Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2‐ethylhexyl)sulfosuccinate |
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Authors: | Giovanna Longhi Alberto Ceselli Sandro L Fornili Sergio Abbate Leopoldo Ceraulo Vincenzo Turco Liveri |
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Institution: | 1. Dipartimento di Scienze Biomediche e Biotecnologie, Università di Brescia, , 25123 Brescia, Italy;2. CNISM, Consorzio Interuniversitario Scienze Fisiche della Materia, , 00146 Roma, Italy;3. Polo Didattico e di Ricerca di Crema, Universita' di Milano, , 26013 Crema, CR, Italy;4. Dipartimento STEBICEF, Università di Palermo, , 90123 Palermo, Italy;5. Centro Grandi Apparecchiature, UniNetLAb, , 90128 Palermo, Italy |
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Abstract: | The behavior of aqueous solutions of sodium bis(2‐ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N0AOT AOT? anions (N0AOT = 0, 5, 10) and N0Na sodium ions (N0Na = 0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N0AOT and N0Na eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions. Copyright © 2013 John Wiley & Sons, Ltd. |
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Keywords: | AOTNa electrospray ionization aqueous nanodroplets charged reverse micelle‐like aggregates molecular dynamics simulation |
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