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Haroun F, El Haitami A, Ober P, Backus EHG, Cantin S. Poly(ethylene glycol)- block-poly(propylene glycol)- block-poly(ethylene glycol) Copolymer 2D Single Network at the Air-Water Interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:9142-9152. [PMID: 32686418 DOI: 10.1021/acs.langmuir.0c01398] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In this work, Langmuir monolayers based on poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG) triblock copolymer were in situ stabilized at the air-water interface in the presence of a cross-linking agent, benzene-1,3,5-tricarboxaldehyde (BTC), in the aqueous subphase. The reaction takes place through acid-catalyzed acetalization between the terminal hydroxyl groups of the copolymer and aldehyde functions of the BTC molecules. Mean area per repeat unit measurements as a function of the reaction time show a significant monolayer contraction associated with an increase in its compressibility modulus. In addition, Brewster angle microscopy observations indicate the appearance of higher-density two-dimensional domains, irreversibly formed at constant surface pressure. This is also confirmed on a smaller scale by atomic force microscopy (AFM). These arguments, consistent with copolymer monolayer cross-linking in acidic medium, are supported in situ at the air-water interface by sum-frequency generation (SFG) spectroscopy. Furthermore, PEG-PPG-PEG monolayer cross-linking is not evidenced in alkaline medium, in coherence with the interfacial acid-catalyzed acetalization.
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Lesnicki D, Zhang Z, Bonn M, Sulpizi M, Backus EHG. Oberflächenladungen an der CaF
2
‐Wasser‐Grenzfläche erlauben eine sehr schnelle intermolekulare Übertragung von Schwingungsenergie. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202004686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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28
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Sudera P, Cyran JD, Deiseroth M, Backus EHG, Bonn M. Interfacial Vibrational Dynamics of Ice I h and Liquid Water. J Am Chem Soc 2020; 142:12005-12009. [PMID: 32573242 PMCID: PMC7467663 DOI: 10.1021/jacs.0c04526] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
![]()
Insights
into energy flow dynamics at ice surfaces are essential
for understanding chemical dynamics relevant to atmospheric and geographical
sciences. Here, employing ultrafast surface-specific spectroscopy,
we report the interfacial vibrational dynamics of ice Ih. A comparison to liquid water surfaces reveals accelerated vibrational
energy relaxation and dissipation at the ice surface for hydrogen-bonded
OH groups. In contrast, free-OH groups sticking into the vapor phase
exhibit substantially slower vibrational dynamics on ice. The acceleration
and deceleration of vibrational dynamics of these different OH groups
at the ice surface are attributed to enhanced intermolecular coupling
and reduced rotational mobility, respectively. Our results highlight
the unique properties of free-OH groups on ice, putatively linked
to the high catalytic activities of ice surfaces.
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Lesnicki D, Zhang Z, Bonn M, Sulpizi M, Backus EHG. Surface Charges at the CaF 2 /Water Interface Allow Very Fast Intermolecular Vibrational-Energy Transfer. Angew Chem Int Ed Engl 2020; 59:13116-13121. [PMID: 32239715 PMCID: PMC7496624 DOI: 10.1002/anie.202004686] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Indexed: 01/15/2023]
Abstract
We investigate the dynamics of water in contact with solid calcium fluoride, where at low pH, localized charges can develop upon fluorite dissolution. We use 2D surface‐specific vibrational spectroscopy to quantify the heterogeneity of the interfacial water (D2O) molecules and provide information about the sub‐picosecond vibrational‐energy‐relaxation dynamics at the buried solid/liquid interface. We find that strongly H‐bonded OD groups, with a vibrational frequency below 2500 cm−1, display very rapid spectral diffusion and vibrational relaxation; for weakly H‐bonded OD groups, above 2500 cm−1, the dynamics slows down substantially. Atomistic simulations based on electronic‐structure theory reveal the molecular origin of energy transport through the local H‐bond network. We conclude that strongly oriented H‐bonded water molecules in the adsorbed layer, whose orientation is pinned by the localized charge defects, can exchange vibrational energy very rapidly due to the strong collective dipole, compensating for a partially missing solvation shell.
