ORIGINAL ARTICLE Enhancement of Styrene Adsolubilization and Solubilization by Rhamnolipid Biosurfactant-Linker Mixtures onto an Aluminum Oxide Surface Emma Asnachinda • Chuthanan Khampaeng • Pinpinat Sutthinon • Sutha Khaodhiar Received: 23 July 2014 / Accepted: 2 January 2015 / Published online: 17 January 2015 Ó AOCS 2015 Abstract The polarity of rhamnolipid, a relatively hydrophilic biosurfactant, can be enhanced by the addition of linker molecules. In this work, rhamnolipid biosurfac- tant-modified surfaces were prepared with and without a combination of linkers (1-butanol, 1-octanol, and 1-do- decanol) to investigate effects of linker molecules on sty- rene adsolubilization and solubilization. Results showed that styrene adsolubilization increased with increasing carbon chain lengths of the linker molecules whereas the solubilization of styrene exhibited the opposite effect. Decreasing the carbon atoms in the linker molecules resulted in higher styrene solubilization capacity because of the change in polarity of the three-dimensional surfac- tant aggregates. The higher adsolubilization capacity indi- cated the enlargement of surfactant tails that was created a larger adsolubilization region in the admicelle while the lesser solubilization of styrene indicated the decreasing of affective area per molecule of the surfactant-linker system (butanol [ octanol [ dodecanol). Keywords Rhamnolipid Á Linker molecules Á Adsolubilization Á Solubilization Á Styrene Introduction One of the problems related to groundwater and resource quality is chemicals leaking from underground storage tanks containing toxic substances and fuels [1, 2]. According to remediation technology, surfactant-modified adsorbents have recently shown a promising way to remove water pollutants such as dye, solvents, organic materials, etc. through surfactant adsorption and adsolubilization processes [3, 4]. Polymerization of a surfactant-modified surface also improves the adsorbent operating characteris- tic by decreasing surfactant loss during application. Use of less reagent for treatment also results in a cost reduction benefit [5, 6]. However, synthetic surfactants have been reported to be toxic, depending of the number of aromatic and aliphatic groups in their chemical structure, which is harmful to aquatic life and the environment [7]. To date, the naturally produced surfactants or the so-called biosur- factants have broadly generated in various forms are reported to be of low toxicity with good biocompatibility [8–11]. In addition, biosurfactants have the superior char- acteristic of lowering interfacial tensions and can be operated in extreme condition. It has been reported that they have the potential to be used in petroleum related industries for enhanced oil recovery from groundwater for both ex situ and in situ remediation including other related applications [12–14]. Adsolubilization has been acknowl- edged as a partitioning process of solute into a two- dimensionally adsorbed surfactant structure, commonly called an admicelle. Solubilization refers to the partitioning of solvent into the surfactant micelle [15–17]. Lipophilic linker molecules are amphiphiles consisting of a small head group and a long carbon chain in the tail, such as a long tail alcohol, and are thus quite hydrophobic with a low HLB (hydrophilic–lipophilic balance). Linkers enhance E. Asnachinda Chemical Engineering, Burapha University, Chonburi 20131, Thailand e-mail: emma@eng.buu.ac.th C. Khampaeng Á P. Sutthinon Á S. Khaodhiar (&) Environmental Engineering, Chulalongkorn University, Bangkok 10330, Thailand e-mail: sutha.k@eng.chula.ac.th 123 J Surfact Deterg (2015) 18:439–444 DOI 10.1007/s11743-015-1670-1