Aug 2026· Journal of Contaminant Hydrology· Vol 283, pp.
105083
· 0 citations· 40 references
Medicine
Abstract
Co-contaminants can alter per- and polyfluoroalkyl substance (PFAS) mobility by modifying aqueous association, phase transfer, and retention by aquifer solids, yet how protonated amines influence these processes remains poorly constrained. Here, we investigated interactions between diisopropylamine (DIPA) and two perfluoroalkyl carboxylates with contrasting chain lengths, trifluoroacetate (TFA) and perfluorooctanoate (PFOA), using bottle tests, diffusion-ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR), retention experiments with montmorillonite, and conformer-ensemble COSMO-RS and qualitative molecular-mechanics cluster calculations. At 20-25 °C and 0.1 wt% per solute, aqueous DIPA/TFA mixtures remained optically clear, and DOSY NMR showed no convergence toward a common diffusion coefficient, consistent with weak and/or fast-exchanging association in bulk water rather than a dominant long-lived contact species. BP86/TZP COSMO-RS calculations for independently solvated ions predicted greater aqueous compatibility for DIPA+/TFA- than for DIPA+/PFOA- and a demixing tendency for the PFOA-containing conformer ensemble. In contrast, higher equimolar DIPA/PFOA loadings produced flocs or precipitates; DIPA/PFOS mixtures also precipitated. Montmorillonite retention experiments showed strong removal of DIPA, limited retention of TFA with or without DIPA, and measurable co-retention of PFOA in the presence of DIPA. These results show that favorable PFAS-amine interactions in bulk water do not necessarily translate into co-retention or reduced mobility. Instead, PFAS chain length and interfacial interactions govern whether association remains labile, as for TFA, or promotes phase transfer and mineral co-retention, as for PFOA. Thus, amine co-contaminants can differentially affect PFAS migration in clay-rich subsurface environments.
Six new phenyl-extended viologen salts with oxyethylene groups paired with triflate anions (OTF) have been synthesized using anionic ring-opening and ring-closing reactions (ANRORC) and metathesis reactions with LiOTf salts. The salts, which contain terminal oxyethylene chains of varying lengths ((CH2CH2O)n, n = 1, 2, 3, 4, 5, and 7), are named PEOn-OTF. These materials exhibit a fluorescence response and possess high thermal stability, with processing windows up to approximately 300 °C, as confirmed by thermogravimetric analysis. While samples with short chain lengths (n = 1, 2, and 3) undergo crystallization observed via differential scanning calorimetry, longer chains seem to restrict molecular packing, resulting in amorphous materials (n ≥ 4). Conductivity was studied via dielectric analysis, including an innovative approach to monitor dielectric relaxations through the imaginary component of the complex conductivity. Amorphous samples with long oxyethylene terminal chains display the highest direct current conductivity (σdc ∼ 10–3.5 S·cm–1 at 110 °C), which is of merit for organic media, but lower than that reported for trifluoromethylsulfonylimide (TFSI) analogues. Our detailed study of relaxations hints at the existence of strong correlations between morphology, dielectric response, and ion transport dynamics, which will be further explored in the near future.