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Deiseroth M, Bonn M, Backus EHG. Orientation independent vibrational dynamics of lipid-bound interfacial water. Phys Chem Chem Phys 2020; 22:10142-10148. [PMID: 32347258 DOI: 10.1039/d0cp01099e] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Zwitterionic phospholipids are one of the main constituents of biological membranes. The electric field associated with the two opposite headgroup charges aligns water molecules in the headgroup region. Here, we study the role of water alignment on the sub-picosecond vibrational dynamics of lipid-bound water. To this end, we compare the dynamics of oppositely oriented water associated with, respectively, a phosphocholine (PC) headgroup and an inverse-phosphocholine with non-ethylated phosphate groups (CP). We find that the dynamics are independent of the water orientation, implying that the vibrational dynamics report on the local properties of the water molecules.
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31
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Seki T, Yu CC, Yu X, Ohto T, Sun S, Meister K, Backus EHG, Bonn M, Nagata Y. Decoding the molecular water structure at complex interfaces through surface-specific spectroscopy of the water bending mode. Phys Chem Chem Phys 2020; 22:10934-10940. [PMID: 32373844 DOI: 10.1039/d0cp01269f] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The structure of interfacial water determines atmospheric chemistry, wetting properties of materials, and protein folding. The challenge of investigating the properties of specific interfacial water molecules has frequently been confronted using surface-specific sum-frequency generation (SFG) vibrational spectroscopy using the O-H stretch mode. While perfectly suited for the water-air interface, for complex interfaces, a potential complication arises from the contribution of hydroxyl or amine groups of non-water species present at the surface, such as surface hydroxyls on minerals, or O-H and N-H groups contained in proteins. Here, we present a protocol to extract the hydrogen bond strength selectively of interfacial water, through the water bending mode. The bending mode vibrational frequency distribution provides a new avenue for unveiling the hydrogen bonding structure of interfacial water at complex aqueous interfaces. We demonstrate this method for the water-CaF2 and water-protein interfaces. For the former, we show that this method can indeed single out water O-H groups from surface hydroxyls, and that with increasing pH, the hydrogen-bonded network of interfacial water strengthens. Furthermore, we unveil enhanced hydrogen bonding of water, compared to bulk water, at the interface with human serum albumin proteins, a prototypical bio-interface.
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Tang F, Ohto T, Sun S, Rouxel JR, Imoto S, Backus EHG, Mukamel S, Bonn M, Nagata Y. Molecular Structure and Modeling of Water-Air and Ice-Air Interfaces Monitored by Sum-Frequency Generation. Chem Rev 2020; 120:3633-3667. [PMID: 32141737 PMCID: PMC7181271 DOI: 10.1021/acs.chemrev.9b00512] [Citation(s) in RCA: 65] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Indexed: 12/26/2022]
Abstract
From a glass of water to glaciers in Antarctica, water-air and ice-air interfaces are abundant on Earth. Molecular-level structure and dynamics at these interfaces are key for understanding many chemical/physical/atmospheric processes including the slipperiness of ice surfaces, the surface tension of water, and evaporation/sublimation of water. Sum-frequency generation (SFG) spectroscopy is a powerful tool to probe the molecular-level structure of these interfaces because SFG can specifically probe the topmost interfacial water molecules separately from the bulk and is sensitive to molecular conformation. Nevertheless, experimental SFG has several limitations. For example, SFG cannot provide information on the depth of the interface and how the orientation of the molecules varies with distance from the surface. By combining the SFG spectroscopy with simulation techniques, one can directly compare the experimental data with the simulated SFG spectra, allowing us to unveil the molecular-level structure of water-air and ice-air interfaces. Here, we present an overview of the different simulation protocols available for SFG spectra calculations. We systematically compare the SFG spectra computed with different approaches, revealing the advantages and disadvantages of the different methods. Furthermore, we account for the findings through combined SFG experiments and simulations and provide future challenges for SFG experiments and simulations at different aqueous interfaces.
