Heat of adsorption of surfactants and its role on nanoparticle stabilization |
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| Institution: | 1. Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. bl. 9, 1113 Sofia, Bulgaria;2. Institute of Organic Chemical Technology, West Pomeranian University of Technology Szczecin, Pulaski Str. 10, 70-322 Szczecin, Poland;3. Department of Inorganic and Analytical Chemistry, West Pomeranian University of Technology Szczecin, Piastow 42, 71-065, Szczecin, Poland;4. Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 21, 1113 Sofia, Bulgaria;1. Institute of Physics, University of Sao Paulo, Brazil;2. Institute of Fluid Mechanics, Technische Universität Dresden, Germany;1. Université de Lille 2, Droit et Santé, 42 rue P. Duez, 59000 Lille, France;2. CNRS-ICMPE, 2 rue H. Dunant, 94320 Thiais, France;1. Ecole Polytechnique Federale de Lausanne, Institut des Materiaux, Laboratoire des Polymeres, Batiment MXD, CH-1015 Lausanne, Switzerland;2. Centre of Advanced Research in Bionanoconjugates and Biopolymers, “Petru Poni” Institute of Macromolecular Chemistry of Romanian Academy, 41A Grigore Ghica Voda Alley, 700487 Iasi, Romania;3. Department of Textiles and Leather Chemical Engineering, “Gheorghe Asachi” Technical University of Iasi, 700050 Iasi, Romania;4. Nicolina Medical Center, CMI Dermatology, 2 Hatman Sendrea Street, 70063 Iasi, Romania |
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| Abstract: | In this work, the binding between sodium oleate (SO), sodium laurate (SL), sodium dodecyl sulfate (SDS), and sodium dodecylphosphonate (SDP) and iron oxide nanoparticles was systematically investigated using isothermal titration calorimetry (ITC). Comparing the heat exchanged during the isothermal titration with the corresponding surfactant adsorption isotherm, in the cases of SO and SDP, a strong binding takes place at low surfactant concentrations. The binding enthalpy at this low surfactant concentrations depends on the type of surfactant anionic head group. For C12 surfactants, the phosphonate group produced the strongest endothermic binding, followed by the exothermic binding with the carboxylate group, followed by weak exothermic interaction with the sulfate group. For carboxylate surfactants, longer surfactant tails result in larger exothermic binding. Surfactants that exhibited large binding enthalpies also produced more stable suspensions. The Langmuir (L), Freundlich (F), and Langmuir–Freundlich (L–F) adsorption models were used to interpret the adsorption isotherms during the titration with sodium oleate. The L–F adsorption isotherm model was selected to calculate the heat of the formation of the SO monolayer and bilayer on the iron oxide nanoparticles. The L–F model reflects the finite or limited adsorption of the Langmuir model, but accounts for non-homogeneous adsorption of the Freundlich model that help account for surfactant self-assembly before and after adsorption. Coupling the adsorption model with the titration data is possible to calculate the real heat of adsorption of the surfactants on the metal oxide. |
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| Keywords: | Adsorption Surfactant Stabilization Nanoparticle Titration Calorimetry |
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