eprintid: 10204901 rev_number: 7 eprint_status: archive userid: 699 dir: disk0/10/20/49/01 datestamp: 2025-02-18 11:06:27 lastmod: 2025-02-18 11:06:27 status_changed: 2025-02-18 11:06:27 type: article metadata_visibility: show sword_depositor: 699 creators_name: Kobayashi, Takeshi creators_name: Kotsi, Kristo creators_name: Dong, Teng creators_name: McRobbie, Ian creators_name: Moriarty, Alexander creators_name: Angeli, Panagiota creators_name: Striolo, Alberto title: The Solvation of Na+ Ions by Ethoxylate Moieties Enhances Adsorption of Sulfonate Surfactants at the Air-Water Interface ispublished: pub divisions: UCL divisions: B04 divisions: F43 divisions: F51 keywords: Cation-EOT complexes, Dielectric constant, Solvation, Surface tension, Surfactant mixtures note: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. abstract: Hypothesis: Experiments show pronounced synergy in the reduction of surface tension when the nonionic surfactant Poly(oxy-1,2-ethanediyl), .alpha.-tris(1-phenylethyl)phenyl-.omega.-hydroxy- (Ethoxylated tristyrylphenol, EOT) is mixed with the anionic surfactant Sodium 4-dodecylbenzenesulfonate (NaDDBS). We hypothesize that the synergism is due to counterion (cation) effects. This would be unusual as one of the surfactants is nonionic. To test this hypothesis, the molecular mechanisms responsible need to be probed using experiments and simulations. Approach: The interfacial properties of mixtures comprising EOT and NaDDBS are investigated using equilibrium molecular dynamics (MD) simulations. Free energy calculations using thermodynamic integration and umbrella sampling methods are employed to analyze the molecular interactions at surface and reveal the role of counterion solvation on the results observed. Simulation snapshots and trajectories are interrogated to confirm the findings. Findings: Simulation results indicate that the ethoxylate moieties solvate Na+ ions, forming long-lasting cation-EOT complexes. Free energy calculations suggest that these complexes are more stable at the interface than in the bulk, likely because of changes in the dielectric properties of water. The cation-EOT complexes, in turn, cause a stronger affinity between the interface and NaDDBS when EOT is present. Similar studies conducted for mixtures of EOT and cationic surfactant Dodecylammonium chloride (DAC) do not show evidence of Cl− ions solvation via the ethoxylate moieties, while the DAC headgroup was found to form hydrogen bonds with the EOT headgroup. This suggests that the mechanisms observed are likely ion specific. date: 2025-03-15 date_type: published publisher: Elsevier BV official_url: https://doi.org/10.1016/j.jcis.2024.11.229 full_text_type: other language: eng verified: verified_manual elements_id: 2340356 doi: 10.1016/j.jcis.2024.11.229 medium: Print-Electronic pii: S0021-9797(24)02817-0 lyricists_name: Angeli, Panagiota lyricists_name: Striolo, Alberto lyricists_name: Dong, Teng lyricists_name: Kotsi, Kristo lyricists_name: Moriarty, Alexander lyricists_name: Kobayashi, Takeshi lyricists_id: PANGE44 lyricists_id: ASTRI68 lyricists_id: TDONG06 lyricists_id: KKOTS36 lyricists_id: AWSMO44 lyricists_id: TKOBA44 actors_name: Kobayashi, Takeshi actors_id: TKOBA44 actors_role: owner funding_acknowledgements: EP/V032909/1 [Engineering and Physical Sciences Research Council]; [University of Oklahoma] full_text_status: restricted publication: Journal of Colloid and Interface Science volume: 682 pagerange: 924-933 event_location: United States citation: Kobayashi, Takeshi; Kotsi, Kristo; Dong, Teng; McRobbie, Ian; Moriarty, Alexander; Angeli, Panagiota; Striolo, Alberto; (2025) The Solvation of Na+ Ions by Ethoxylate Moieties Enhances Adsorption of Sulfonate Surfactants at the Air-Water Interface. Journal of Colloid and Interface Science , 682 pp. 924-933. 10.1016/j.jcis.2024.11.229 <https://doi.org/10.1016/j.jcis.2024.11.229>. document_url: https://discovery.ucl.ac.uk/id/eprint/10204901/1/manuscript_final.pdf