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Vaillard AS, El Haitami A, Dreier LB, Backus EHG, Cantin S. Correction to "Confinement and Cross-Linking of 1,2-Polybutadiene in 2D at the Air-Water Interface". LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:2741. [PMID: 32134678 DOI: 10.1021/acs.langmuir.0c00525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
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34
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Vaillard AS, El Haitami A, Dreier LB, Backus EHG, Cantin S. Confinement and Cross-Linking of 1,2-Polybutadiene in Two Dimensions at the Air-Water Interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:862-871. [PMID: 31935102 DOI: 10.1021/acs.langmuir.9b03297] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Langmuir monolayers of 1,2-polybutadiene (PB) were investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM) observations, and sum-frequency generation (SFG) spectroscopy. A homogeneous and stable monolayer is formed 1.5 h after PB spreading provided that both light and oxygen are present. This was attributed to a slight oxidation of the PB at the air-water interface. The cross-linking of PB under UV photoirradiation was then studied. SFG spectroscopy demonstrates the in situ formation of a two-dimensional network. From surface pressure-area characterizations and BAM experiments, the cross-linked PB monolayer appears significantly denser and more rigid than the non-irradiated monolayer. Atomic force microscopy images reveal an increase by a factor of three in the root-mean-square roughness of the irradiated monolayers compared with the non-irradiated ones.
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Das S, Imoto S, Sun S, Nagata Y, Backus EHG, Bonn M. Nature of Excess Hydrated Proton at the Water-Air Interface. J Am Chem Soc 2020; 142:945-952. [PMID: 31867949 PMCID: PMC6966913 DOI: 10.1021/jacs.9b10807] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Indexed: 01/02/2023]
Abstract
Understanding the interfacial molecular structure of acidic aqueous solutions is important in the context of, e.g., atmospheric chemistry, biophysics, and electrochemistry. The hydration of the interfacial proton is necessarily different from that in the bulk, given the lower effective density of water at the interface, but has not yet been elucidated. Here, using surface-specific vibrational spectroscopy, we probe the response of interfacial protons at the water-air interface and reveal the interfacial proton continuum. Combined with spectral calculations based on ab initio molecular dynamics simulations, the proton at the water-air interface is shown to be well-hydrated, despite the limited availability of hydration water, with both Eigen and Zundel structures coexisting at the interface. Notwithstanding the interfacial hydrated proton exhibiting bulk-like structures, a substantial interfacial stabilization by -1.3 ± 0.2 kcal/mol is observed experimentally, in good agreement with our free energy calculations. The surface propensity of the proton can be attributed to the interaction between the hydrated proton and its counterion.
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36
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Sun S, Schaefer J, Backus EHG, Bonn M. How surface-specific is 2nd-order non-linear spectroscopy? J Chem Phys 2019; 151:230901. [PMID: 31864247 DOI: 10.1063/1.5129108] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Surfaces and interfaces play important roles in many processes and reactions and are therefore intensively studied, often with the aim of obtaining molecular-level information from just the interfacial layer. Generally, only the first few molecular layers next to the interface are relevant for the surface processes. In the past decades, 2nd-order nonlinear spectroscopies including sum-frequency generation and second harmonic generation have developed into powerful tools for obtaining molecularly specific insights into the interfacial region. These approaches have contributed substantially to our understanding of a wide range of physical phenomena. However, along with their wide-ranging applications, it has been realized that the implied surface-specificity of these approaches may not always be warranted. Specifically, the bulk quadrupole contribution beyond the electric dipole-approximation for a system with a weak nonlinear interface signal, as well as the diffuse layer contribution at charged interfaces, could mask the surface information. In this perspective paper, we discuss the surface-specificity of 2nd-order nonlinear spectroscopy, especially considering these two contributions.
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37
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Seki T, Sun S, Zhong K, Yu CC, Machel K, Dreier LB, Backus EHG, Bonn M, Nagata Y. Unveiling Heterogeneity of Interfacial Water through the Water Bending Mode. J Phys Chem Lett 2019; 10:6936-6941. [PMID: 31647677 PMCID: PMC6844124 DOI: 10.1021/acs.jpclett.9b02748] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 10/24/2019] [Indexed: 05/28/2023]
Abstract
The water bending mode provides a powerful probe of the microscopic structure of bulk aqueous systems because its frequency and spectral line shape are responsive to the intermolecular interactions. Furthermore, interpreting the bending mode response is straightforward, as the intramolecular vibrational coupling is absent. Nevertheless, bending mode has not been used for probing the interfacial water structure, as it has been yet argued that the signal is dominated by bulk effects. Here, through the sum-frequency generation measurement of the water bending mode at the water/air and water/charged lipid interfaces, we demonstrate that the bending mode signal is dominated not by the bulk but by the interface. Subsequently, we disentangle the hydrogen-bonding of water at the water/air interface using the bending mode frequency distribution and find distinct interfacial hydrogen-bonded structures, which can be directly related to the interfacial organization of water. The bending mode thus provides an excellent probe of aqueous interfacial structure.