Seonghyeok L. Cox, Emily Moon, Siyan Chen et al.· ACS Omega· 0 citations
The thermophysical behavior and molecular origins of dynamic viscosity (η) non-ideality in binary mixtures of acetonitrile (ACN) with six tertiary alkanolamines, namely dimethylethanolamine (DMEA), dimethylpropan-1-olamine (DMPA-1), dimethylpropan-2-olamine (DMPA-2), methyldiethanolamine (MDEA), ethyldiethanolamine (EDEA), and butyldiethanolamine (BDEA), were investigated over the full composition range at 303.15-323.15 K and 0.10 MPa. Viscosity deviations (Δη) and activation free energies of viscous flow were evaluated to elucidate intermolecular interactions. All systems exhibited predominantly negative Δη values with minima at intermediate compositions, indicating disruption of self-associated alkanolamine networks upon mixing with ACN. The magnitude of the negative deviation followed the order DMPA-2 < DMEA < DMPA-1 < BDEA < EDEA < MDEA, highlighting the influence of hydroxyl functionality, molecular architecture, and steric effects. Increasing temperature reduced the magnitude of non-ideality, consistent with weakened intermolecular interactions. Fourier-transform infrared (FTIR) spectroscopy of the representative ACN + MDEA system and density functional theory (DFT) calculations confirmed hydrogen bonding and electronic charge redistribution. Incorporation of newly optimized -CH2N interaction parameters enabled accurate viscosity prediction using the UNIFAC-VISCO (UVM) and UNIFAC-THERMO (UTM) models, yielding overall mean absolute relative deviations (MARDs) of 6.08% and 5.14%, respectively. These findings provide molecular insight into viscous-flow behavior in non-aqueous ACN-alkanolamine mixtures.
Muhammad A. R. Khan, M. Rocky, Md. Ariful Islam et al.· Physical Chemistry, Chemical...· 0 citations
β-Cyclodextrin (β-CD)-based polymers have shown high adsorption capacities for removing per- and polyfluoroalkyl substances (PFAS) from drinking water. PFAS capture by these materials involves many physical and chemical processes, such as adsorption and inclusion complexation. Quantifying the underlying host–guest binding between CDs and PFAS nevertheless remains essential because it governs the primary inclusion step. Here, we investigated native and linker-modified CD–PFAS inclusion complexes in aqueous solution using isothermal titration calorimetry (ITC) and molecular dynamics (MD) simulations with the attach–pull–release (APR) method. We computed the Gibbs free energies of binding for α-, β-, and γ-CDs with seven linear PFAS, including perfluorocarboxylic acids and perfluorosulfonic acids, and found reasonable agreement with our experimental measurements and previously reported data. Comparison between implicit and explicit solvent calculations suggests that the apparently better agreement of the implicit solvent model for some native monomer complexes is likely due to error cancellation rather than a more transferable physical description, whereas explicit solvent is required to capture solvent-related salt and linker effects. Overall, β-CD exhibited the strongest binding affinities, whereas α-CD showed negligible affinities and γ-CD bound PFAS more weakly than β-CD. Hydrogen bonding, interaction-energy decomposition, and solvent-accessible surface area showed that host–guest hydrogen bonding cannot uniquely predict affinities, and that hydrophobic dehydration plays a dominant role in binding. We further examined how background ion concentration affects β-CD–PFAS binding and found that explicit solvent simulations capture a clear salt dependence, with Li/Merz ion parameters describing the high-salinity trend more reasonably than the Joung–Cheatham model. To mimic the local microenvironment surrounding CD units in polymers, we also examined three linker-modified β-CD models containing phenyl groups. Bind3P water correctly reproduced the experimentally reported enhancement of PFAS adsorption with increasing linker number, and energy decomposition showed that linker groups strengthen PFAS binding by enhancing local hydrophobic confinement and specific linker–guest interactions. Overall, this combined experimental and computational study provides molecular-level insight into the building blocks of cyclodextrin polymers and lays the groundwork for future in silico construction of CD polymer models for PFAS adsorption under diverse water-matrix conditions.
Bowen Sha, Akhilesh Soodan, K. Lompe et al.· Journal of Physical Chemistr...· 0 citations
Extremely hydrophobic fluoromonomers are highly prone to phase separation during emulsion polymerization. Overcoming macroscopic experimental limitations, this study employs all-atom molecular dynamics (AA-MD) simulations to investigate the molecular-level solubilization behavior and thermal adaptability of the novel eco-friendly zwitterionic fluorocarbon surfactant-perfluorohexyl (butyl) sulfonyl carboxy propylamino dimethyl betaine (PFSC) and the traditional hydrocarbon surfactant SDS toward the monomers tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). Simulation results indicate that fluorinated monomers in the SDS system exhibit a more dispersed spatial distribution, with weaker local association in surfactant-enriched regions. In contrast, fluorinated monomers in the PFSC system tend to distribute within regions rich in perfluorinated segments. This spatial characteristic is consistent with thermodynamic analysis results dominated by solubility parameter matching and van der Waals interactions. Under high-temperature conditions, the perfluorohexyl sulfonyl carboxy propylamino dimethyl betaine (C6) system maintains relatively stable local spatial characteristics, with the fluorinated monomers exhibiting low migration behavior. These spatial distribution characteristics and thermal response behaviors suggest that a fluorine-rich environment may help preserve the local distribution of fluorinated monomers under high-temperature conditions. These findings provide molecular-level insights into the structure–property relationships of eco-friendly fluorinated surfactants and offer computational guidance for their rational design.
