate size data increases rapidly with increasing bulk monoRL concentration, and then asymptotically approaches the maximum surface excess (Γmax). Relation betweenΓanddindicates that the excess of monoRL molecules at the aggregate surface greatly impacts the surface curvature. The results demonstrate formation of aggregates for alkane solubilization at monoRL concentrations below CMC, indicating the potential of employing low-concentration rhamnolipid for enhanced solubilization of hydrophobic organic compounds.
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, USA.
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: Xin
authors.initials: X
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: Fei
authors.initials: F
authors.lastname: Tan
authors.affiliation: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brusseau
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: 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: Guangming
authors.initials: G
authors.lastname: Zeng
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
keywords: aggregation; biosurfactant; critical micelle concentration; monorhamnolipid; n-alkane; solubilization