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38
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Dreier LB, Wolde-Kidan A, Bonthuis DJ, Netz RR, Backus EHG, Bonn M. Unraveling the Origin of the Apparent Charge of Zwitterionic Lipid Layers. J Phys Chem Lett 2019; 10:6355-6359. [PMID: 31568720 DOI: 10.1021/acs.jpclett.9b02587] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The structure of water molecules in contact with zwitterionic lipid molecules is of great biological relevance, because biological membranes are largely composed of such lipids. The interaction of the interfacial water molecules with the amphiphilic lipid molecules drives the formation of membranes and greatly influences various processes at the membrane surface, as the field that arises from the aligned interfacial water molecules masks the charges of the lipid headgroups from the approaching metabolites. To increase our understanding of the influence of water molecules on biological processes we study their structure at the interface using sum-frequency generation spectroscopy and molecular dynamics simulations. Interestingly, we find that water molecules at zwitterionic lipid molecules are mainly oriented by the field arising between the two oppositely charged molecular moieties within the lipid headgroups.
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39
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Das S, Bonn M, Backus EHG. Das hydratisierte Proton besitzt eine deutlich höhere Oberflächenaktivität als das Hydroxidion. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201908420] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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40
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Das S, Bonn M, Backus EHG. The Surface Activity of the Hydrated Proton Is Substantially Higher than That of the Hydroxide Ion. Angew Chem Int Ed Engl 2019; 58:15636-15639. [PMID: 31418999 PMCID: PMC6856863 DOI: 10.1002/anie.201908420] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Indexed: 11/30/2022]
Abstract
The behavior of hydroxide and hydrated protons, the auto‐ionization products of water, at surfaces is important for a wide range of applications and disciplines. However, it is unknown at which bulk concentration these ions start to become surface active at the water–air interface. Here, we report changes in the D2O–air interface in the presence of excess D+hyd/OD−hyd determined using surface‐sensitive vibrational sum‐frequency generation (SFG) spectroscopy. The onset of the perturbation of the D2O surface occurs at a bulk concentration as low as 2.7±0.2 mm D+hyd. In contrast, a concentration of several hundred mm OD−hyd is required to change the D2O surface. The hydrated proton is thus orders of magnitude more surface‐active than hydroxide at the water–air interface.
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41
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Deiseroth M, Bonn M, Backus EHG. Electrolytes Change the Interfacial Water Structure but Not the Vibrational Dynamics. J Phys Chem B 2019; 123:8610-8616. [DOI: 10.1021/acs.jpcb.9b08131] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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42
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Sun S, Tang F, Imoto S, Moberg DR, Ohto T, Paesani F, Bonn M, Backus EHG, Nagata Y. Sun et al. Reply. PHYSICAL REVIEW LETTERS 2019; 123:099602. [PMID: 31524490 DOI: 10.1103/physrevlett.123.099602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Indexed: 06/10/2023]
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43
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Nagata Y, Hama T, Backus EHG, Mezger M, Bonn D, Bonn M, Sazaki G. The Surface of Ice under Equilibrium and Nonequilibrium Conditions. Acc Chem Res 2019; 52:1006-1015. [PMID: 30925035 PMCID: PMC6727213 DOI: 10.1021/acs.accounts.8b00615] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
![]()
The ice
premelt, often called the quasi-liquid layer (QLL), is
key for the lubrication of ice, gas uptake by ice, and growth of aerosols.
Despite its apparent importance, in-depth understanding of the ice
premelt from the microscopic to the macroscopic scale has not been
gained. By reviewing data obtained using molecular dynamics (MD) simulations,
sum-frequency generation (SFG) spectroscopy, and laser confocal differential
interference contrast microscopy (LCM-DIM), we provide a unified view
of the experimentally observed variation in quasi-liquid (QL) states.