Yan-Rong Chen, Yong-Hua Shang, Kai Wang et al.· Polymers· 0 citations
Styrene-functionalized β-cyclodextrin (StyDex) polymers are structurally tunable adsorbents for removing per- and polyfluoroalkyl substances (PFASs) from water. Although specific functional elements are included in StyDex polymers to enhance PFAS adsorption, their relative contributions are not well understood. This knowledge gap hinders efforts to improve the selectivity of StyDex polymers for PFASs in complex water matrices. In this study, we characterized the adsorption mechanisms of six PFASs on three StyDex polymer derivatives. PFAS adsorption on StyDex polymers involves complementary ion-exchange (IX), host-guest complex formation, and hydrophobic interactions. The data also support the presence of synergistic non-IX mechanisms coupled to IX (IX-coupled, non-IX binding), which facilitate PFAS adsorption and are more resilient to inhibition in the presence of inorganic ions. IX and host-guest complex formation dominate at lower degrees of saturation, whereas other hydrophobic interactions become more relevant at higher degrees of saturation. PFAS adsorption inhibition is primarily attributed to IX-site competition, whereas non-IX mechanisms remain largely unaffected by inorganic ions, resulting in non-IX mechanisms becoming more important under environmentally relevant scenarios. This study establishes a general mechanistic framework for characterizing PFAS adsorption mechanisms and highlights opportunities to enhance synergistic adsorption mechanisms to improve PFAS removal performance in practical applications.
Jieyuan Wang, Zhi-Wei Lin, William R. Dichtel et al.· Environmental Science and Te...· 0 citations
Fluorine-free electrolytes are increasingly pursued for sodium-ion batteries (SIBs) to mitigate environmental and safety concerns associated with per- and polyfluoroalkyl substance (PFAS)-containing salts. However, the molecular mechanisms governing ion transport in sodium perchlorate (NaClO4)-based electrolytes remain insufficiently understood. Here, classical molecular dynamics (MD) simulations were employed to investigate how carbonate cosolvents influence solvation structure and ion association in 1 M NaClO4 electrolytes. Three solvent systems were examined: pure diglyme (G2), G2/propylene carbonate (PC), and G2/vinylene carbonate (VC). The simulations show that G2 strongly coordinates Na+ and promotes extensive ion association, dominated by multi-ion aggregates, resulting in limited ionic mobility. Incorporation of VC increases ionic conductivity (5.89 → 20.48 mS/cm, Nernst–Einstein estimate), whereas PC produces moderate enhancement. Structural analyses reveal that VC does not enter the primary Na+ solvation shell. Instead, it increases the dielectric screening of the electrolyte and weakens Na+–ClO4 – electrostatic interactions. This reduction in ion association promotes ion dissociation and facilitates faster solvent exchange dynamics, thereby improving Na+ transport. These results indicate that dielectric modulation of ion–anion interactions, rather than changes in the primary solvation structure, plays a key role in governing ion transport in NaClO4-based fluorine-free electrolytes. The findings provide molecular-level insights into the role of cosolvent dielectric properties in regulating ion association and highlight the utility of molecular simulations for understanding electrolyte behavior.
Phitchapa Ausamanwet Zijdemans, Ali Hassan, S. Kheawhom et al.· ACS Omega· 0 citations