In particular, we disentangle three distinct types of QL states of
disordered layers, QL-droplet, and QL-film and discuss their nature. The topmost ice layer is energetically unstable, as the topmost
interfacial H2O molecules lose a hydrogen bonding partner,
generating a disordered layer at the ice–air interface. This
disordered layer is homogeneously distributed over the ice surface.
The nature of the disordered layer changes over a wide temperature
range from −90 °C to the bulk melting point. Combined
MD simulations and SFG measurements reveal that the topmost ice surface
starts to be disordered around −90 °C through a process
that the topmost water molecules with three hydrogen bonds convert
to a doubly hydrogen-bonded species. When the temperature is further
increased, the second layer starts to become disordered at around
−16 °C. This disordering occurs not in a gradual manner,
but in a bilayer-by-bilayer manner. When the temperature reaches
−2 °C, more complicated
structures, QL-droplet and QL-film, emerge on the top of the ice surface.
These QL-droplets and QL-films are inhomogeneously distributed, in
contrast to the disordered layer. We show that these QL-droplet and
QL-film emerge only under supersaturated/undersaturated vapor pressure
conditions, as partial and pseudopartial wetting states, respectively.
Experiments with precisely controlled pressure show that, near the
water vapor pressure at the vapor-ice equilibrium condition, no QL-droplet
and QL-film can be observed, implying that the QL-droplet and QL-film
emerge exclusively under nonequilibrium conditions, as opposed to
the disordered layers formed under equilibrium conditions. These
findings are connected with many phenomena related to the
ice surface. For example, we explain how the disordering of the topmost
ice surface governs the slipperiness of the ice surface, allowing
for ice skating. Further focus is on the gas uptake mechanism on the
ice surface. Finally, we note the unresolved questions and future
challenges regarding the ice premelt.
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Sun S, Bisson PJ, Bonn M, Shultz MJ, Backus EHG. Phase-Sensitive Sum-Frequency Generation Measurements Using a Femtosecond Nonlinear Interferometer. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2019; 123:7266-7270. [PMID: 30949276 PMCID: PMC6443213 DOI: 10.1021/acs.jpcc.9b00861] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 03/06/2019] [Indexed: 05/25/2023]
Abstract
Phase-sensitive sum-frequency spectroscopy is a unique tool to interrogate the vibrational structure of interfaces. A precise understanding of the interfacial structure often relies on accurately determining the phase of χ(2), which has recently been demonstrated using a nonlinear interferometer in conjunction with a frequency-scanning picosecond laser system. Here, we implement nonlinear interferometry using a femtosecond laser system for broadband sum-frequency generation. The phase of the vibrational response from a self-assembled monolayer of octadecanethiol on gold is determined using the nonlinear femtosecond interferometer. The results are compared to those obtained using the more traditional heterodyne-detected phase measurements. Both methods give a similar phase spectrum and phase uncertainty. We also discuss the origin of the phase uncertainties and provide guidelines for further improvement.
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Cyran JD, Backus EHG, van Zadel MJ, Bonn M. Comparative Adsorption of Acetone on Water and Ice Surfaces. Angew Chem Int Ed Engl 2019; 58:3620-3624. [PMID: 30601600 PMCID: PMC6767755 DOI: 10.1002/anie.201813517] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Indexed: 12/05/2022]
Abstract
Small organic molecules on ice and water surfaces are ubiquitous in nature and play a crucial role in many environmentally relevant processes. Herein, we combine surface‐specific vibrational spectroscopy and a controllable flow cell apparatus to investigate the molecular adsorption of acetone onto the basal plane of single‐crystalline hexagonal ice with a large surface area. By comparing the adsorption of acetone on the ice/air and the water/air interface, we observed two different types of acetone adsorption, as apparent from the different responses of both the free O−H and the hydrogen‐bonded network vibrations for ice and liquid water. Adsorption on ice occurs preferentially through interactions with the free OH group, while the interaction of acetone with the surface of liquid water appears less specific.
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46
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Das S, Bonn M, Backus EHG. The surface affinity of cations depends on both the cations and the nature of the surface. J Chem Phys 2019; 150:044706. [PMID: 30709297 DOI: 10.1063/1.5065075] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Specific ion effects at interfaces are important for a variety of thermodynamic properties of electrolyte solutions, like surface tension and the phase behavior of surfactants. We report the relative surface affinity of Na+ and D3O+ at both the D2O-air and the sodium dodecyl sulfate (surfactant)-covered D2O surface by studying the alignment of interfacial D2O, using vibrational sum frequency generation spectroscopy. The surface propensity of ions is found to be a function of both the nature of the ion and the nature of the surface. Specifically, for the charged, surfactant-covered interface, Na+ has a higher affinity than D3O+. In contrast, D3O+ has a higher affinity than Na+ at the air-D2O interface. The relative surface affinity of cations thus depends on both details of the cation and the type of interface.
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47
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Dreier LB, Bonn M, Backus EHG. Hydration and Orientation of Carbonyl Groups in Oppositely Charged Lipid Monolayers on Water. J Phys Chem B 2019; 123:1085-1089. [PMID: 30620602 PMCID: PMC6728085 DOI: 10.1021/acs.jpcb.8b12297] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The carbonyl groups of glycerolipid monolayers on water play an important role in the formation of the interfacial hydrogen bond network, which in turn influences the interactions of lipids with, for example, metabolites. As the frequency of the carbonyl absorption band strongly depends on the hydration state of the lipid headgroups, the carbonyl band is a sensitive reporter of changes in the headgroup environment. Here, we use phase-resolved sum frequency generation spectroscopy to obtain information about the orientation and hydration of the carbonyl groups in lipid monolayers. We find that there are two distinct carbonyl moieties in the lipid monolayers, oppositely oriented relative to the surface plane, that experience substantially different hydrogen-bonding environments.
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48
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Schlegel SJ, Hosseinpour S, Gebhard M, Devi A, Bonn M, Backus EHG. How water flips at charged titanium dioxide: an SFG-study on the water–TiO2 interface. Phys Chem Chem Phys 2019; 21:8956-8964. [DOI: 10.1039/c9cp01131e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photocatalytic splitting of water into hydrogen and oxygen by utilizing sunlight and a photocatalyst is a promising way of generating clean energy.
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49
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Sun S, Tang F, Imoto S, Moberg DR, Ohto T, Paesani F, Bonn M, Backus EHG, Nagata Y. Orientational Distribution of Free O-H Groups of Interfacial Water is Exponential. PHYSICAL REVIEW LETTERS 2018; 121:246101. [PMID: 30608741 DOI: 10.1103/physrevlett.121.246101] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 11/09/2018] [Indexed: 06/09/2023]
Abstract
The orientational distribution of free O-H (O-D) groups at the H_{2}O- (D_{2}O-)air interface is investigated using combined molecular dynamics (MD) simulations and sum-frequency generation (SFG) experiments. The average angle of the free O-H groups, relative to the surface normal, is found to be ∼63°, substantially larger than previous estimates of 30°-40°. This discrepancy can be traced to erroneously assumed Gaussian or stepwise orientational distributions of free O-H groups. Instead, the MD simulation and SFG measurement reveal a broad and exponentially decaying orientational distribution. The broad orientational distribution indicates the presence of the free O-H group pointing down to the bulk. We ascribe the origin of such free O-H groups to the presence of capillary waves on the water surface.
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50
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Abdelmonem A, Backus EHG, Bonn M. Ice Nucleation at the Water-Sapphire Interface: Transient Sum-Frequency Response without Evidence for Transient Ice Phase. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2018; 122:24760-24764. [PMID: 30450149 PMCID: PMC6231158 DOI: 10.1021/acs.jpcc.8b07480] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 10/09/2018] [Indexed: 06/09/2023]
Abstract
Heterogeneous ice nucleation at the water-sapphire interface is studied using sum-frequency generation spectroscopy. We follow the response of the O-H stretch mode of interfacial water during ice nucleation as a function of time and temperature. The ice and liquid states each exhibit very distinct, largely temperature-independent responses. However, at the moment of freezing, a transient response with a significantly different intensity is observed, with a lifetime between several seconds and several minutes. The presence of this transient signal has previously been attributed to a transient phase of ice. Here, we demonstrate that the transient signal can be explained without invoking a transient ice phase, as the transient signal can simply be accounted for by a linear combination of time-dependent liquid and ice responses.
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